Efforts to find Europe's lost
comet lander, Philae, have come up
blank.
The most recent imaging search by
the overflying Rosetta
"mothership" can find no trace of the probe.
Philae touched down on 67P/Churyumov-Gerasimenko
on 12 November, returning a swathe of data before going silent when its battery
ran flat.
European Space Agency scientists
say they are now waiting on Philae itself to reveal its position when it
garners enough power to call home.
Researchers have a pretty good
idea of where the robot should be, but pinpointing its exact location is
tricky.
On touchdown, Philae bounced
twice before coming to rest in a dark ditch.
This much is clear from the
pictures it took of its surroundings. And this location, the mission team
believes, is just off the top of the "head" of the duck-shaped comet.
The orbiting Rosetta satellite
photographed this general location on 12, 13 and 14 December, with each image
then scanned by eye for any bright pixels that might be Philae. But no positive
detection has yet been made.
Rosetta has now moved further
from 67P, raising its altitude from 20km to 30km, and there is no immediate
plan to go back down (certainly, not to image Philae's likely location).
Even if they cannot locate it,
scientists are confident the little probe will eventually make its whereabouts
known.
As 67P moves closer to the Sun,
lighting conditions for the robot should improve, allowing its solar cells to
recharge the battery system.
The latest assessment suggests
communications could be re-established in the May/June timeframe, with Philae
distributing enough electricity to its instruments to resume operations around
September.
This would be at perihelion - the
time when the comet is closest to the Sun (185 million km away) and at its most
active.
Scientists continue to pore over
the data Philae managed to send back before going into hibernation.
Some of the results - together
with ongoing Rosetta observations - were reported at the recent American
Geophysical Union meeting in San Francisco.
Highlights include a clearer idea
of the nature of the comet's surface. Researchers say this appears to be
covered in many places by a soft, dusty "soil" about 15-20cm in
depth.
Underneath this is a very hard
layer, which is thought to be mainly sintered ice.
The conference had the rare
opportunity to see pictures from Rosetta's Osiris camera system.
These high-resolution images are
not normally shown publicly because the camera team has been given an exclusive
period to study the data and make discoveries.
Among them was a shot looking
into a pit on the surface, revealing an array of rounded features that the
Osiris team has nicknamed "dinosaur eggs".
These features have a preferred
scale of about 2-3m and may be evidence of the original icy blocks that came
together 4.5 billion years ago to build the comet.
The dino eggs have been seen at a
number of locations, including in cliff walls.
Early interpretations of the
general surface of the comet indicate that many structures are probably the
result of collapse over internal voids.
Although a small body just 4km
across, 67P's gravity is still strong enough to shape depressions and arrange
fallen boulders.
A good example of this is in
"Hapi" valley - the giant gorge that forms the "neck" of
the comet.
It contains a string of large
blocks at its base, which one Osiris team-member argued very likely fell from
the nearby vertical cliff dubbed "Hathor".
All the surface features on 67P
carry names that follow an ancient Egyptian theme.
Hapi was revered as a god of the
Nile. Hathor was a deity associated with the sky.
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