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SKY & TELESCOPE'S NEWS BULLETIN - FEBRUARY 16, 2001
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NEAR AND EROS MEET
Although given no better than a 1-in-100 chance of survival, the Near
Earth Asteroid Rendezvous (NEAR) spacecraft thumped onto the dusty,
boulder-strewn surface of minor planet 433 Eros on Monday and lived to
tell about it. The spacecraft continued to broadcast to Earth after
touching down at an estimated 1.5 meters per second at 3:05 p.m. EST
(20:05 Universal Time). As mission personnel looked on anxiously, NASA
tracking stations in California and Spain continued to receive a
low-power signal (but no data) after the first-ever landing on a small
solar-system body.
The landing sequence began about 4 hours earlier, as a rocket firing
forced NEAR-Shoemaker out of its 35-kilometer-high orbit and sent it
on a collision course with Eros. Four more rocket firings, beginning
at altitude of 5 km, slowed the craft during its 47-minute freefall.
Engineering data and altitude measurements showed that the spacecraft
descended to the surface just as planned, perhaps bouncing once before
settling down tipped to one side and resting on the corners of two
solar-cell panels. The touchdown site is on the shoulder of Himeros, a
broad depression in the southern hemisphere.
NEAR Shoemaker's onboard camera radioed more than 50 pictures as the
surface drew closer. The landscape looked smooth and dust-covered for
the most part, peppered with myriad boulders ranging from house- to
fist-size. But mission scientists were most surprised by the lack of
small impacts. "We are absolutely amazed by the absence of small,
fresh craters," exclaimed imaging-team leader Joseph Veverka, as well
as by numerous shallow sinkhole-like depressions. The final frame,
taken from a height of 125 m, showed an area 6 m wide and revealed
details only about 1 centimeter across. NASA had intended to cease
tracking the spacecraft on February 14th, when the mission was to
officially end. However, since the spacecraft survived, it has been
granted a reprieve as scientists try to glean more useful data from
the probe.
LIFE UNDER FROZEN MARTIAN LAKES?
The Antarctic lake Vostok, has received much attention for being an
analog to the Europan surface. Scientist believe that the lake,
covered by nearly 4 kilometers of ice, closely resembled the proposed
ocean on Jupiter's frozen moon. Both bodies of water seemed to have
formed by geothermal heating, and because the ice above is so thick,
both seas remained sealed from sunlight and air for millions of years.
Thus, if life exists in Lake Vostok (drilling missions have yet to
reach the liquid layer), it's plausible that life could also exist on
Europa.
However, scientists now believe that Vostok better resembles another
planet suspected of once harboring life: Mars. Natalia Duxbury (Jet
Propulsion Laboratory) and her colleagues suggest that Vostok did not
form by geothermal heating after all. Instead models of Vostok created
by the researchers imply that the Antarctic lake was originally an
open body of water that froze over between 5 and 30 million years ago.
And as such, any life found inside the lake would be older than the
Antarctic ice sheet.
This model bares a striking resemblance to the red planet. The Martian
north pole is known to be covered with ice. However, Mars's axial tilt
has changed dramatically throughout the planet's lifetime and the
current polar regions were once much warmer. Therefore it is easy to
assume that sometime in Martian history, the poles, like Duxbury's
model of Vostok, were once open bodies of water that later froze over.
Assuming life was present while Vostok was an exposed lake, and
assuming life is seen the lake today, it seems possible that if life
existed in an ancient Martian polar lake, it may still be there too.
The European Space Agency's Mars Express orbiter, scheduled for launch
in 2003, will examine the Martian poles for buried liquid water. A
similar experiment will eventually be flown to Europa as well. Details
of the study can be found in the January 25th Journal of Geophysical
Research.
PLUTO'S PALETTE REVEALED
During the 1980s Pluto and its satellite Charon repeatedly passed in
front of and behind one another as seen from Earth, a fortuitous
series of "mutual events" whose light curves allowed astronomers to
create crude maps of Pluto's surface. The maps showed that the half of
Pluto facing Charon was distinctly pink with a broad, dark belt
girding its midsection. Theorists surmised that the planet's
equatorial zone contained reddish organic byproducts derived from the
frosts of nitrogen, methane, and carbon monoxide that cover the
adjacent brighter regions.
However, when Eliot F. Young (Southwest Research Institute), Richard
F. Binzel (MIT), and Colorado high-school student Keenan Crane
analyzed four mutual events recorded in both blue and yellow light,
they got an unexpected surprise: the dark band actually consists of
separate blue and yellowish red regions. As the trio of researchers
report in the January issue of Astronomical Journal, these
variegations may indicate that bluish frosts are mixed with dark
material in varying amounts or that the equatorial belt has received
different amounts of heat and radiation to drive the organic reactions
in the icy surface.
COMET MCNAUGHT-HARTLEY HIGH IN HERCULES
Comet McNaught-Hartley (C/1999 T1) is still moving north, reaching yet
higher in the morning sky for the Northern Hemisphere. The
8th-magnitude comet rises around 11 p.m. for midnorthern latitudes and
is an easy target for binoculars as it moves through Hercules this
coming week. By the first light of dawn, the comet will be about 65
deg. above the eastern horizon. Here are positions for
McNaught-Hartley for 0 hours Universal Time in 2000.0 coordinates:
Date R.A. Dec.
Feb 17 17h 06m +30.4 deg.
Feb 19 17 12 +32.3
Feb 21 17 17 +34.1
Feb 23 17 22 +36.0
For details and a finder chart for the month of February, see the
Special Sky Events page at
http://www.skypub.com/sights/skyevents/0102skyevents.html .
THIS WEEK'S "SKY AT A GLANCE"
Some daily events in the changing sky, by the editors of Sky & Telescope.
FEB. 18 -- SUNDAY
* Some doorstep astronomy: This is the time of year when the bright
constellation Orion stands at its highest in the south in early evening.
Look for Orion's Belt, a diagonal row of three stars, in its middle.
FEB. 19 -- MONDAY
* Jupiter's Great Red Spot should cross Jupiter's central meridian (the
imaginary line down the center of the planet's disk from pole to pole)
around 11:01 p.m. EST. The "red" spot is currently very pale orange-tan. It
should be visible for at least 50 minutes before and after in a good 4- or
6-inch telescope if the atmospheric seeing is sharp and steady. For a list
of all predicted Red Spot transit times, see
http://www.skypub.com/sights/moonplanets/redspot.html .
* Jupiter's largest moon, Ganymede, casts its shadow on the planet from
9:42 to 11:55 p.m. EST.
FEB. 20 -- TUESDAY
* Mars is near Beta Scorpii this morning and Wednesday morning. Take a
look with binoculars! In a telescope, Beta is revealed as a fine double star.
FEB. 21 -- WEDNESDAY
* More doorstep astronomy: Once you've found Orion and his Belt high in
the south (see Sunday above), follow the line of the Belt to the lower left
for about two fist-widths at arm's length to find brilliant Sirius. In the
opposite direction, Orion's Belt points roughly to the group of bright
Jupiter, yellow Saturn, and orange Aldebaran.
FEB. 22 -- THURSDAY
* Jupiter's Red Spot transits around 8:32 p.m. EST.
FEB. 23 -- FRIDAY
* New Moon (exact at 3:21 a.m. EST this morning).
FEB. 24 -- SATURDAY
* Shortly after sunset, look just above the western horizon, far below
Venus, for the hairline crescent Moon.
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THIS WEEK'S PLANET ROUNDUP
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MERCURY is hidden deep in the glow of sunrise.
VENUS is the brilliant object (magnitude -4.6) shining in the west during
and after dusk.
MARS (magnitude +0.6, in the head of Scorpius) rises around 1 a.m. and
glows yellow-orange in the south before dawn. To its lower left is
similarly-colored Antares.
JUPITER and SATURN (magnitudes -2.4 and -0.2, respectively) shine brightly
high in the southwest to west during evening. Jupiter is the brightest;
yellowish Saturn is 8 degrees to Jupiter's lower right. To Jupiter's right
are the Pleiades, and farther to Jupiter's left or upper left sparkles
orange Aldebaran.
URANUS and NEPTUNE are hidden in the glare of the Sun.
PLUTO (magnitude 14; invisible without a large telescope) is in Ophiuchus
in the southeast before dawn.
(All descriptions that relate to the horizon or zenith -- including the
words up, down, right, and left -- 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 [GMT] minus 5
hours.)
More celestial events, sky maps, and news of the world's astronomy research
appear each month in SKY & TELESCOPE, the essential magazine of astronomy.
See our enormous Web site and astronomy bookstore at
http://www.skypub.com/.
Clear skies!
