Rosetta is listening for signs of life as Philae sleeps (Wired UK)


Two images from Rosetta’s navigation camera (NAVCAM) show the spot where it is thought Philae first touched down, raising a dark cloud of dust

ESA/Rosetta/NAVCAM – CC BY-SA IGO 3.0


Rosetta space scientists are thrilled that its tiny comet lander
Philae beat all the odds to complete its primary mission, returning
data from all its on-board experiments before its main battery
failed. The plucky probe did all that was expected of it in the
initial phase of the mission during 57 hours sitting on the surface
of Comet 67P/Churyumov-Gerasimenko.  As we have
previously reported, Philae itself has not died but is now in
a state of hibernation and could be re-awoken in the weeks or
months ahead if it receives enough sunlight. The European Space
Agency mission team are still uncertain whether this will happen,
mainly because they still do not know exactly where Philae ended up
on the comet.  But they revealed they had imaged the probe and
its shadow during its first bounce.  


New analysis of an image of the comet shows Philae and its shadow

ESA/Rosetta/NAVCAM


After its harpoons failed to fire, the washing machine-sized
probe bounced twice before becoming lodged against a cliff that is
blocking the Sun’s rays. It was getting just 1.5 hours of sunlight
every 12 hours when it needed six or seven hours for the secondary
batteries to charge up and keep Philae awake.  During the
coming days and weeks, mission controllers will continue to listen
for any signals from the lander as its Rosetta mothership flies
overhead in orbit around the comet. In Philae’s favour, it is being
carried closer to the Sun and will also experience a seasonal
change that may deliver more solar power. However the comet will
also become more active and produce more “sublimation”-the process
where its ice turns to jets of vapour, which could surround Philae
with clouds of gas and dust. Asked if Philae could wake up, Comet
expert Professor Alan Fitzsimmons, of Queen’s University Belfast,
said today: “In terms of sunlight there are two positives. First,
as the comet approaches the Sun, the inverse square law means that
the flux (amount of sunlight) on the solar arrays will increase. By
late March next year this will have doubled, so in theory twice as
much power can be delivered by the solar arrays.  


A labelled trajectory of Rosetta’s orbit, following the comet landing on 12 November

ESA


“Second, the orientation of the spin axis means right now the
comet is experiencing “Northern” summer. Next spring/summer the Sun
will be near equatorial. This might shorten the maximum length of
the shadows on the comet near Philae and increase the exposure time
on the solar panels.” But Professor Fitzsimmons added that there
were two negatives. He said:  “The local geology may mean that
Philae does not get an increased amount of sunlight as the comet
moves from Northern summer. More importantly, the comet is active
with increasing sublimation of surface/subsurface ice, increasing
the dust environment around the nucleus.  “Also the surface
undergoes active erosion with landslides and subsidence clearly
visible in the Rosetta images. Ground-based data from the last
orbit showed a major sublimation site may start up next year near
the equator. So in summary, no-one knows right now.” Mission
controllers hope that they have stacked the odds in Philae’s favour
by lifting the lander’s main body by 4cm and rotating it about 35°,
along with its fixed solar panels before power was lost. 
Stephan Ulamec, who was lander manager at ESA’s Space Operations
Centre (ESOC) in Darmstadt, Germany, this week said: “It has been a
huge success, the whole team is delighted. “Despite the unplanned
series of three touchdowns, all of our instruments could be
operated and now it’s time to see what we’ve got.” During coming
months, scientists around the world will be poring over the mass of
data returned from Philae’s ten experiments, including its
drill which bit into the crumbly surface before hitting something
more solid. In the meantime, mothership Rosetta is still
performing superbly. Having despatched Philae, it is now moving out
to an orbit 30km from the comet, but will return to a 20km orbit on
6 December as it watches the comet warm and become active on its
journey into the Solar System. In a statement, Matt Taylor, ESA’s
Rosetta project scientist, said: “The data collected by Philae and
Rosetta is set to make this mission a game-changer in cometary
science.” Fred Jansen, ESA’s Rosetta mission manager, said: “At the
end of this amazing roller-coaster week, we look back on a
successful first-ever soft-landing on a comet. This was a truly
historic moment for ESA and its partners.  “We now look
forward to many more months of exciting Rosetta science and
possibly a return of Philae from hibernation at some point in
time.” 

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originally appeared on Sen

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17 November 2014 | 10:58 am – Source: wired.co.uk

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