Topic: Late August Astronomy Bulletin

[Clive]

MARTIAN METHANE NOT UNDERSTOOD
ESA

The discovery some years ago of methane in the Martian atmosphere
was a surprise.  Much of the methane in the Earth's atmosphere is of
biological origin, but some is contributed by vulcanism.  Methane is
thought to be stable in the Martian atmosphere for around 300 years.
It follows that the observed methane must have been generated within
the last few hundred years.  Recently, people at Goddard Space Flight
Center have said that the methane that they saw in 2003 was
concentrated in three particular regions.  That showed that it must
have been released so recently that it had not had time to distribute
itself around the planet.  Moreover, instead of taking 300 years to
disappear, it had almost entirely vanished by early 2006.  Now,
atmospheric physicists have tried to model Mars' climate, but their
models are unable to reproduce the behaviour of the methane.
Something seems to be removing the methane from the atmosphere 600
times faster than the models can account for.  That might suggest that
the source must be 600 times more intense than was originally assumed,
which is considerable even by terrestrial standards.


TRIPLE ASTEROID SYSTEM
NASA/Jet Propulsion Laboratory

Radar imaging has shown that near-Earth asteroid 1994 CC, which came
within 2.52 million kilometres of the Earth on June 10, is a triple
system, only the second triple system known in the near-Earth
population.  It consists of an object about 700 metres in diameter
that has two smaller bodies, probably at least 50 metres in diameter,
revolving around it.  The next comparable Earth fly-by for asteroid
1994 CC will occur in 2074, at a distance of 2.5 million kilometres.


CASSINI DISCOVERS NEW OBJECT IN SATURN'S RINGS
JPL

The Cassini spacecraft has discovered a new object in Saturn's rings.
As the Sun shone onto the rings almost edgewise as the planet neared
its August 11 equinox, Cassini observed the 25-mile-long shadow cast
on Saturn's B ring by a tiny moonlet that is probably about a quarter
of a mile in diameter.


TRACES OF PLANET COLLISION FOUND
NASA/JPL

The Spitzer space telescope has found evidence of a high-speed
collision between two objects orbiting around a young star called
HD 172555, still in the early stages of planet formation.  The star
is about 100 light-years away in the far-southern constellation Pavo,
and is considered to be about 12 million years old.  Astronomers
believe that two rocky bodies, one at least as big as Mercury and the
other at least as big as the Moon, slammed into each other within the
last few thousand years or so -- very recently by cosmic standards.
The impact destroyed the smaller body, vaporizing huge amounts of rock
and flinging massive plumes of hot lava into space.  The collision
would have had to be between substantial bodies and at a high speed
for rock to have been vaporized and melted.  It would be a rare event,
but critical in the formation of Earth-like planets and moons.  It
might be analogous to the one that has been speculated to have formed
our Moon more than 4 billion years ago, by the collision with the
Earth of a body the size of Mars.  Such violence is thought to be a
routine aspect of planet-building.  The most popular theory at present
is that rocky planets form and grow in size by colliding and sticking
together, merging their cores and shedding some of their surfaces.
Even though things have settled down in our Solar System today,
impacts do still occur, as was observed only last month after a small
object of some sort crashed into Jupiter.

The infrared spectra taken by Spitzer have been interpreted as
demonstrating lots of amorphous silica, essentially melted glass.
Silica can be found on Earth in obsidian rocks and tektites.  Obsidian
is black, shiny volcanic glass.  Tektites are hardened chunks of lava
that are thought to form when meteorites hit the Earth.  Large
quantities of silicon monoxide gas were also detected, presumed to
have been created when a lot of the rock was vaporized.  In addition,
the astronomers considered that the information from Spitzer included
evidence of rocky rubble, The mass estimated for the material and gas
observed suggests that the combined mass of the two colliding bodies
was more than twice that of our Moon.  The two bodies would have been
travelling at a relative velocity of at least 10 km/s before the
collision.


IN SEARCH OF ANTIMATTER GALAXIES
NASA

With only about half a dozen more Shuttle flights to come, crews will
add further units to the International Space Station, bringing to an
end twelve years' US contributions to the orbital construction.  A
flight near the end of the programme in 2010 will deliver the 'Alpha
Magnetic Spectrometer' (AMS) cosmic-ray detector that will hunt for
anti-matter galaxies.  In addition to sensing distant galaxies made
entirely of anti-matter (if such a thing were to exist), the AMS will
test theories of dark matter and search for 'strangelets', a highly
speculative form of matter.  Some understanding of strangelets might
help scientists to study micro-quasars and tiny, primordial blacks
holes as they evaporate, thus proving whether such small black holes
even exist.  All such exotic phenomena might make their presence known
by the ultra-high-energy cosmic rays that they might emit -- the type
of particles AMS is intended to detect.

According to physicists' models, the Big Bang ought to have produced
just as much antimatter as matter -- but we do not see any.  It can't
be nearby, because if it were, we would see bright X-ray emissions
where the antimatter came into contact with matter and annihilated.
One, albeit far-fetched, explanation could be that some distant
galaxies are made entirely of antimatter instead of matter.  Since
antimatter wouldn't look any different from ordinary matter,
astronomers would not be able to tell whether a distant galaxy were
made of matter or antimatter just by looking at it.  However, AMS
would produce evidence of antimatter galaxies if it detected even a
single nucleus of anti-helium or a heavier antimatter element.
Collisions among cosmic rays near the Earth can produce antimatter
particles, but the odds against such collisions producing an intact
anti-helium nucleus are so vast that finding even one such nucleus
would strongly suggest that it must have come from a distant region
of the Universe dominated by antimatter -- truly a case of one swallow
implying a whole summer!

Other instruments such as the Italian PAMELA satellite have looked for
anti-helium nuclei, but none has been sensitive enough to rule out the
existence of antimatter galaxies.  AMS has about 200 times the
particle-collecting power of anything that has flown before.  If AMS
detects no anti-helium nuclei, even the diehards will have to accept
that there are no antimatter galaxies within about 1000 megaparsecs --
roughly to the edge of the observable Universe.