Newsgroup: it.scienza.astronomia
Titolo: [Fwd: [ASTRO] Sky & Telescope's News Bulletin - Mar 19, from [Stuart Goldman<sgoldman@skypub.com>]]

]
Date: Fri, 19 Mar 1999 18:56:46 -0600
From: 
ryb...@idcnet.com
 (Paul M. Rybski)
Reply-To: 
ryb...@idcnet.com
 (Paul M. Rybski)
To: 
as...@lists.mindspring.com
, 
ast...@uwwvax.uww.edu
SKY & TELESCOPE'S NEWS BULLETIN
MARCH 19, 1999
MORE MARTIAN MICROBES?
On Thursday, March 18th, NASA scientists offered new evidence that
fossilized microbes could be present in at least three meteorites from
Mars. Kathie L. Thomas-Keprta (NASA/Johnson) showed that the controversial
stone known as Allan Hills 84001 contains many microscopic crystals of the
iron-rich mineral magnetite. One-fourth of these are perfectly shaped,
same-sized hexagonal prisms free of chemical impurities. Certain bacteria
routinely produce such ultrapure magnetite crystals as a means of orienting
themselves to Earth's magnetic field, and they cannot be formed by any
known inorganic process. Of all the hints of microbial fossils seen in ALH
84001, Thomas-Keprta says the magnetite grains provide the strongest
evidence.
David S. McKay (NASA/Johnson) raised the possibility that two other Martian
meteorites, Nakhla and Shergotty, contain fossilized microbes. His
scanning-electron-microscope views show a variety of round and oval forms
found in tiny cracks within a Nakhla stone. "Are they microfossils?" McKay
asked aloud. "We don't know." But he noted that the blobs are enriched in
iron oxides, a common occurrence when a microbe dies and its cell becomes
mineralized. Moreover, the suspect features are a few tenths of a micron
across, comparable in size to many bacteria. (Many of the putative fossils
in ALH 84001 were much smaller -- too tiny, microbiologists argue, to have
been viable lifeforms.) The NASA team will attempt to examine the blobs'
interiors for hints of cellular structure and to determine whether they
resulted from terrestrial contamination. Unlike ALH 84001, which sat on the
ice fields of Antarctica 16,000 years before its discovery, many pieces of
Nakhla were recovered almost immediately after falling in Egypt on June 28,
1911. McKay's sample came from a fragment with an intact "fusion crust"
that was opened in sterile, clean-room conditions last year.
McKay also showed suspicious features from the interior of Shergotty,
though the study of those is just getting under way. Shergotty crystallized
from molten rock a mere 165 million years ago, whereas Nakhla is about 1.3
billion years old and ALH 84001 is 4 billion years old. Thus, if microbial
fossils really exist in all three of these meteorites, it means that life
has existed on Mars throughout much of the planet's history and could be
there today. NASA hopes to obtain samples of the red planet via spacecraft
as early as 2008, and the agency is currently wrestling with how best to
isolate and study the Martian material once it reaches Earth.
Thomas-Keprta and McKay reported their results at the 30th annual Lunar and
Planetary Science Conference in Houston, Texas, which this year drew nearly
1,100 researchers -- a record attendance -- from around the world.
WHENCE CAME THE MOON?
Other results presented at the conference include evidence that the Moon
did indeed form from the remnants of a collision between the Earth and a
Mars-size body early in the history of the solar system. New support for
this scenario comes from data collected by NASA's Lunar Prospector
spacecraft. Analysis by Alex Konopliv (Jet Propulsion Laboratory) of
gravity measurements reveal that the Moon has a small metal-rich core,
amounting to only 4 percent of the body's total mass (Earth's core is 30
percent of the planet). If the Earth and Moon had coalesced from the gas
and dust of the solar nebula at the same time, they should have similar
compositions and core sizes. However, a large object's grazing collision
with the proto-Earth would have blasted some of the iron-poor outer layers
into space. Much of it would have remained in Earth orbit and then amassed
into our satellite.
HUBBLE EXAMINES GALAXIES IN INFRARED
Pictures released Thursday by the Space Telescope Science Institute reveal
where stars are being born in spiral galaxies. The images are part of a
survey of about 100 spirals. The dust-penetrating gaze of Hubble's Near
Infrared Camera and Multi-Object Spectrometer (NICMOS) highlighted knots of
glowing hydrogen in the galaxies' arms, where the stellar raw material is
being irradiated by ultraviolet light from massive newborn stars. The
reddish knots seen in the cores of some galaxies (such as NGC  2903) could
be from star birth or from the radiation generated by an active nucleus,
perhaps powered by a massive black hole.
DAYTIME ALDEBARAN OCCULTATION
The Moon occults (covers) Aldebaran during daytime for eastern and central
North America on March 22nd. If the sky is clear, you should be able to
watch this event with a telescope. See the timetable in the January Sky &
Telescope, page 115, or at
http://www.skypub.com/sights/occultations/lunar/lunarchart.html
 (the times
and dates in the table are in Universal Time).
EQUINOX UPON US
The Sun arrives at the March equinox at 8:46 p.m. EST on Saturday, March
20th, crossing the equator heading north. This is the moment when spring
begins in the Northern Hemisphere and fall begins in the Southern
Hemisphere.
THIS WEEK'S "SKY AT A GLANCE"
  Some daily events in the changing sky, from the editors of SKY &
TELESCOPE.
MARCH 21 -- SUNDAY
  * The crescent Moon shines high in the west this evening, far to the
upper left of Venus and Saturn. Higher to the Moon's upper left is orange
Aldebaran. To the Moon's right or upper right are the Pleiades.
MARCH 22 -- MONDAY
  * The Moon occults (covers) Aldebaran during daytime for eastern and
central North America. If the sky is clear, you should be able to watch
this event with a telescope. See the timetable in the January Sky &
Telescope, page 115, or at
http://www.skypub.com/sights/occultations/lunar/lunarchart.html
 (the times
and dates in the table are in Universal Time).
  * Early Tuesday morning the faint asteroid 120 Lachesis will occult a
10th-magnitude star in Libra for up to 39 seconds for observers along a
wide path from central Canada to the Southwest. The occultation should
happen within a few minutes of 7:57 Universal Time March 23rd in Winnipeg
and 8:04 UT in Arizona. See the finder chart in the March Sky & Telescope,
page 106, or in the occultation section of Sky & Telescope's Web site,
http://www.skypub.com/sights/occultations/occultations.html#menu
 (where
late news and prediction updates may also be posted).
MARCH 23 -- TUESDAY
  * The Moon shines high to the upper right of Orion in tonight's evening
sky.
MARCH 24 -- WEDNESDAY
  * First-quarter Moon (exact at 5:18 a.m. Eastern Standard Time).
MARCH 25 -- THURSDAY
  * The red long-period variable star R Leporis, "Hind's Crimson Star"
below Orion, should be at maximum brightness (7th magnitude) around this
date.
MARCH 26 -- FRIDAY
  * Saturn's largest moon, Titan, can be found four ring-lengths to
Saturn's west this evening through Sunday evening. A small telescope will
show it.
MARCH 27 -- SATURDAY
  * Regulus is lower left of the Moon early this evening, and directly left
of it later in the evening.
 ============================
  THIS WEEK'S PLANET ROUNDUP
 ============================
MERCURY is hidden low in the glow of sunrise.
VENUS is the bright "Evening Star" in the west during and after dusk. Much
fainter Saturn appears to its lower left early in the week, and farther
below it later in the week.
MARS rises around 9 or 9:30 p.m.  It's well up in the southeast by
midnight, shining brightly in western Libra at magnitude -0.8. In a
telescope Mars is 13 arcseconds in apparent diameter. It will reach
opposition on April 24th and pass closest to Earth on May 1st, when it will
appear 16.2 arcseconds wide.
JUPITER is hidden low in the glow of sunset.
SATURN shines to the lower left of bright Venus early this week, and
farther below it later in the week.
URANUS and NEPTUNE are just emerging from the glare of sunrise.
PLUTO, magnitude 13.8, is in Ophiuchus in the south before dawn. See the
finder chart in the March Sky & Telescope, page 103.
(All descriptions that relate to the horizon or zenith are written for the
world's midnorthern latitudes. Descriptions that also depend on longitude
are for North America.  Eastern Standard Time, EST, equals Universal Time
minus 5 hours.)
More details, sky maps, and news of other celestial events appear each
month in SKY & TELESCOPE, the essential magazine of astronomy. See our
enormous Web site at 
www.skypub.com
. Clear skies!
SKY & TELESCOPE, P.O. Box 9111, Belmont, MA 02478  *  
617-864-7360
 (voice)
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