# Presentation: 861076

## The Role of Transiting Planets

Dave Latham (CfA)
30 May 2008

**The Role of Transiting Planets**
**Dave Latham (CfA)**
**30 May 2008**

## The Role of Transiting Planets

- IAU Symposium 253 “Transiting Planets”
- (Last week in Cambridge)
- TRANSITING PLANETS ARE NOW!
- A deluge of new observations and ideas

## Super-Earths

- Mass range:
- 1 - 10 Earth mass

- (GJ 436b: Gillon et al. 2007)

- Hot Jupiters

**Mass**

**Radius**

- Mass vs. Radius

## The Near Future

- Radial velocity surveys of FGK stars
- Velocity precision pushing below 1 m/s
- Reaching (minimum) masses of a few Mearths
- HARPS is reaching a rich population of hot Neptunes and hot Super Earths (Lovis et al):
- 30% frequency, 5 to 30 Mearth, P < 50 days
- Kepler  (and CoRoT)
- Kepler on schedule for 16 Feb 2009 launch

## Slide 5

## Kepler MISSION CONCEPT

- <date/time>

***Kepler M******ISSION***** C****ONCEPT**

*Kepler Mission* is optimized for finding
- 	Earth-like planets ( 10 to 0.5 M )
- 	in the HZ (out to 1 AU ) of solar-like stars
- Monitor 100,000 main-sequence stars
- Use a one-meter Schmidt telescope:
- 	FOV >100 deg2 with an array of 42 CCD
- Photometric precision:  < 20 ppm in 6.5 hours for V = 12 solar-like star
- 	=> 4 detection for Earth-size transit
- Mission: Earth-trailing orbit for continuous viewing, _>_  3.5 year duration, launch Feb 09

**Notes:**
Going on to Page 14 then, the question is how, do we do it with the Kepler Mission?  Well, I’ve already said we’ve optimized it to look for Earth-like planets in one-year orbits.  And the way we do it is we look at 100,000 stars continuously and simultaneously.  We measure the brightness of 100,000 stars every half hour simultaneously.
	We take that data with our telescope and we look at the same set of stars for the entire four-year mission.  You can't look in one place, you know, one day in another place in another day because if you blink, you’ll miss a transit.  So you have to look in the same place in the sky.
	And the way we do this is with a Schmidt telescope.  As astronomers, you’ve probably heard of Schmidt telescopes.  They’re - they have a special property of being able to look at a wide field of view in the sky, wide for telescopes that is.
	Our field of view is over 100 square degrees.  And to put that in context, think of the field of view of the Hubble Space Telescope.  If you took a grain of sand between your fingers and how held it arm’s length, that’s how much of the sky the Hubble Space Telescope can view at any one time.  It’s not a whole lot.
	But Kepler, if you take your open hand at arm’s length and hold it up, that’s how much of the sky Kepler views at any one time.  In fact, the gaps between our CCD modules, as you can see in the little diagram on the right there, those gaps are so big that you can put the full moon in between the CCD modules and not touch two modules.  So it’s a fairly - a really large piece of sky.
	The next thing is the photometric precision of the telescope, of the photometer, of the CCDs has got to be good enough to see that tiny transit.  And we’re designing this instrument - this photometer to have a noise level of less than 20 parts per million.
	Now, the reason for that is -- you go back to few slides -and you saw the size of the Earth relative to the Sun is one part of 10,000.  That’s - actually, it’s a little bit smaller than that even.
	Now, one part in 10,000 is 100 parts per million.  The change of brightness due to the Earth is actually 84 parts per million.  So, having the noise at 20 parts per million means that we will have a 4 sigma detection.  That is, the signal is four times the noise for the transit.  And then, of course, we add transits together and that improves our signal-to-noise.
	The mission itself is launched on a Delta II rockets into what we call a heliocentric orbit so that it’s not orbiting the Earth anymore.  It actually leaves Earth and goes into orbit around the Sun and basically is trailing behind the Earth as the Earth goes around the Sun.  So, it’s a slightly different orbit than the Earth.  But that way, we don’t have a problem with the telescope being blocked by the Earth at some point in its orbit as it goes around the Sun as it goes around the Earth because we’re looking at one place in the sky always.  And being in Earth orbit, that would - you can't do that.  You would end up with the Earth blocking part of the sky on every orbit.

(John Gallagher):	...you gave the Hubble a grain of sand at arm’s length.  What was the comparison with the Kepler here that...
David Koch:	Yeah.  The comparison there is an open hand.  If you just ...hold your open hand at arm’s length, that covers about 100 square degrees in the sky.
David Koch:	Another comparison I use is that the dipper on the Big Dipper is about 50 square degrees.  So, it’s like double scoop.  It’s two dips from the Big Dipper.
	...So it’s about how much of the sky we look at.

## The Legacy of Kepler

- Frequency/characteristics of planets
- Mass, radius, density, orbital distributions
- Limited by ground-based follow-up velocities
- Reaches down to Earth-sized planets
- Reaches out to Earth-sized orbits
- Host star characteristics
- Information for the design of future missions

## Beyond Kepler

- The sweet spot for Kepler is ~ 12th mag
- Photometric performance ~ 20 ppm
- Enough good targets to yield several transiting Earths
- But too faint for JWST spectroscopy
- Covers only 1/400 of sky
- CoRoT planets are even fainter
- Smaller telescope, smaller area on sky is covered
- Need an all-sky survey for nearest & brightest!

## Transiting Exoplanet Survey Satellite

- All-sky survey for transiting planets
- 2.5-million selected targets  4 < I < 13.5 mag
- Emphasis on small stars including M dwarfs
- Reaches Super Earth and even Earth-sized planets
- Predicted yield of ~1600 planets
- The Legacy of TESS
- All the brightest and nearest transiting planets
- Best targets for follow-up studies by JWST and other future missions for years to come