12/28/2007: For Astronomers; The Solar System exploration in 2007:

Surprises abounded in the solar system in 2007. A meteorite crashed to
Earth in Peru and left some unsolved mysteries, a massive dust storm
erupted on Mars and threatened NASA's robotic rovers, and an obscure
comet suddenly brightened by a factor of a million and became visible
to the naked eye. t was an exciting year for comets and asteroids.
Scientists discovered a new family of asteroids to which the asteroid
that killed off the dinosaurs appears to belong. The Baptistina
asteroids are fragments of a huge 170-kilometre-wide asteroid that
shattered into pieces in a collision 160 million years ago, with one
of the fragments later slamming into Earth and wiping out T. rex.

Speculation about the cause of a a crater that appeared in the
countryside of Peru on 15 September ended when an expedition of
scientists found fragments of a stony meteorite at the site. But
experts were still puzzled over some aspects of the crash, including
how the meteorite had remained in one piece without breaking apart in
the atmosphere.

A normally very dim comet called Comet Holmes unexpectedly brightened
by a factor of a million in a period of just 36 hours in October. The
outburst made it temporarily visible to the naked eye and may have
been due to a crack opening up in the comet's nucleus and expelling
clouds of gas and dust.

A rare meteor shower called the alpha Aurigids, which had previously
been seen only three times in history, returned to wow skygazers in
September 2007. Unlike most meteor showers, which are due to comets
with short periods, the alpha Aurigids are due to debris from a long-
period comet that takes 2000 years to orbit the Sun.

Japan's Hayabusa spacecraft gegan limping back to Earth. Scientists
still hope that it might contain a sample of material from asteroid
Itokawa, despite serious problems during the collection process.

NASA's Dawn spacecraft launched in September. It will reach the
asteroids Vesta in 2011 and Ceres in 2015.

The newly launched STEREO spacecraft allowed scientists to witness a
comet getting its tail ripped off by a solar outburst, something
inferred from previous observations, but never seen directly.

Mars continued to be the most intensely studied planet aside from
Earth, with rovers crawling over its surface and spacecraft analysing
it from orbit.

NASA's Spirit rover accidentally revealed an important clue to Mars's
past when one of its wheels, which has been unable to turn since 2006,
ploughed up a patch of soil while being dragged along during a drive,
revealing silicate rich soil. Silicates form in the presence of hot
water, and rover scientists pointed to the soil as evidence that
volcanic activity once sent hot water or steam percolating through the
soil at the site, making it a potential habitat for life at the time.

Severe dust storms erupted on Mars in mid-2007, threatening to reduce
the rovers' solar power enough that one of them might freeze to death.
By September, however, skies were clear enough for Opportunity to
start its long awaited drive into the giant crater Victoria.

Meanwhile, analysis of Martian clays from orbit suggested that Mars
was not as warm and wet in its past as previously believed, though
radar observations hinted at vast stores of water ice on the planet's
equator.

And NASA's Phoenix Mars lander blasted off in August. Phoenix is
expected to touch down in May 2008 to determine whether the soil has
thawed in the recent past and to look for organic molecules that could
signal past or present life.

At Saturn, the Cassini spacecraft again returned a wealth of results
on the ringed planet and its moons. Scientists struggled to explain a
bizarre hexagon shaped clearing in the clouds of Saturn's north pole.

It also found what appears to be a lake of liquid methane or ethane
the size of Earth's Caspian sea on Saturn's moon, Titan, the largest
lake found there so far. And a new analysis of radio data from the
Huygens lander that touched down on Titan in 2005 revealed tentative
signs that there could be an ocean of liquid water beneath the moon's
surface.

Cassini's close flyby of Saturn's walnut-shaped moon, Iapetus,
revealed that it is spotted like a Dalmatian, apparently because dark
material that splattered onto its face from other moons got warmer
than lighter material, creating a feedback loop of ice sublimation.

Finally, scientists proposed that the bizarre spongy appearance of
Saturn's moon Hyperion is due to the moon's high porosity, with 42%% of
its volume being empty space.

The Moon was a hot target in 2007, with both Japan and China sending
robotic orbiters there.

Japan's Kaguya spacecraft launched towards the Moon in September.
After reaching orbit in October, it beamed back high-definition videos
of the Moon's surface and Eartrise, and released two smaller probes to
help measure the Moon's lumpy gravity field.

China launched its first spacecraft beyond Earth orbit, hurling its
Chang'e 1 probe towards the Moon in October. The spacecraft reached
lunar orbit in November. Internet gossip suggested the spacecraft's
first publicly released image of the Moon was a fake, but a careful
analysis confirmed it to be genuine.

NASA announced it would also send another robotic spacecraft called
GRAIL to the Moon in 2011 to obtain better gravity field measurements
than Kaguya, in addition to its Lunar Reconnaissance Orbiter already
set for launch in 2008.

Jupiter had a visit in February by the New Horizons spacecraft for a
gravity boost en route to Pluto. New Horizons obtained a movie of a
volcanic plume spurting from Jupiter's moon, Io.

A curious lack of moons smaller than 16 kilometres across hinted that
Jupiter's smallest satellites may have eroded away. The Hubble Space
Telescope, making its own observations of Jupiter from Earth orbit,
observed mysterious and dramatic changes to Jupiters striped.

Finally, the Voyager 2 spacecraft reached a solar system boundary
called the termination shock 30 years after being launched, a
threshold crossed by the Voyager 1 spacecraft in 2004.