**FTS-NASA-VOICE**

**Moderator: Trina Ray**

**February 28, 2006**

**1:00 pm CT**

Coordinator: Excuse me, this is the conference coordinator. At this
time, I would like to inform all participants that today's call is being
recorded. If anyone has any objections, you may disconnect at this time.

Thank you.

You may begin.

Man: Okay. Thank you.

Trina Ray: Well welcome everyone to the CHARM telecon for February of
2006. We have a terrific talk today.

Dr. Ralph Lorenz, who's a Surface Science Package co‑investigator for
the Huygens probe, is going to be talking about not only the
penetrometer and the Surface Science Package but also all of the
interesting science results from the Huygens probe one year later.

To remind everyone there is a Web site with PowerPoint that is password
protected so folks can download that if they have access to it and the
PDF is available on our normal CHARM Web site available to the public.

And with that, I'll turn it over to Dr. Lorenz.

Ralph Lorenz: Okay, thank you.

Well the task I was given today was to sort of summarize, you know,
where Huygens is. Obviously it made a lot of news a little over a year
ago and in the meantime, the teams have been busy interpreting the data
and publishing the findings. And so it seems one year later, an
opportune moment to kind of recap.

Of course Cassini data is coming in all the time and it's changing our
perceptions of Titan, but a lot of those perceptions are really anchored
in what the Huygens probe told us.

So I'm not really going to address some of the exciting stuff, the
orbiter's been doing.

We have some pretty exciting new things with the radar that will be
talked about at the Lunar and Planetary Science Conference in a couple
of weeks and some of that material is going to be published in Science;
so it's presently under embargo so that's one other reason I'm not going
to be talking about it today.

For me personally, this project, the Huygens project isn't so much the
highlight of my career, as it's been my entire career. I trained as an
aerospace engineer in the UK and 1990 got my first job as what's called
a young graduate trainee at the European Space Technology and Research
Centre, ESTEC in the Netherlands. And I was lucky enough to be assigned
to the Huygens project just when it began, just at the start of Phase B
when the designs were being refined and the payloads have just been
chosen.

So it was a wonderful first job, a wonderful introduction to the world
of work and the space industry and it gave me a chance to - really to
see the Cassini project from the top down a little bit (unintelligible)
sort of one year fixed appointment. And I then went on to the University
of Kent in Canterbury in the UK where I worked with John Zarnecki, the
PI of the Surface Science Package on building part of the Surface
Science Package, which I'll talk about a bit later.

And then since '94, I've been here at the University of Arizona working
on Titan in a number of capacities \-- working with Hubble space
telescope images, we made the first maps of Titan back in '95-'96, and
science planning for the Cassini radar, and the ongoing activities with
the probe preparing for our big day last year.

The picture here is me in Darmstadt last year during a probe encounter.
The probe you see there is a model called SM2, Special Model 2, that was
used for parachute drop tests in - when was it, 1994 maybe '96. So this
thing was taken up to 40 kilometers altitude on a big helium balloon in
northern Sweden and dropped to show that the three different parachutes
all deployed correctly in sequence and the front shield fell away.

The sort of blue and metallic bits at my crotch are the attach
mechanisms for the front shield. You can see around the bottom of the
probe a set of little wings, little spin vanes. These look like they're
oriented vertically but they're actually canted by about 3 degrees to
impart a steady spin to the probe to pan the camera around, and we'll be
talking a bit more about spin.

There are a couple of cylindrical cavities on the top surface there.
Those are the parachute mortar, the container for the pilot chute. The
big square box is the container for the main parachute.

You may see some artist's impressions. There was one that came out just
a few weeks ago that, you know, it's supposed to be the probe sitting on
the surface of Titan and you can see that box is actually closed so as
if the parachute never came out. So that's one little (gotcha) to watch
out for.

But that's the full size of the Huygens probe. It's 1.3 meters in
diameter and the real thing weighed about 200 kilograms.

We go on to the next slide, make a shameless plug for a book that's now
maybe more of historical interest inasmuch as Lifting Titan's Veil, kind
of summed up what we thought we knew about Titan and why we thought we
knew it before Cassini arrived and describes some of the activities
during the Huygens and Cassini development.

There's a bit of a discussion in my other book, Space System Failures,
on the receiver anomaly.

Huygens data was transmitted by the probe on two channels and received
by receiver on the orbiter and was also supplied by ESA. And during the
Earth flyby, there was a design flaw was uncovered during a test where
one of the DSN antennas was used to sort of pretend to be the Huygens
probe just to test the data link from one end to the other.

End‑to‑end testing is always time-consuming and difficult and expensive
to do and but it's always worth doing if you can. And this test, you
know, uncovered a flaw that would have crippled the mission had it not
been discovered and a workaround developed.

Basically we had to change some of the software on the receiver. We
switched the Huygens probe on four hours early so that it would warm up.
There's a little bit of a temperature dependence of the quartz
oscillators in the receiver and on the probe transmitters. And by
warming the probe up by a few degrees extra, the clocks drifted a little
bit to improve the synchronization. And the main change of course was to
change the orbiter's trajectory to change the Doppler effect.

And so after all that exercise, which thankfully we had plenty of time
to do, I mean if we're going to the moon or Mars we just wouldn't have
had time to engineer a solution like that, but since we had another five
years to go to Saturn, we had time to develop this workaround. And that
workaround seems to have worked very well.

So that's in there.

Of course there's a lot more we know about Titan now than we did before
so I'm busy working on a sequel to Lifting Titan's Veil called Titan
Unveiled.

Okay, so just to sum up the probe mission on the third slide here, it
was the 14th of January, a day that will be etched in the history books,
I guess. The first results kind of came out within hours \-- I mean, the
event was really quite a media circus. I mean this was really last new
world that we'll see up close. You can argue perhaps that, you know, we
haven't seen Pluto up close and we haven't, you know, been to Triton,
but at some level these bodies will all look the same and look like we
thought they should be having seen them from Voyager or from ground base
telescopes.

Titan was really hidden and because it has an atmosphere and perhaps
methane hydrological cycle maybe it was going to look a lot like Earth
but we really didn't know. Maybe it would be just a cratered world like
Callisto that just happened to have an atmosphere.

So it was really quite an event. There was maybe about 80 scientists at
ESA which is not a particularly big facility. There are only maybe 800,
I think, people work there generally. But there are 80 scientists and
maybe 200 media \-- I mean, the place was besieged by, you know, camera
crews and journalists. It was really quite a high pressure kind of
thing, not something I'd want to do every year.

It took a while to get the findings documented in a more formal fashion;
the first results papers came out in December in a special issue of
Nature. For some reason we didn't quite make it to the front cover and
so there's a picture of a dog on it because in the same issue they
published the dog genome. I guess the editors have no sense of taste,
but there we go.

Now there's a lot more sort of more detailed kind of follow-up work
going on. There's a special issue of Journal of Geophysical Research
going to come out with the ground base observations that were going on
during the probe mission.

You may remember Jupiter was explored by a probe, the Galileo probe, and
its results really are rather puzzling in that there was a lot less
oxygen or rather a lot less (unintelligible). And that was really a
puzzle but was understood because there were ground base observations
going on at the time and what happened was - with Galileo was the probe
entered what's called a 5-micron hotspot, a region of down-welling dry
air where the clouds are basically cleared by the down-welling air and
that left the warm glow of Jupiter's deep interior kind of shine
through.

So it was kind of lesson that you \-- one, you should never have single
probe if you can afford more in that you have this sampling problem it
may be picking a unique spot and not really sampling a diversity of the
place and that may be really true somewhere as diverse as Titan or, you
know, ideally mobility is another solution. But if you have a single
probe then you better make sure you have other observations to provide
context to understand what the in-situ ground truth the probe is telling
you correspond to \-- is it the sort of average view of the planet or is
it somewhere special.

So there were a lot of telescopes pointed at Titan during the probe
mission. Those are getting published.

And as, you know, after individual teams, you know, sit down and publish
their own results, there's a lot more correlative analysis going on. Now
teams are talking to each other and comparing notes, you know, did you
see something go on at, you know, 2000 seconds or whatever.

And then we start running into just the sort of forensic engineering of,
you know, what exactly happened and how simultaneous are things and it
turns out that, you know, the time stamps on some dates were offset with
respect to another. But, you know, just a third of second, I mean, it's
not a big deal. But you do need to understand that sort of thing because
if it's not worked out and documented now it never will be.

The probe data which includes some of the engineering data are going to
be publicly available in July on the ESA Planetary Science archive and
that will be echoed on the NASA Planetary Data System. So everyone can
get hold of all the data and misinterpret it as much as they want. But
the important thing is to get stuff documented so that the context for
all that material is laid out.

There'll be comparisons with Huygens data with observations from the
orbiter throughout the orbiter mission; so the Huygens scientists are
continuing to be involved. In particular, in October, there was an
observation at the landing site by the radar instruments, and we'll talk
about that a little bit more, and that really nailed down the location
of the probe landing site. We were pretty sure we knew where it was
roughly but comparison with the radar really nailed it.

Now there's another technique used to determine where the probe was in
the sky, a Very Long Baseline Interferometery where you chain a load of
radio telescopes together and effectively synthesize a radio telescope
that's, you know, more or less the size of the Earth and that will give
an independent measure of the approach trajectory in fact in a different
dimension from the other measures. And we expect that to match up with
what we think (unintelligible) will - that will come out very soon; it's
a very involved data analysis process, it's literally terabytes of data
in that VLBI cross correlation. So that's been taking a little bit of
time.

Okay, so if we go on to the next slide. In Europe, at least this was big
news, I mean, Europe has flown planetary missions before \-- Giotto
maybe 20 years ago went to Comet Halley; Mars Express, of course is in
orbit around Mars and delivered the Beagle 2 probe which sadly was lost
without trace. But the Beagle 2 exercise really sort of woke up the
European public and maybe the politicians too to the excitement and
benefits of space exploration, and that seems to be reflected in at
least a couple of the European member states where the Huygens
investigators got some attention from the high-ups.

This picture here of John Zarnecki, my old advisor at the Open
University, the research group at the University of Kent where I did my
PhD actually moved en masse to the Open University in Milton Keynes.

There's a very Orwellian kind of posture or something of John Zarnecki
in the background but he's presenting Tony Blair with a little
certificate or something.

Jacques Chirac invited several of the French Huygens participants, the -
including the project scientist, Jean Pierre Lebreton to the Elyseés
Palace and I think maybe Jean Pierre is eligible for Légion d'honneur or
some big honor like that.

So here in Tucson, we're still waiting for our call from the White House
but no luck yet.

Anyway, the things I'd like to talk about today are to talk a little bit
about the Earth based observation, give a sort of overview of the Nature
papers, I mean, even though the first results summaries in Nature are
supposed to be written for a pretty wide audience and are. There's an
awful lot of information in there and it's probably worth my going over
some of the material just to put in context.

There's some of the engineering data from the probe I'd like to get
involved in. It's really rather fun trying to sweat out scientific
results from what superficially is really quite dirty, unexciting,
ill-conditioned kind of data \-- data that was never intended for
scientific analyses but actually does provide information on the Titan
environment. One of those is from the signal strength of the radio
transmitters on the probe and another is the temperature history of the
probe.

And then finally, I'll talk a little bit about the sort of surface of
Titan and how the probe's results changed our perception of what Titan
is like, how it's matching up with results from the radar.

So the next slide shows a sort of montage of three radio telescopes from
top to bottom. There's Green Bank in West Virginia or Virginia, I can't
remember which; Parkes in Australia; and the much smaller dish at Kitt
Peak about 60 miles from where I'm sitting now.

The globe is \-- the Earth as seen from Titan during the probe - at the
probe landing; you can see the sub-Titan point at different times
marked. So the Earth is rotating underneath Titan if you like and that
shows where the Earth was - where vertically above the Earth was Titan.
So at the beginning - at entry, Green Bank in West Virginia was pretty
well posed to observe Titan and Huygens. And then by the time of the
landing, the Earth had rotated around to the point where Titan had set
as seen from the Eastern US. Kitt Peak was still observing. Parkes in
Australia had just picked up the probe.

The probe continued to transmit after it landed. It landed after 2 hours
and 28 minutes of descent. The descent was supposed to be normally 2
hours 15 minutes plus or minus 15 so it only just squeaked under the
wire. We're not sure whether that's due to slightly higher drag
coefficient on the parachute than was expected or whether the atmosphere
was slightly different from the nominal model. It was pretty close to
nominal model. So that's still being worked.

If the probe had taken another two minutes to get down to the ground,
some of the investigations would actually have been lost. There was a
timeout on the Surface Science Package for example. You know, the probe
is sort of like falling with your eyes closed, you don't know where the
ground is going to be and especially if you take into account the
possibility that some systems may fail.

You know the impact accelerometer and the penetrometer was sort of you
know, held out waiting for impact. But, you know, what if something had
gone wrong with them?

We wanted to change into a surface monitoring mode once we were on the
ground but with a timeout in case something had gone wrong with the
penetrometer and we didn't detect the impact, we still want to switch to
a surface mode and that was programmed to happen after 2-1/2 hours, you
know, to get - by then it should be down on the ground whether the
impact was registered or not and had we done that we wouldn't have
recorded the impact event itself. So that was a little bit of a close
shave.

On the Surface Science Package team we had a little sweepstake running
on the descent duration. I think I shot for 2 hours 22 minutes but John
Zarnecki guessed closest and won a very nice bottle of scotch as a
result.

On the left of the plot there is a frequency spectrum. So you can see
the noise level, and there are very clear spikes sticking above it. That
was the really great news we had. It's around about 11:30 or something
on the morning of the 14th that the Huygens signal had been detected on
the ground.

This \-- the radio astronomy exercise had two real purposes: one was to
monitor the Doppler effect, which was going to be done onboard by
Cassini, but by measuring the Doppler shift from the earth as well as
from Cassini, we measured the Doppler shift in two directions so you get
the range rate or the velocity along two independent vectors and that
makes you start solving for whether the motion of the probe was only in
an east-west direction or whether it was a north-south drift.

Now using the same telescopes but with different receivers, this
entirely a separate experiment VLBI wherein instead of measuring the
motion of probe along the line of sight, you measure the angular
position of Huygens in the sky by comparing the phase of its
transmission to the phase of astronomical sources. We actually had to
observe a number of - sort of calibration targets, quasars, and things
to figure out the exact position on the sky.

Now in principle that may give us a resolution down to a few kilometers
and again will be very good in terms of identifying the winds that we
only have one component from the Doppler.

Now the probe continued to transmit after it landed on the ground. We
got signals on Cassini, until Cassini sets about just over an hour after
landing. And what the probe continued to transmit because we know
because we're listening with these radio telescopes on the ground. You
can see some little red triangles in Japan and China, those received the
signals, I think, up to about three hours after landing.

And then there was a scramble to try and set up more telescopes because
nobody had expected the probe to survive so long.

Now the Huygens transmission is on a relatively unusual frequency so
that you need special receivers, special polarization \-- one thing to
get the polarization right is the feed that the focus of the antenna has
to be oriented a special way. And apparently there were a couple of guys
in Finland were up on the dish, you know, manually rotating this feed in
the middle of the night. You know, it's pretty cold up there to try and
to pick up the Huygens signal, but unfortunately, they didn't detect it.
But modeling the performance of the batteries, we think the probe kept
working for at least 15 minutes after the last signal we received; so it
really did pretty well.

You always have to be conservative when designing for an unknown
environment. You don't how well batteries are going to perform after 7
years in space. You might make the assumption that the battery may fail,
that the cells in the battery may fail or that some experiments may fail
in such a way that they draw more current than they're supposed to. So
there's some margin in the battery design.

As it turns out, during the cruise to Titan, the probe was a few degrees
cooler than the specification of the model and so the batteries were
preserved rather better. And then during the descent itself, the probe
was actually warmer by a few degrees and that also helped the battery
performance. That's why the probe lasted so long. There were some
built-in margins which were not needed because none of the batteries
failed and basically everything worked in the batteries' favor.

The same was not true, as you may have heard, for the performance of the
radio system. There were two entirely independent data channels \-- I
mean, a separate computer, a separate radio transmitter on the probe,
and two separate receivers on Cassini and nominally they're supposed to
carry the same data at the discretion of the experiment but staggered by
10 seconds. The reasoning being that if the probe were to experience
violent attitude motion, swinging on the parachute, then you might lose
the link for a few seconds.

But if you have the same data being sent in a staggered fashion then you
can kind of patch across the gap because you have a separate copy of
information that was transmitted 10 seconds ago so even if you loose 8
seconds of data you can still patch across that gap.

Now some of the experiments used the two data channels to send extra
data so - but it wasn't duplicated and that was of course a gamble, a
perfectly reasonable gamble to take. But in the end, it turns out that
there was a command omitted on the receiver on the orbiter. I mean,
there are two separate receivers. One of which was configured to do the
Doppler measurement and so it has a specially stable clock, an ultra
stable oscillator, with which to compare the received signal frequency
and thereby measure the Doppler shift very accurately. And as though the
receiver was selected to use that ultra stable oscillator, the
oscillator was not powered on. And so all that data was lost the entire
Channel B \-- sorry, channel A (unintelligible) was lost entirely.

Fortunately, because there was this supplement to the Doppler experiment
by doing the ground base detection, most of the Doppler information is
recoverable. It's not quite as extensive or as gap-free as the
measurements on Cassini would have been. But most of the goals of the
experiment were met.

It's worth remembering that the transmitter is only 8 or 20 watts. So
from a billion miles away, it was really quite an impressive feat to
detect the signal. Unfortunately, you can't recover any data from it,
but you can see that the signal is there and measure its frequency.

There was maybe unintended feature of the probe transmitter design and
that is, as well as the modulated subcarriers that carry the data, there
is a little bit of radio signal coming out from the antennas that's pure
carrier, it wasn't modulated with any data and that's actually what the
Doppler experiment used to track, and the existence of an unmodulated
carrier makes this sort of experiment much, much easier to do.

When they tried this with Galileo which was, you know, twice as close to
the Earth as is Saturn, it was actually a lot harder because it didn't
have this unsuppressed carrier.

Okay, the next slide shows something that you probably haven't heard
much about because it didn't really come to pass. Some years ago, I seem
to remember Jean Pierre Lebreton, a project scientist, suggesting that,
you know, it might be kind of interesting if we could see the sort of
meteor trail from Huygens as it landed. You could think of it as a 200-
or 300-kilogram meteor which is quite a good size.

Now the SL9 comet that smashed into Jupiter in '94 and was easily
observable from Earth but of course orders of magnitude bigger. I mean
it was, you know, kilometer-sized chunks of ice. That's easy to detect
as much smaller objects like Huygens so far from the Earth would be -
was really pushing the limits of what's possible.

But it was one feature which was a little bit on the favorable side
which is in an atmosphere that's rich in carbon and nitrogen like
Titan's methane-nitrogen atmosphere you get a very strong violet
emission from a carbon-nitrogen bond in the shock layer. You know, when
a gas is heated to thousands of degrees by the passage of the probe, you
know, hypersonically through it, it has a reddish glow but also is very
strong violet and that violet emission is very narrow wavelength region,
you can sort of see the spike on the spectrum there at 387 nanometers.

So knowing that was there, some calculations I did show that in
principle it might be detectable \-- I mean, it was kind of a long shot.

Now as it turns out, the ideal instrument to make this observation was
the space telescope imaging spectrometer on Hubble and it was the very
first HST proposal that I successfully made; I've made a number of
proposals that weren't selected in the past. HST is over-subscribed by a
factor of about 10 to 1. So even you have a good proposal, your odds are
not great at being selected. But this observation was clearly special
and was selected.

But after we made the all the observing plans together, the instrument
failed in orbit last August \-- sorry, not last August, August 2004. And
so, the observation had to be deleted; it was a great pity.

Some of the other telescopes that were observing Titan during the entry
event, unfortunately, the Hale telescope which was going to do violet
spectroscopy as well was clouded out.

It was horrible weather in Hawaii. I was is on the phone on the morning
of the 14th, the morning European time that is, to folk over in Hawaii
trying to observe and they had snow and wind. I think the Gemini
telescope couldn't even open their dome, the conditions were so bad.

In the end, IRTF and , I think, Keck did squeeze off a few pictures, but
the wavelength they were observing, there wasn't really as much emission
from the entry fireball or the entry meteor trail so that only
established some upper limits on the emission, which would have been
kind of a fun thing to detect but not really central.

There's also a sort of forensic astronomy aspect to it in that say we
had never heard from the probe, you know, Genesis - the Genesis failure
where the parachute didn't come out, was only a couple of years ago.
Beagle was lost. So it's not without precedent that things can go
horribly wrong and you want to know why they went wrong.

And with these probes it's often the case that just there's no
information to go on, you know, had we missed Titan altogether or had
the probe arrived but not deployed its parachute. If, you know, if we
had detected the entry signature then we'd know it at least, you know,
had arrived at the right planet at the right time and that something
else was the reason for the failure. So it's still worth doing. It would
have been quite a fun thing to interpret but, as I said, the
observations didn't quite pan out. But there was a lot more activity
than just what was going on in Darmstadt.

Man: Could I ask you a quick question, what about using Spitzer?

Ralph Lorenz: Spitzer, I don't know if anyone thought of using it. Was
it even operate-operating then?

Woman: (Unintelligible).

Man: Yes, I believe so and it's infrared, but just a question.

Ralph Lorenz: Yeah. You can see that the shape of the spectrum
(unintelligible) was longer wavelength.

Man: Uh-huh.

Ralph Lorenz: It might be that it would be a more sensitive \-- I don't
know if anyone looked at it, to be honest.

There was a 10-micron spectroscopy done on IRTF by Henry Roe and he
didn't see any evidence of a spike. But yes, Spitzer might have been
worth trying \-- that's \-- well, next time.

Okay. I guess I've got plenty of time, so it's okay to dwell on these
things. But we have the next slide we can see what the probe was doing
during its entry.

It was, you know, switched on four hours before entry just to warm
things up to get the clock to drift in the right direction. But during
the entry itself, the probe's computers were all powered up and the
Huygens atmospheric structure instrument was observing.

Basically, it has a very sensitive accelerometer, I mean, the kind of
thing that's used in, you know, car to actuate air bags, you sense how
quickly you change speed. But this is a much more sensitive device than
is used in cars for airbags because the 20G peak deceleration which is
more which was more or less the same as the impact deceleration in
Huygens at the ground, it's kind of the fender bender sort of level. And
that peak deceleration occurred at around, I think, 350, 400 kilometers
altitude.

But with a much more sensitive accelerometer, you can feel the
atmospheric drag on the probe much higher up. And in fact this I think
is the most sensitive accelerometer that's been flown on a planetary
mission. There have been Earth satellites and Earth entry vehicles that
have used more sensitive instruments but, you know, we picked up the
atmosphere at about 1500 kilometers where we had a few micro G of
deceleration.

And Cassini is flying down to 1200 kilometers or a little bit lower. So
there's a very nice overlap between the in-situ measurements that
Cassini is making as it flies to the upper atmosphere and the in-situ
measurements that the probe made.

Now you can see that the temperature of the upper atmosphere, the solid
line that's inferred from this deceleration record is a little bit
warmer through most of the atmosphere than the model. The model had
this, which is the dashed line, had this big dip. The mesosphere where
emission of infrared radiation by optically active gases like hydrogen
cyanide, which is supposed to cool the atmosphere, but I guess it was
being warmed a little bit more than had been expected. That was a major
finding.

You can also see these big spikes. Those are believed to be gravity
waves. Basically, as, you know, activity in the lower atmosphere kind of
pushes the atmosphere up and down a little bit, these waves propagate
upwards and can be seen is scintillations and the stellar occultations
that were done from the ground where you see the light from the star get
bent by the atmosphere, the atmosphere acting kind of like a lens. And
you can see fluctuations in the brightness of these occultations and
those are due to the temperature variations associated with gravity
waves.

So those were being looked for and they show it very clearly in this
deceleration record.

The lower part of the atmosphere below, you know, 150 kilometers or so
where the atmospheric structure instrument measured pressure and
temperature directly with, you know, pressure and temperature sensors.

You can see the model is exactly underneath the data \-- I mean, the
model which was based on Voyager radio occultation back from the 1980s
was bang on, I mean, the atmosphere is exactly as predicted in that
respect.

Okay, so that's the main (unintelligible) result.

The Doppler wind experiment using the ground based results \-- most of
the solid line there is Doppler measurements made by the Green Bank
telescope. There's a little gap during the changeover to Parkes in
Australia after Green Bank had set. And there was a model that we, you
know, designed the probe to, the expected wind drift by Mike Flasar
based on Voyager infrared measurements.

And you can see in big picture sense, the magnitude of the wind was
pretty much as expected, you know, you always allow a variation because
you're not sure the model is right and that envelope is defined by the
dotted line. And you can see virtually everywhere the measured profile
lies within the envelope; so it was a pretty good envelope to design to.

In the lower atmosphere, especially though, you can see that the wind
drift was rather less than predicted, so definitely worth making the
measurement. And we have to revise our understanding a little bit of
Titan's wind environment.

But also, not completely unexpected but fairly unexpected, is that the
shear layer at around 80 kilometers, you can see the winds drop almost
to zero, which was really quite a striking result and I guess people are
working to explain that.

There is, you know, a big difference between the Earth's atmosphere and
Titan's atmosphere and that is the thick haze absorbs a lot of sunlight
at high altitudes, I mean, that's what creates Titan's stratosphere in
some sense in much the same way as absorption of ultraviolet light by
ozone in the Earth's atmosphere creates local heating which gives you
the stratosphere. But the absorption of sunlight is much more strong in
Titan's thick haze.

So, you know, if you absorb a lot of the sunlight high up than that
deposits energy which goes into driving the wind. So whether that
80-kilometer layer is associated with some change in the haze density we
still need to figure out.

One real surprise, I guess, is that little blip at the bottom, you know,
with the Parkes area reporting into it that the wind reversed in
direction. We would expect from we knew that Titan's winds were
pro-grade going west to east in the same sense that Titan rotates. But
it seems that near the surface there's a little bit of a reversal.

There's a really interesting effect that maybe peculiar to Titan and
that is that near surface winds may be dominated by the gravitational
tide due to Saturn. The orbit of Titan around Saturn is a little bit
elliptical, so the tidal - the strength of the tidal force is very once
per, you know, once per 16 days and that may lead to periodic wind
pattern near the surface which may drive all kinds of things like
formation of sand dunes, but that may be hardly responsible for the
reversal in wind direction near the surface. But that was really quite a
surprise.

Going on to the next slide. This is some work I've been doing, trying to
understand what the shorter term motion of the probe was.

If you go onto the next slide, I'll hope you'll agree that these two
data sets look superficially similar and that's because in a dynamic
sense, they are. One is the measurement of a little accelerometer on
Huygens probe. It was actually designed to measure the probe's spin
using the centripetal acceleration due to a spin. But it recorded
basically a whole sequence of more or less random motions.

And a probe suspended underneath the parachute is in some sense much
like a pendulum and a lot of seismometers are exactly that a weight
first position is monitored relative to the ground. So dynamically it
also is like a pendulum, and that's why these two data sets look a
little bit similar. You're basically forcing a pendulum with a pseudo
random sequence of impulses.

Now, it's not true to say that Titan was gusty with the results of this.
Some of these motions are probably self-excited by the unsteady
aerodynamics of the probe itself. I mean it's a blunt body and not a
very streamlined body and you may get vortices being shed asymmetrically
from the trailing edge of the probe; they call it a sort of side-to-side
buffeting and that's I think what is causing most of the signal here.

But you can see at the beginning it's rather quiescent that was when we
are the under the big main parachute which was about 8 meters in
diameter. The reason we have such a big parachute is so that the front
shield - the heat shield can fall away safely with the probe held up by
the big main parachute. But with that big parachute, we take five hours
or more to get down to the ground by which time Cassini would have
sailed over the horizon and would have lost the link.

So we have to switch to a smaller parachute called a stabilizer or a
drogue. And at the moment that happens you can see the - after 10
minutes, you can see the amplitude of the acceleration grows
substantially and that's not necessarily because the parachute is
unstable as such but just we're flying much faster through the air and
so there's stronger buffeting of the probe itself.

But the profile doesn't fall off sort of gently like a decay you would
expect if the buffeting were only proportional to the descent speed. You
can see it kind of declines and grows and then declines again.

So some component of that is probably associated with the Titan
environment. We're still trying to understand exactly how much is
self-excited and how much is driven by the wind.

The motions get a lot less when we got below about 20 kilometers
altitude that may be where we cross the coastline or, you know,
something that looks like a coastline in the images which I'll get back
to later.

But \-- so there's pretty rich data set here. It's really crying out for
further analysis. It's difficult to interpret without more very
expensive tests like wind tunnel test or parachute drops; but we're
doing the best we can.

Generally, this sort of data isn't really studied much. There's lot of,
you know, parachute borne probes to Mars. But in the Martian atmosphere,
which is very thin, you get down to the ground in just a couple of
minutes and so these data sets aren't very long and there's usually lots
of things going on like parachutes coming out and airbags being
inflated, and so there's lots of engineering events that contaminate the
record. So nobody's really looked at this kind of data very much but
it's something I'm hoping to do a little bit more in the coming months.

Okay. Next slide is atmospheric structure instrument again.
(Unintelligible) you can really match these data up very well with the
pre-Cassini models but those models, though they were right, have very
large uncertainties.

We didn't know whether there might be a few percent of argon in the
atmosphere which changes its molecular mass and therefore what the
surface temperature you'd infer would be and so we didn't know for sure
what the surface pressure and temperature was going to be - to within
maybe 4 or 5 Kelvin with sort of range of uncertainties. But the HASI
temperature sensors show it very clearly the air temperature near the
surface was just under 94 Kelvin and the pressure was just under 1.5
bar. So a combination of those two makes Titan's air density about four
times that of sea level air on Earth.

We identified the tropopause more or less where the models had it
70 Kelvin, 44 kilometers.

Now the rather garish looking part on the right, this is an instrument
called a relaxation probe. Basically, it's a disc of metal that is
energized to a specific voltage and then you observe how the voltage
decays, basically, how the charge leaks away as if it were just a big
capacitor. And that indicates the electrical conductivity of the air
which can depend on lot of things but one key thing is ionization by
cosmic rays. That occurs in the earth's atmosphere at several kilometers
altitude but it's fairly close to the ground.

Because Titan's atmosphere is so thick, all these cosmic rays get
deposited around 60 or 100 kilometers in altitude. And in fact, just
like in the Earth's atmosphere, these cosmic rays will not only produce
some ionization but they'll also produce radio carbon. The cosmic rays
will interact with the nuclei of nitrogen and Titan has a lot of
nitrogen in its atmosphere to make Carbon-14. And Carbon-14 is, you
know, radioactive itself and decays with a half life of 7000 years or
so.

So it might be that this radio carbon gets stuck into Titan's haze and
makes the haze a little bit radioactive and maybe on a future mission we
might be able to date how old organic material on surface is by radio
carbon.

But certainly the cosmic ray deposition seems to be more or less exactly
where it was predicted to be and forms this ionization which gives the
electrical conductivity which is seen in the bottom there.

There wasn't any obvious signature of lightning. I know there's been
occasional mention of something or some sort of electrical discharge one
moment during the probe descent and in fact one part of the GCMS
instrument stopped working at that point \-- one of the \-- you have
five different ion sources and one of those five stopped working at that
point. And it's not known whether maybe there were some sort of charge
build up on the probe that discharged or whether what's interpreted as a
discharge is actually an effect of a small failure in the instrument
or - that's still being worked out. But the overall results from the
GCMS instrument weren't significantly impacted.

Trina Ray: I'm sorry to interrupt, Ralph, is that music on your end or
is it someone else?

Ralph Lorenz: It's someone else.

Trina Ray: Okay. I'll go off to the operator and see if they could track
it down.

It's kind of nice.

Man: Could I ask about the lightning, has that been detected by Cassini
at all or you have no evidence for lightning at all?

Ralph Lorenz: There is, as I understand it, no evidence for lightning.
The radio and plasma wave system on that Cassini orbiter has been
listening for it whether they have signals, they are still working on
that could be interpreted as lightning, I don't know, but certainly
there's been no pronouncement.

I actually did the lightning hazard assessment to the Huygens probe, you
know, it's one of those little jobs that as, you know, a fresh kid
straight out of college got to do on the Huygens project which is, you
know, staffed by senior engineers who've worked on satellite projects
for decades but satellite projects don't have to worry about such
things. Huygens was a genuinely new thing to be doing. So a question
came up do we need to protect against lightning. So I looked into it and
some specifications were developed for what kind of current pulses would
have to be tolerated.

And so the probe \-- I mean, the probe is more or like Faraday cage.
It's a metal box, and it does actually have three little wicks, little
conductive stalks that allow the charge to (unintelligible), the same
thing that we used on Concorde actually. And this is a very common
problem for aircraft, you know, if you fly through clouds, the cloud
droplets can be charged and so that charge can build up. And during the
early days of aviation, when people had rubber tires on their plane
they'd get an electric shock when they climb out and so they started
realizing they should use metal skids.

There was a big test done in '94 where they had the Huygens probe in a
room with a huge (bandy graph) generator that, you know, generated, you
know, some couple million volts or several hundred thousand volts and
discharged again to different parts of the probe and the probe just kept
working fine like it was supposed to.

Now all the test equipment that was monitoring the test in the next room
that all failed and had to be rebooted when this discharge occurred. But
the probe itself was pretty well-protected. I mean electromagnetic
compatibility and resistance to interference is something that
spacecraft electronics often have to be designed to and the probe is
pretty robust.

Man: Did you expect lightning there or not?

Ralph Lorenz: No, I would not.

Man: Oh, you did not.

Ralph Lorenz: The reason being several-fold. One, there's simply not
much cloud activity. We're seeing some now, from the ground and one with
Cassini, but it occupies, on average, maybe only a percent of Titan's
surface area compared with maybe 30% on Earth with much less sunlight to
drive violent convection.

Then there's a separate question of how you accomplish the charge
separation process which isn't that well understood on Earth, to be
honest. It benefits from water being a polar molecule so that you can
accommodate fairly high charge densities without the droplets breaking
up and basically you can make good capacitors out of water.

Methane is a much poorer dielectric. So methane drops would start
tearing themselves apart if they got charged up substantially.

So because of the lack of sunlight driving them, because the lack of
evidence for lightning, and because methane is not a good charge
separator, I argued we probably would not encounter lightning.

But the HASI instrument had electric field sensors that were listening
for lightning discharges and certainly nothing obvious was detected.

Okay, the next slide is on the Aerosol Collector and Pyrolyser. This
thing is like a sort of a vacuum cleaner. It sucks in the air with a fan
and sucks in through a metal filter and the aerosol particles get
trapped on that filter and then the - that's also pulled inside the
instrument into an oven which is then closed and then heated up to about
600 Celsius and the gases that come off were passed into the gas
chromatograph mass spectrometer for analysis.

And you can see there's, you know, a lot of background signals. It's a
good lesson you need to take these sort of background measurements. But
one very prominent thing has basically no background associated with it
(mass 27) which is related to nitriles and that really shows that the
haze particles are not just hydrocarbons, not just molecules with carbon
and hydrogen, but they incorporate nitrogen in them too.

Now, most of the chemistry on Titan is probably driven by solar
ultraviolet light and that's pretty effective at breaking the
carbon-hydrogen bonds in methane.

It's much less effective at breaking the nitrogen-nitrogen bonds and
molecular nitrogen. That's a very strong bond and requires very short
wavelength UV of which there isn't much to go around.

So the fact that haze incorporates a lot of nitriles it seems is
consistent with the idea that there's another energy source for some of
the photochemistry and that's probably magnetospheric electrons, you
know, trapped electrons in Saturn's magnetosphere being dumped at the
top of the atmosphere. That probably occurs higher up than most of the
UV absorption.

So the different energy sources contributing to Titan's photochemistry
at different altitudes and somehow that all gets folded into the complex
chemistry in the haze but the ACP really shows that there's a lot of
nitriles in there.

The haze, incidentally, over geologic time may have been an appreciable
sink for nitrogen. Nitrogen doesn't escape Titan's gravity very easily
but there's certainly the indication that Titan has lost a lot of
nitrogen over the years and one of those sinks may be the - into the
haze.

Just as an aside, one of those things that we wish we caught better was
the fan on the Aerosol Collector and Pyrolyser. It turns out to have
made a lot of noise. And there's an acoustic experiment on the Surface
Science Package, little sonar to measure the depths of an ocean if we
landed in an ocean to measure the presence of cloud droplets if we or
raindrops if we flew through those.

But that little echo sound was completely swamped by the background
noise when this fan was switched on, just one of those experiment
compatibility things that didn't get adequately addressed.

Moving onto the Gas Chromatograph and Mass Spectrometer, you can see
here an average spectrum at high altitude and you can see \-- this is
just in raw account so you can't use these as relative abundances
directly.

You can see there's argon-40 there, there's CO2. There's actually not
very much CO2 in Titan's atmosphere, a few parts per billion, some of
that signal there may be background from the instrument.

There's some argon background as well and in fact what happens is you
use argon in welding and when the pipe work and instrument gets welded
together there's a little tiny bit of argon that gets stuck in there
that gets - that slowly leeks out even (unintelligible).

But the instrument did detect an isotope of argon that's produced by the
decay of potassium, radioactive potassium in rocks. And the fact that we
see this radiogenic argon means that somehow the rocks and, you know,
from Titan's mass, we think it's roughly 50/50 rock and ice.

But all the rock probably sank to Titan's interior early in its history
to form a rocky core. But the fact that there's radiogenic argon in the
atmosphere it means that gas released in the core has at some time been
able to get out to the surface into the atmosphere. So that's certainly
consistent with there being volcanic activity on Titan. There's not at
the present then at least in the past.

It doesn't absolutely mean it. You know, maybe the gas leaks up through
some kind of cracks but it's certainly consistent with it.

There's hardly any primordial argon. There's a regular isotope of argon,
argon 36.

Now, that isotope of argon has a similar molecular mass to molecular
nitrogen. So if Titan's nitrogen atmosphere were brought to Titan as
molecular nitrogen you'd expect to find a lot more argon 36 because of
the same sort of volatility. If the nitrogen was trapped in ice, for
example, then argon 36 would also be trapped in the ice and would
release - would be released into the atmosphere with the nitrogen.

The fact we don't see this argon 36 suggests that the atmosphere was
brought to Titan as a different and less volatile species probably
ammonia. There's cosmological argument for suggesting that ammonia would
have been present.

And ammonia is very interesting in terms of cryovolcanism and that it
acts as an antifreeze. If you make a 30% solution of nitrogen - of
ammonia in water, it has a freezing point of 176 Kelvin rather than 273
for plain water. So it acts as a very good antifreeze, meaning, you
know, the cryomagma can be a liquid at much lower temperature than pure
water would.

There's also the fact that a strong ammonia solution, actually ammonia
dihydrate is the compound that's actually formed, it has a density
that's comparable with that of ice, about 900 kilograms per cubic meter.

You may \-- we'll be aware that water in liquid form is a bit more dense
than ice. So if you had water as a cryomagma it will be difficult to
make it go to the surface because it would just want to sink, wouldn't
want to come up whereas with the ammonia dissolved in there, it makes
the material much more buoyant or certainly much less unbuoyant, let's
say.

So that all sort of hangs together that there's a lot of ammonia perhaps
incorporated into Titan. When it formed, much of that ammonia was
converted into molecular nitrogen to form the atmosphere we see today.
But much of it may still remain dissolved in a liquid layer in Titan's
interior, probably 50 or more kilometers beneath the surface so not as
close to the surface as the water ocean on Europa, for example, but
maybe more extensive and maybe more rich in other material.

The isotope ratio of carbon 12 to 13, there's not enough radiocarbon to
detect with this sort of instrument is - the ratio is enriched compared
to the sun, for example, but it's not very heavily fractionated.

In fact, it was thought from measuring the abundance of HCN, hydrogen
cyanide with carbon 13 versus carbon 12 because HCN is a very
radioactively active molecule. It's a polar molecule that has some very
distinctive molecular emissions in the millimeter part of the spectrum.
And from Earth you can measure those emissions and discriminate the
carbon 12 from the carbon 13 in HCN and that suggested that the nitrogen
was very strongly fractionated meaning that maybe Titan had loss 30 or
50 times its present inventory of nitrogen sometime in the past. Maybe
this was during a violent phase of solar winds early in the solar system
history when the strong solar wind would basically sputter away a lot of
the atmosphere and would preferentially sputter away the lighter
isotopes.

But with the GCMS instrument in-situ, we could measure the nitrogen
enrichment in - molecular nitrogen, not HCN, sorry, I spoke - I mean I
said they measure the carbon.

So, it's very important to get that enrichment number for nitrogen in
molecular nitrogen, nitrogen not a radioactively active gas. You can\'t
measure it from Earth - so we really that in-situ measurement.

So it says that there wasn't as much fractionation as it previously
been. There's - I mean the HCN measurement that have been done from the
ground was correct but there's only a very small amount in the total
nitrogen inventory on Titan tied up in HCN, most of it is in molecular
nitrogen. So this new measurement is much more useful in terms of
understanding the evolution.

The similar enrichment in - here in the hydrogen ratio that had been
known also from spectroscopy from space in fact. And it's probably
related to photochemistry.

So it may be that the photo chemistry is also what enriches the heavy
nitrogen isotope in HCN that it's not peculiar to the total nitrogen
inventory.

So you need these - and maybe just individual numbers, you know, a ratio
but they are crucial in understanding Titan's history. So these are some
key results from the GCMS.

I don't believe there's been much in a way of molecules discovered with
the GCMS that weren't known to be there that requires really
understanding some of those small pieces just above the background. So
that will take a lot of work and probably laboratory testing to fully
understand it.

Man: Is there any information on the composition of those compounds that
we do know?

Ralph Lorenz: Any information on the composition of the...

Man: I mean the amount, I\'m sorry.

Ralph Lorenz: Oh. Yeah, I mean there's a table in Lifting Titan's Veil.
And some of them are present at very trace levels. Carbon dioxide is, I
think, 10 ppb, you know, parts per billion.

Man: Right.

Ralph Lorenz: They're - you know, roughly, we now know what the methane
abundance is. It's about 1-1/2% in the stratosphere, rather more near
the surface. That was previously unknown to - within a few percent.

The next most abundant is hydrogen which is at around a tenth of a
percent. And then, I think, ethane is down at few hundreds ppm. And then
from there on down, it's parts per million or parts per billion. I think
20 compounds have been identified, the biggest being benzene at this
point, I think.

There are molecular emissions that are being observed by the Composite
Infrared Spectrometer on Cassini. There are all kinds of peaks that will
come out of the noises as their data builds up over time. And some of
those peaks are probably not yet identified. But there are things like
methyl cyanide or (unintelligible), dicyanide nitrile, whatever the
official name is. CH3CN...

Man: Acetonitrile.

Ralph Lorenz: Okay. That's not the International Union of Pure and
Applied Chemistry name.

Man: A chemistry name.

Ralph Lorenz: It seems to be everyone uses the archaic terms.

Man: Right.

Ralph Lorenz: So yes, so they go down to the parts per billion level.

Man: Uh-huh.

Ralph Lorenz: The Ion and Neutral Mass Spectrometer on the Cassini is
also recording species with molecular masses up to - and beyond 100, I
think, but identifying those will be quite a challenge.

Man: So above 1%, there's only nitrogen and methane. Is that right?

Ralph Lorenz: Correct.

Man: Okay.

And ammonia has not been directly detected yet, is that correct?

Ralph Lorenz: That's correct. Ammonia was actually a real puzzle, you
know, Saturn system wide. We didn't expect to see it on Titan anyway.
Titan is so cold that vapor pressure of ammonia is tiny and it's like
CO2 to first order. But I don't believe any - ammonia would detectable
even by the GCMS.

There is the question of what about the ammonia in the ice.

Man: Yeah, that's the one I was just going to ask.

Ralph Lorenz: That's an interesting story and that ammonia is destroyed
by ultraviolet light to a similar extent as methane. So anywhere where
ammonia in the ice would be visible to a spectrometer, it's in
principle, also visible to the sun which would destroy it.

Man: Uh-huh.

Ralph Lorenz: So you'd need some fresh exposure, you know, like, say, an
impact crater that threw out some ice that hasn't had time to be
destroyed for the ammonia to be visible. But as I understand it,
nobody - and the VIMS team I guess are the key players here, the
spectral signature of ammonia has not been unambiguously detected on the
surfaces of the Saturnian satellites.

There was another effect which is one I got involved in which is that
ammonia is a strong microwave absorber. You only need to add a little
bit of ammonia to ice to make it much less radar transparent, very cold
ice, you know, far below the freezing point is very transparent to radio
waves and microwaves. You can verify that by taking some ice out of the
freezer and put it in your microwave oven, you'll find the ice doesn't
warm very quickly.

We did an experiment - so far, I believe the only published microwave
(unintelligible) experiment on ice were done in my wife's microwave
oven. I took some ammonia-doped ice and put it in the microwave. And it
melted very quickly.

Man: Uh-huh.

Ralph Lorenz: Ammonia is a very strong absorber.

So that - the presence of ammonia may affect the radar reflectivity,
microwave emissivity of surfaces in the Saturnian system. And you see a
very pronounced trend of those properties as you go from Mimas, you
know, close to Saturn out to Phoebe. There's basically a consistent
gradient in microwave emissivity as you go out from Saturn.

So that's just maybe a compositional gradient specifically in the
abundance of some microwave absorber which may be related to ammonia.
Maybe it's related to HCN and some of the other nitriles, we don't know.
But there's certainly a gradient in microwave properties that probably
is related to a composition gradient.

Man: How about the cryovolcanoes, can you direct the instruments to that
area and look for ammonia there?

Ralph Lorenz: Well on Titan, it's pretty difficult because there are
only a few selected windows through which we can observe the surface
from orbit. Methane absorbs a lot of the near infrared light.

So you only have a little tiny bit of the spectrum to work with which
makes it very difficult to identify the spectral signatures of ammonia.
You need to see a set of, you know, absorption bands related to ammonia
which, you know, may or may not be that obviously distinct from other
compounds that may be in (unintelligible) ice.

Since you only have this list of jail bars of the spectrum to work with,
I think it's going to be a real challenge to identify ammonia on Titan's
surface.

Elsewhere, you know, as I say, it needs to be fresh. Well, whether it's
fresh cryovolcanism or a more freshly exposed surface on other way. I
think I wouldn\'t be at all surprise if it - dusty things should be
discovered. It's not likely to be discovered on Titan, I think.

Ralph Lorenz: Okay. I better move on to the next slide.

Trina Ray: I was going to say, Ralph, I don't want to interrupt or
anything but you've got about 45 minutes before - where you run out of
time, although I\'m sure they'd let us go a little bit longer. I just
wanted to let you know.

Ralph Lorenz: Okay, thanks.

Trina Ray: Okay.

Ralph Lorenz: The next slide is not really much to say about. It's -
basically if you collapse an image on to a line, basically add up all
the pixels in each line and then make a graph of the total versus line
number, and basically, you'd get a very high signal to noise measurement
of the brightness in the image.

And there's an indication here. This is the side-looking image on the
Huygens probe. There's a little - indication of a little thin wisp of a
cloud here, you know, not more than a percent or so brightness
variation. But there was a thin cloud layer.

Now, that 21-kilometer altitude is sort of interesting, in that, that's
not - there's not a very sharp boundary but it's roughly where the
decent became a lot more quiescent judging from the accelerometers on
the probe.

Now, whether that is a cause or an effect isn\'t obvious.

There is also the issue that's more or less where we cross the
coastline. So whether it's a case of, you know, sea breeze circulation
causing some condensation or maybe the - as the airflow hits the hills
or the coastline, whatever you want to call it and rises, there's a
little bit of a fog formed. These are things that will take a while to
disentangle the chain of cause and effect.

Now, on to the next slide, this is the methane story.

On the top chart is the Gas Chromatic Mass Spectrometer result. And, you
know, we knew there was roughly 1-1/2% to 2% methane in the
stratosphere. That's relatively easy to - there are spectral regions
that are easy to analyze - to recover that from - both Voyager and CIRS
data.

But in the troposphere, understanding the methane profile near the
ground is much harder. And the numbers - talked about in the literature
vary by a factor of (unintelligible).

And we can see as we go below 40 kilometers down into the troposphere
that the abundance goes up consistent with there being a source or a
reservoir on the surface. It's very similar sort of profile to water
vapor in the Earth's atmosphere; or be it, the water vapor is - in the
Earth atmosphere is more like a percent rather than 5%.

But it similarly decreases with altitude until you get to the cold
trap - the tropopause and then it gets pinned to that cold trap value.

Now there's - the inset there shows how the methane abundance really
sort of takes off at about 16 kilometers. Honestly, it wasn't quite
saturated at that level but it was very - it wasn't supersaturated, it
maybe even close to saturation.

Near the surface, you know, relative humidity is about 50%. So somewhat
damp but not soaking.

Man: Is that everywhere or is it just because of the probe?

Ralph Lorenz: That's only an in-situ measurement made by the probe.

Man: Right. But I mean is that because the probe warmed it up?

Ralph Lorenz: Oh no, no, no. This is all in the atmosphere before the
contact with the surface.

Man: Okay.

Ralph Lorenz: Now, there was - which, I'll get on to that in a later
slide, all right?

There's an independent measurement of the methane abundance on the
surface or just near the surface from the Descent Imager and Spectral
Radiometer, it took - it has lamp to take a surface spectrum, you know,
the light from the sun is filtered through the atmosphere and so it's
relatively weak and has all these big gaps in it where methane has
absorbed the light. So we carried a lamp specifically for taking the
surface spectra.

And even from 20 meters, you can see big methane absorptions. And the
green one is the one that matches best and that indicates about 5%
methane which is in good accord with the gas chromatograph measurement.

Okay. Next slide is some of the other piles of spectral data the DISR
took. This is an upward-looking spectrometer.

And the wavelengths here runs from 500 nanometers, which is sort of
green, out through red to 700, and then into the near infrared, the far
end at about 940 nanometers. It's about the same wavelength that a TV
remote control uses. The infrared LEDs used in remotes operate at about
940 nanometers.

That's the wavelengths where most of the images of Titan surface have
been taking with Cassini's camera and where we made the first match with
HST in fact.

So, you can see, the curves are labeled by the altitude at which they
are taken. And this is an upward-looking spectrometer, so basically it's
sort of brightness and color of the sky. So you can see at 140
kilometers, we're above most of the atmosphere. And so, it's like, you
know, flying in Concorde or something. And the sky is pretty black, it's
a little bit blue but it's very dark.

And as we go descend to more and more of the atmosphere and more and
more of the haze, there's more scattering so the sky gets brighter
overall.

And you can see, it also - these absorption bands start picking up. In
particular, you can see the one at 889 nanometers and 730.

So, ultimately, these data are going to be used to measure the particle
shapes of the haze particles which may vary with altitude, particle
size. And, I guess, this may also give us actually some very good
methane absorption coefficient which will be useful in interpreting the
results from the VIMS instrument mapping Titan's spectral
characteristics - the surface - spectral characteristics of the surface
really relies on a good haze model and good compensation for the
absorption of methane.

And so, the data taken by the Huygens probe is going to be instrumental
in that sort of analysis which really hasn't started in earnest or
certainly the results haven't been forthcoming very quickly which is a
difficult problem.

The next slide is a mosaic of the descent images, downward-looking
images. You can see the "coastline." There's several dendritic patterns
on the surface.

The one sort of at 9 o'clock has a rather stubby sort of branches. And
it's a right angle branched angle which maybe related to sapping to -
basically, not ground water, but, you know, liquid methane flow on and
under the surface. It might even be that that crack which is pretty
straight is associated with some sort of fault or perhaps even
cryovolcanic activity.

The dendritic pattern which is more crisply defined towards the top of
the image is much more characteristic of rainfall and is very
reminiscent of a lot of landscapes not too far from the one I\'m in
right now.

The times at which the images were taken in seconds after the parachute
deployment command (unintelligible), (D-0) as we call it are shown. And
that 4,800 time period is - where we cross the coastline is also where
the motion sort of dumped out.

I really can\'t interpret the sort of arrowy patterns in this image.
Clearly, there are some indications of flow. It maybe that it's related
to flow of - flow by wind rather than flow of liquid. But there's a lot
of interpretation going on and the correlation is the orbital
measurement as well.

Next slide is the famous pictures from the surface.

I'd like to understand - I'd have to check with them formally that these
were actually the first images that came up on the screens of the DISR
Team because the probe lasted so long, the - I think they only had -
they were only sort of expecting a three, you know, a three-digit count
of images. And so that counts have wrapped around. And so, actually the
first images they saw were the ones that have been logged after the
probe had landed and basically counted at reset.

But we have no right to expect these images. These are an amazing bonus
for the mission. Of course the probe could have just failed at impact,
design never permitted, change is specific before surface impact
survival. I mean there was always the intent to keep communication,
thermal and power budgets open for at least three minutes on the
surface, maybe longer.

But there's no legs, no shock absorbers, no - nothing like that. So
survival of impact was a bonus but, you know, the parachute could have
draped itself on front of the camera. The camera could have been sort of
looking face down at one of these rocks and not seen the horizon or it
could just - up into sky which might have been featureless. But we
really got this great view of what looks for all the world like a beach
with a tide out. Probably it's more like a riverbed in fact.

You can see these cobbles. One of them appears to be cracked. It seems
to be the only one that's cracked in the whole scene.

And the size distribution is sort of interesting. There's a lot of -
sort of 10-centimeter, 15-centimeter cobbles which is, I believe, too
small to be called boulders officially.

And there's a lot of finer material. There's not much in a way of sort
of, you know, 2-centimeter, 3-centimeter, 4-centimeer, 5-centimer
objects. Those appear to have been washed away. So it's - most of the
size distribution and the patterns of material is either - it looks like
a bit of a scour underneath one of the rocks there.

And the rounding of the boulders - cobbles seems to re-support the idea
that this stuff was in a liquid that flowed. And the obvious candidate
is methane.

So that really underscores the fact that fluvial processes have modified
Titan's surface.

Now that was sort of a surprise because there's really not much sunlight
to drive a hydrological cycle as I mentioned. But I'll come back to that
point in a little bit.

Man: Were these pictures taken at the moment of impact or some time
later?

Ralph Lorenz: Some time later because there's dozen of them and they're
basically all the same.

Immediately prior to impact, the camera was not taking pictures, it was
taking spectra. Because they are getting the spectra of the surface
material with - it was really an important thing for the probe to do.

One lesson I think we might have learned from the probe is never ever
design a camera that doesn't look exactly straight down, it looked a
little bit out to the side. And so we never actually got that good
images of the landing site itself. But I should press on.

This next chart shows the spectrum of the surface measured by this - in
red. The black lines are two tholins - organic materials made in the
laboratory, and the blue curve is water ice.

So you can see that maybe - I think the blue curve has - is water ice
mixed with one of those tholins.

It's not a bad match but it's not a perfect match, so we still don't
really know what the surface stuff is. It's clearly dark. It has
signatures that are certainly consistent with it being an ice organic
mix. But whether you can make an exotic combination purely of organics
with no ice that matches it, it remains to be seen. That's still being
worked.

Next chart is the impact as recorded by accelerometers. The black curve
is the impact accelerometer on the Surface Science Package, ACC-I it's
called, that was dedicated for solid impact measurements.

The red curve is the HASI accelerometer which is intended for
atmospheric measurements and measurements on the surface. It had a lower
range, it wasn't sampled as fast, it wasn't optimized for the impact but
in fact it was - its results are more or less consistent.

You can see that one big negative spike there. We think that's because
the position of the HASI accelerometer at the center of the probe which
is basically in the node \-- node or antinode.

So it's - basically there's a big structure or oscillation in the probe
that causes that negative spike, but otherwise the two are pretty
consistent.

So it's sort of a fender-bender, it implies the surface material was
relatively soft, something like dry sand, wet sand would do that, wet
clay, or packed snow.

As you can see in the other plots there, the blue and the green, these
are measurements in another axis - in two other axis, the horizontal
acceleration. You can see there's a bit of a bump \-- what's that \--
20th of a second after the initial impact. Now, whether there's a little
bit of bouncing, we're not quite sure if it was, it was just a
centimeter or so.

But generally, the instruments on the probe showed signatures of motion
for a second or two but it still needs to be worked out how much of that
is probe structural response or if it's actual motion.

The next slide is the penetrometer. This is part if the Surface Science
Package sticking out to the bottom of the probe there.

The penetrometer is about the size of your finger, 14 millimeters in
diameter, titanium round-headed bolt that sandwiches a kit or electric
ceramic between two plastic washers. The ceramic generates a charge when
it's compressed, so if this thing is driven into the ground, it
generates a voltage history which corresponds to the force profile on
that kit.

And you can see in the lower right, a selection of different materials
that drop this thing into the ground. You know, my PhD research back in
England in 1994, sand is top left, this sort of characteristic ramp up,
wet clay. Top right is a - has a pretty constant resistance. It
basically behaves as a plastic material with a constant deformation.

And at the bottom, there are two kinds of gravel \-- fine gravel and big
gravel. And the size of the spikes and the spacing are related to the
particle size of the gravel.

So those were the things I was expecting see. And, you know, 12 years
later.

You now, I physically torqued the bolt on there, I chose the wires, I
stripped the wires, I held the wires in place, I needed an approved
technician who had to do the actual soldering. You have to have a space
qualification to do that.

So, ten years later, a billion miles from Earth, it worked for the 1/20
of a second. It was supposed to do its thing. And it gave us data which
looked pretty uninterpretable at first.

We have to generate some interpretations of the fly that night, I mean,
there was all these journalists wanting sudden news, you know, what did
we land on, you know, was it liquid, was it solid?

And in fact this plot was shown on live BBC TV that evening.

And what you see is, I mean, I didn't know what's making that spike at
the beginning, I thought maybe the thing had failed, that maybe there
was a breakage somewhere or there was an electrostatic discharge maybe
when we touched the ground. But it does seem in fact to be consistent
with striking either a brittle hard layer on the surface or perhaps a
pebble. We sort of went with the brittle layer thing just the last - we
came up with the crème brule analog.

And in fact, a new generation graduate students have literally done the
experimenting of crème brule. It doesn't look too bad.

We are more inclined to believe at this point that the penetrometer
struck a pebble, maybe that one that's cracked in the foreground in the
image, we can't be sure. That accounts for the spike. But generally,
it's a pretty constant resistance.

That broad hump is basically where the rest of the probe starts
contacting the ground and resisting penetration.

But the two measurements of bearing strengths, this one on the small
scale and the larger one, sort of a larger scale of measurement from the
impact accelerometers can be reconciled if basically the probe drove one
of - some of those cobbles into the ground. But the ground is basically
soft sand or something. And the deceleration is moderated a little bit
by the cobbles acting as sort of penetrometers in their own right.

You can see the data isn\'t consistent with the bottom right, which is
just plain sand without a spike or without a pebble or a crust.

So that was that. Next slide.

I made a little pilgrimage to London. I found out that, in fact, the
penetrometer was on display in the London Science Museum a few weeks
later. And in fact, the instrument that was shown there, it was labeled
as an engineering model but actually, the flight model is the one that I
built that was, you know, that seem to fit together the best with one
that, you know, we thought - we'll send this one to Titan. This is the
best of the four we made.

And we built a flight spare, in fact, a couple of flight spares.

And during the final assembly of the Service Science Package, a
technician applied torque to the wrong part and in fact broke the little
ceramic washer. So it's actually the flight spare that did this thing on
Titan. So if you have, you know, kids who are upset at being, you know,
a substitute player on a soccer team or an understudy in a play, you
know, their day may come, they may be called upon to step up, so you
should always have a flight spare.

The next slide is this business on the surface methane. You can see
after impact, the nitrogen level stayed pretty constant but the methane
in the instrument was enhanced. We believe that's because the inlet
heated volatilized material from the surface, basically sweated out some
methane.

And I've been doing some work to model the temperature history, it
wasn't measured at the tip itself, it was measured at the heater of some
distance away. But it seems to be consistent with the surface material
being physically wet or damp. It wasn't - it's not the case of
(unintelligible) being de-volatilized. There was actually a liquid
present.

And you can see the mass spectrum of the surface material is really
quite rich, there are a lot of organic materials there.

So next slide is a top view of the probe.

And the so funny picture on the right is the antenna passing the
variation in signal strengths that comes out in different angles from
the probe. And that turned out to be quite important. We have to take it
into account in the probe mission redesign when we had this receiver
problem identified.

Going on to the next slide.

You can see there's lot of variations in this signal strength determined
from the housekeeping on the Huygens receiver on Cassini. You can feel
these variations due to the spin of the probe and the motion of the
probe under the parachute. And there's a sound file on the Web that you
can play if you're interested.

And then it gets changed very distinctly at the moment of surface
impact, but still continues to change. They're slow variations but
they're quite deep and that wasn't anticipated as such but can be
explained quite nicely though, I'll show you in a moment.

Next slide shows a sort of a (heartbeat) traces of how the spin
modulation gets very periodic with repeating variation to the signal
strength. And that allowed us to reconstruct the spin rate history, and
in fact, the direction.

And going on to the next slide, you'll see that in fact that direction
of the spin was not that anticipated. It started out the right way but
the probe spun down, and then spun up the wrong way. And we really don't
understand why that should.

The vanes were on the right way as far as we can tell. There was a
terrestrial airdrop test balloon as I mentioned that also exhibited
apparently this anomalous rotation. But why isn\'t understood, we need
to go back and understand which features were common to the test and
flight and which things may be different, whether it's just coincidence
they both went the wrong way. Maybe we need to do some wind tunnels
test, that's going to take a while to we explain.

It might be some funny interaction between the probe and the parachute.
We really don't understand this one.

Anyway, as - after Huygens landed on the ground, Cassini set, and was
listening to it and received the data.

But if you just map the track of Cassini through the sky, through that
antenna pattern, you can get one of those blue curves in the upper right
without all those big variations.

So there's another effect at play.

Interestingly, we also got the signal a little bit after Cassini set
below the optical horizon. The - you may know, that the radio horizon is
actually a little bit further away or below the optical horizon because
the radio beam gets diffracted by the spherical body of the planet, and
refracted in fact, by the atmosphere slightly. But that doesn't explain
this deep scalloping pattern you see in the radio strength history.

Next slide shows the explanation. It basically what engineers call
multipathing, you know, why if you have a TV set with a rabbit-ear
antenna, not a cable or a satellite dish, how you can get good reception
and then somebody stand in just the wrong place in the room and then
suddenly the reception goes to hell. Or if you move the antenna very
slightly you get very dramatic change in picture quality, or cell phones
are notorious for this as well.

Basically, there's interference in a constructed and destructed sense
between direct and reflected rays, and that's what happened on the
probe. There's enough radio energy leaking out downwards from the
antennas to make a signal that interfered with the direct signal, and
that effect is particularly profound at low elevations. And you can make
a model.

The next slide shows some of the plots here to fit that history, and it
seems to fit very well. And it's a very, very sensitive measure of
exactly how high above the ground the antenna was. And that basically
tells us that the probe was sitting on the surface. It didn't penetrate
very deeply, again, consistent with this idea that we drove a couple of
those cobbles into the ground.

It also indicates that the surface roughness is typically a few
centimeters, going on to the next slide, in the direction that the radio
signal went. So that's the direction that isn't the same as the
direction viewed by the camera which is shown in blue there. So we
have - I mean it's not earth-shattering but it is an independent measure
of the surface properties that we couldn't otherwise get - just from the
signal strengths.

Now this interference effect, you can actually demonstrate with very
unique expensive electronic parts. You get this little ultrasound
receivers used in range finders on robots and electronic tape measures.
And you can - just by putting those a few centimeters off the ground and
driving them with a 555 oscillator and receiving them with a little
amplifier chip, you can reproduce these kinds of patterns.

And there's a little video where you can see very unclearly, it's a bit
dark. I\'m moving the receiver up and down and there's a light bulb
whose intensity relates to the intensity of the received signal, just
like Huygens data (unintelligible). Move it up and down, the signal
strengths vary because of this interference pattern.

So that will be published, the circuit details, if anyone wants to
reproduce it, will be reproduced in Servo Magazine which is an amateur
robotics magazine, in the May issue. So it'd be, I guess, a couple of
months. But it's kind of a fun thing to try. It might be good in the
classroom.

Okay, next slide. Another little engineering investigation I did. We
better wrap up soon.

You can see this is a probe at Kennedy Space Center; Cassini is in the
background there. And you can see this big hose pipe basically blowing
cold air into the probe. Actually the cold air got turned up too high
and it shredded some of the insulation on the probe which is why we had
to have a couple weeks launch delay actually to clean that up. But you
need the cold air to remove the heat from the electrical power
dissipated in the interior. And if you do to a test on Earth for any
length of time, the probe will start warming up because it's got all
this insulation to keep it warm in Titan's cold environment. So you need
this kind of hose pipe but it just underscores how much heat is produced
on the inside of the probe.

The next slide shows so schematic (internal dissipation) and the layer
of insulation. And that's removed by forced convection as the probe
descends through the cold air. You get a wind-chill, basically. And the
probe is dissipation a couple of hundred watts of heat from, you know,
the radio transmitters and the experiments and all the computers and so
on. But the probe cooled down, so in fact it - the probe was losing more
than 250 watts of heat.

Then on the surface, it's still generating heat but there's much less
force convection because the probe isn't flying through the air anymore.
There's only a little bit of free convection from the buoyant rise of
warm air, and whatever wind was present.

So going on to the next slide, you can see, just - this is one of the
temperatures - one of the batteries. Again, rather crude engineering
data but it gives an interesting insight into the surface environment.

You can see the probe cools down a couple of Kelvin every thousand
seconds. And then on the surface, that cooling rate is much, much lower.
So basically the convection is much lower.

And if you look at the next slide, you have to build a little model with
a couple of thermal resistances to account for the insulation and so on.
But if you compare the heat loss of 600 watts also during descent with
the 350 watts net loss on the surface, you basically can constrain the
wind. The wind can't have been much more than about a fifth of a meter
per second on the surface for the hour so, the probe is on there.
Otherwise, the probe would have cooled more quickly than it did. So it's
kind of an independent measurement of wind speed just from the
wind-chill.

Okay. The next thing is the location of the probe landing site.

You can see here a mosaic made by amateurs. You may remember the probe
data was released - the pictures rather were released very early on. And
a lot of amateurs made a very nice mosaic and even dealt with some of
the flat fielding issues.

And you can see in this side-looking mosaic, we showed this quite well.
There are a couple of black lines on the frames \-- they were 470, 461
and 440. And those turned out to be key in identifying the landing site
in radar.

The next three slides I just set put together by Jonathan Lunine. This
is part of the T8 radar swath as the background. And the bit that fades
in and out and you page through backwards and forwards is the mosaic of
DISR images.

And you can see that these two dark streaks kind of match up very well.
And that's what nailed the landing site.

You can see that in a lot of other parts of the image the coloration is
not particularly good. The radar instrument is seeing different aspects
of the surface than the camera. The camera is responding to optical
brightness and topography only to a limited extent, whereas the radar is
much more susceptible to surface roughness and slope effect. But those
two streaks really nailed the landing site.

And we believe those streaks are sand dunes, and that's stuff that will
be published in Science in a few weeks. We actually find a lot of sand
dunes elsewhere on the T8 swath in particular.

We've seen these dark streaks in T3 in February last year but we didn't
really know what to make of them. But the ones we saw on T8 were much
easier to understand.

But anyway, with this correlation, we end up with the Red Cross as the
location and the lat/longs that are indicated there, to within a few
kilometers now. We expect the VLBI experiment to be consistent with
that. It may be the VLBI experiment actually gives us a better timing
ephemeris than we have had.

But in fact, the location determined from this correlation was only a
few kilometers away from that; that we judged from the navigation of the
probe's delivery and from the Doppler shift information.

So that'll work quite well.

And in fact, the correlation of the DISR data with VIMS and ISS data
from the orbiter is enabling the DISR location in the radar swath, and
the radar swath is very well-navigated because range is very precisely
measured with radar of course. That basically ties down the whole
mapping effort to one specific location on Titan, that's really sort of
nailed the (unintelligible) control points.

So I better wrap up.

The next slide is from TA radar image where we've seen in October of
'04, before the probe, a couple of little bright sinews channels and the
sort of striations that look maybe like alluvial fans. We couldn't be
sure that's what they were. We're still not sure that's what they were
to be honest.

But then the paradigm of Titan is it's a place modified by rainfall and
by rivers which was not at all established.

But then, next slide shows the DISR image, I mean, that made it
abundantly clear, it's like, "Wow, oh, obvious." It was \-- there are
rivers and rain.

So next slide shows another thing we saw on T3. And now, knowing from
the probe that it's not absurd to suggest that Titan is modified by rain
and rivers, it's pretty easy to interpret this as exactly that.

This braiding, you see a lot of branching and re-converging and so on,
is very characteristic of energetic flows like the ones you get from
under ice sheets when there's a volcano under the ice sheet, the
(unintelligible) in Iceland, those characteristics of the desert
Southwest. Basically, you get relatively little rain fall on average,
but when it does happen, it happens in big storms so it's very energetic
event. So even so, the average rainfall in the desert is low, the
landscape is dominated by fluvial features like canyons and washes, and
that may be what's happening on Titan basically the - because the
atmosphere can store so much moisture, I mean, it basically a
millennium's worth compared with about a month's worth for the Earth.

It may rain very infrequently but when it does, it does so in such ways
to make these very fluvial channels.

I was struck \-- next slide \-- just looking at the window when I flew
into L.A. once that you get this very characteristics sort of braiding
pattern on a slightly different scale; this is about maybe 20 kilometers
on the side whereas the radar image more or like 200. But the pattern is
very similar, that's some - so it seemed that's really developing on
Titan that even so the working fluids processes or the rates that which
processes occur are very different. The processes themselves and the net
result, the land forms that are produced are very similar to those on
Earth, more - very much the, the most earth-like place in the solar
system.

So, the slide - last but one.

Just to sum up, you know, Huygens was international project. I mean
that's why someone with a British accent who worked in the Netherlands
and Britain and is now teaching in Arizona is talking to you. There\'s
an awful lot of data from the probe that will yield insights in many
years to come. There\'s a lot of collaborations between probe and
orbiter that may been - that haven't been done yet.

We're basically tying up loose ends in the sense of understanding what
actually happened during the probe mission, but some of that may take a
while because it may need wind tunnel test and things like that. But it
really - really the Huygens mission has been, I mean, you know,
wonderful privilege to be involved in. Frankly, I could have landed on
my feet in a better place at a better time. It's really been a lot of
fun.

And I think it sets the stage that Titan is a place we want to go back
to and see more of. And maybe one of the leading ideas is a balloon or
an airship.

So with that, I'll close, it's a little short of the (SSP) team in
Darmstadt with the probe in the foreground. And it's been a lot of fun
and I\'ve enjoyed talking to you, and I guess I'll take any questions we
can squeeze in in the time left.

Man: Hey, question?

Trina Ray: Go ahead.

Man: Way in the future when somebody is walking around on the surface of
Titan and they stumble across this thing, what the - I mean is it going
to have like being crusted do you suppose, with this precipitation or
whatever the falls from the sky?

Ralph Lorenz: That's an excellent question.

In the old days I would have said yes. It's not - we're really getting a
picture of Titan as, it's not place you can talk about. You can't say
Titan is like this. You can say this part of Titan is like this in this
season. And while you, you know, the atmosphere looks - the haze looks
uniform sort of everywhere, it's clearly not. There is an enhanced haze
feature over the winter pole specifically.

And so, it maybe that much off the haze gets precipitated down to the
surface at high latitudes. I mean, clearly the probe landing site at low
latitude has a lot of dark material. But whether that was actually
deposited from the air or whether it was washed thereby by rivers is
another story.

You can see that the cobbles look brighter than the stuff they are
sitting on, you know, the sand is sort of dark, you know, the sand
really is, it seemed that way.

So why are they dark? So why are they not dark too? Is it because
they've been washed clean over a timescale short with the haze
deposition or the haze deposition just not happened?

It might be that the probe, you know, it's sufficiently long in the
future that we visit the probe it won't be there anymore that it would
have been washed somewhere by...

Man: Oh, what a neat thought.

Ralph Lorenz: ...these flash floods.

Man: Yeah, very good. Well, I appreciate it. Thank you.

Ralph Lorenz: Sure.

Trina Ray: Any other questions?

Well I know, Ralph, I\'ve been spending a lot of fun time just - on
those three slides that you have with the radar and the DISR.

Ralph Lorenz: Uh-huh.

Trina Ray: That is just enormously fun to go back and forth on those and
just say, "There are so few features that are the same."

Ralph Lorenz: It - I mean, we sat and stared at JPL. I mean it was - we
sort of joked about it being the breakfast club. It was a Saturday when
the radar image became available. So we spent a whole Saturday in the
radar boiler room to \-- (Steve Wors) (unintelligible) where we have a
big wall we can project big images on.

And we just look around, we couldn't find anything that matched up. It
was just kind of crazy.

And so we had to sort of think about it for a while. And somebody
pointed out the two cat scratches. Now the DISR Team was reluctant to
draw too much conclusively from the side-looking images because those
are, you know, looking through a long path-length through the
atmosphere. And especially anything that's just plain horizontal could
easily be a sort of flat fielding effect.

Now the amateurs, you know, don't have to worry about that sort of thing
so much. They don't have to go through peer review. They just gleefully
pasted all these images together.

So it was one, I guess, one of the amateur products that kind of just
caught our attention and allowed those two streaks to match up. And
then, armed with that information, the DISR guys \-- (Beshar) and (Lisa)
and others who are working with, you know, re-projected the raw data
after they had been cleaned up and made a nice mosaic that you can do
the matching with.

But, yeah, it really was those two streaks that were the key.

Trina Ray: Yeah. You haven't those, I don't know what you ought have
done.

Ralph Lorenz: Yes.

Trina Ray: I guess you would have said, "Well, this is our best guess,"
I guess.

Ralph Lorenz: It would've been, yeah, it would have been quite
disappointing.

Man: Ralph, this - can you hear me?

Ralph Lorenz: Yeah.

Trina Ray: Yeah.

Man: I have a question for you.

Is anybody doing any modeling to suggest whether the season on Titan
might have - might trigger these possible monsoons?

Ralph Lorenz: Excellent question. I refer you to the paper by (Pascal
Ranoe) published in Science on the 13th of January of this year. It got
a global circulation model that now incorporates fairly good handling of
the methane cycle. And what it seems - what his model shows is that
during polar summer, you get quite strong precipitation at high
latitudes, and we\'ve seen those clouds with Cassini and with Keck from
the ground.

There are sporadic storms or, you know, cloud events \-- let's call them
\-- at all latitudes I think all the time. But there\'s also a steady
characteristic mid-latitude pattern, at around 40 degrees latitude which
we\'ve been seeing a bit with Cassini as the season changes from polar
summer.

But that's a particularly nice observation because - and this is paper
that's just been taking too long to get finished. We actually started on
it in 1996.

We actually observed with the Hubble Space Telescope a cloud at 40
degrees north back in 1995, and that's fully consistent with this model.
So, you know, the model didn't - it wasn't adjusted to reproduce that
observation, it just happens to be what I know about.

So yes, we are starting to get an impression of when, and where, and how
often this sort of events may occur. We shouldn't say we know exactly
how often it will be that a given spot encounters rainfall, just whether
there will be rainfall somewhere on Titan.

Now, the models that have been made of individual thunderstorms, not
this sort of large scale seasonal climate model but meter scale model of
an individual storm, you find they can dump maybe 10 centimeters of rain
in just a few hours, you know, quite consistent terrestrial tropical
thunder showers. So, easily enough liquid to carve these river valleys.

And one of the bizarre things is that because Titan's atmosphere is so
vertically extended and the gravity is low and the atmosphere is thick,
raindrops fall fairly slowly. In fact, modeling Titan raindrop is
something I did in grad-school actually stimulated to work on the
possibility that Huygens probe might ice up. There are areas in the
Titan's atmosphere where the methane should be in solid form and so it
might ice up. But turned out not to be a problem.

But I looked at methane raindrops and they fall like big snowflakes do
on Earth, about a meter and a half per second. But these big clouds on
Titan would form and evolve in a matter of three hours or so, and they
could dump all this rain, and then the cloud disappears. But it's still
another hour or so before the raindrops hit the ground.

So, you might not even, you know, know that the storm is coming. You see
it coming, you think it's all over and then an hour later, suddenly
this, you know, 10s of centimeters of liquid starts raining down. It's
really quite bizarre.

Trina Ray: And has Cassini confirmed any ponds of lakes of methane?

Ralph Lorenz: Confirmed is a tough sort of word. It's turning out to be
really rather challenging even when you actually just start thinking
about it. How are you sure that something is a lake or pond?

There are certainly pond-shaped or lake-shaped features that are
optically dark. There are also vaguely - some vaguely pond-shape radar
dark features. But knowing whether they are not just, you know,
pond-shaped patches of soot versus, you know, black liquid is actually
rather challenging. One discriminate would be a seeing a specular glint,
sort of mirror-like reflection of the sun on such surfaces. And those
haven't having been seen yet.

Now, the same model I\'ve mentioned by (Pascal Ranoe) indicates that the
low latitude on Titan should dry out. Over time the methane should be
evicted away and it will accumulate at high latitudes. So the high
latitude should be humid, and so, probably wet.

Now the best candidate perhaps for a hydrocarbon lake is this dark
swimming pool-shaped thing - about the size of the Lake Michigan I
guess, near the South Pole, the Imaging Science System saw. And that's
consistent with, you know, liquids maybe accumulating at the pole.

I would really rather give a definitive answer to the question after the
end of July this year when we have T16 which will give us a radar swath
more or less over the North Pole.

There was a very tantalizing shoreline-looking feature seen on T7. And
after the shoreline the radar image kind of gets black and relatively
featureless. So consistent with, maybe a liquid but not conclusive.

So the conclusive data is a very hard one to address. But I think
there'll there and they will turn out to be in high latitudes.

Man: Thank you.

Trina Ray: Are there any other question?

Man: Yes. Ralph, who made the battery that lasted (unintelligible)
period?

Ralph Lorenz: Who made them?

Man: Yeah.

Ralph Lorenz: I think there was - they\'re lithium-thionyl chloride
batteries, in fact, the same one is used on Galileo. I would have to
look it up. I have to look it up.

Man: Okay, thanks.

Ralph Lorenz: I might be able to look at it up very quickly actually.

Maybe you can throw another question at me while I\'m trying to find
out.

Trina Ray: Well, if there are no more questions I can also give a
shameless plug for the next telecon.

We'll be having Julie Webster who is the Spacecraft Manager for Cassini.
She'll be giving us a detailed look at the Cassini spacecraft, all the
basic subsystems on the spacecraft, and it will be wonderful reference
for any future talks that are given that she won't discuss any of the
science instruments other how they relate to the basic power and
commanding subsystems. And I expect that one - even though it's only one
speaker, I expect to go probably the full two hours on that next time
only because she has so many topics that are of interest.

And then after that in April, we have coming up, Dr. (Josh Caldwell)
will be giving a talk on UVIS occultations. And the special request,
somebody on the telecon mentioned last time, we - many of you had
requested a tutorial, sort of a tutorial, three-dimensional ring
structure \-- the ring structures in the wave, the bending waves, the
density waves that sort of thing. So in addition to talking about the
UVIS Occs, he's also going to have a little separate ring tutorial that
will also be an excellent reference for the future.

Ralph Lorenz: Okay, I've looked up the batteries. It's - they were
actually made by Alliance in the USA.

Man: Thanks.

Trina Ray: Perfect timing.

Do we have any other questions?

Man: What can you say about the height of the surrounding terrain?

Ralph Lorenz: The - well you can see the cobbles boulders are consistent
with the - in the image are consistent with the regular measurements of,
you know, just a few centimeters. Now, there might be few meters, no
more than that of topography on the horizon.

The radar altimeter results have been a bit slow in forthcoming. It
turned out over the years, with these long projects, you have to sort of
factor in career evolution, the relatively junior guy who have the
responsibility for the science with the radar altimeter back in 1992 is
now the project scientist for Venus Express. So he's been pretty tied up
for the last year.

But, there\'s maybe 20 meters of topography across that dark plane. The
brighter terrain, on which you see the river networks, is about 100
meters high up.

There are some stereo topography reconstructed from the images in the
DISR "Nature" paper, and that shows how deep some of those gullies are.
They are very steep actually, very steep-sided. But that's the
background there.

In general, judging from the orbiter radar, Titan is somewhat flat. I
mean there are mountains, I mean, there are isolated hills and chains of
hills maybe a few hundred meters high. But overall, it's really quite
flat.

Man: Thank you.

Trina Ray: So Ralph, maybe the final question, it took an awful lot of
time and energy and work, especially time, many tens of years to get up
to Titan the first time. How long do you think it will be before we
would visit it again?

Ralph Lorenz: I\'m thankfully young enough that I can afford to be a
little bit sanguine about this. I expect it in my career. I hope that it
happens in career.

I\'m thinking probably Titan arrival in the 2020s. I think,
realistically, our project might get defined kickoff towards the end of
the Cassini mission, so 20, you know, 2009 and 2010, that sort of
timeframe.

It will take six or seven years to get to Titan unless we do something
very exotic, so allowing for a bit of development there. I think unless
the outer planet's program is dramatically skewed in some way, I think
the 2020, hopefully, the early 2020s.

Right now, there\'s still a bit of an emphasis on Europa for the outer
solar system. And if a Europa mission is constructed it would - the
counter thinking is it would go first before Titan.

But Titan is actually easier to do in a lot of ways. It doesn't have the
space radiation problem. And even so, Titan is twice as far from the
Earth, it's not nearly as deep in the Jovian gravity well. It's not
nearly as deep in the Saturn gravity well. It's well placed in Jupiter,
so purposively it's easier to get to. And you got this big thick
atmosphere to break with when you get there.

So I think the community will slow to come around in the next couple of
years. Europa is sort of a one-trick pony. If we're into ice tectonics,
then it's great. It will be a wonderful place to do surface chemistry on
but I think that's still some way off. What can be done with the orbiter
is rather less exciting.

Whereas, Titan has all these other processes going on, as well as the
rich organic environment. So I think it appeals to a broader range of
the scientific community. And it's more technically interesting. You
know flying a balloon on Titan is much more exotic but tractable set of
challenges than building a Europa orbiter.

So I\'m confident we'll see something - something start happening in the
next decade and until it arrive in the early 2020s.

Trina Ray: Okay, sounds good.

Unless there are any more questions?

Ralph Lorenz: Did I really talk for two hours?

Trina Ray: You did, but it was absolutely fascinating. I was a little
worried when you are on Slide 13 at the first hour but you managed.

Thanks very much, Ralph. We really appreciate you taking the time today.

Ralph Lorenz: Okay, my pleasure. Have a good day.

Woman: Bye-bye

Trina Ray: Bye everybody.

Woman: Bye.

Woman: Bye.

Man: Bye. Thank you. Very good.

END