Comet 67P on 12 September
ESA/Rosetta/MPS for OSIRIS Team MPS/UPD/LAM/IAA/SSO/INTA/UPM/DASP/IDASomewhere dark and icy on a comet 320 million miles away, the
history-making, comet-bouncing Philae spacecraft is sleeping. Its
batteries are depleted and there isn't enough sunlight to recharge.
But while the lander finished its primary job, collecting
invaluable data on the surface of comet 67P/Churyumov-Gerasimenko,
the Rosetta mission is far from over. For many scientists, the
excitement is just beginning.
Philae's landing two weeks ago was a wild one. The washing-machine sized spacecraft dropped right
onto its intended landing site, but the harpoons designed to anchor
it into the ground didn't fire. Without anything to latch onto the
surface, the spacecraft bounced back up a kilometer into space,
soaring for nearly two hours before returning to the ground. After
another smaller bounce, Philae settled somewhere in the shadow of a
cliff, at least 1 kilometer from where it was supposed to
be.
Mission engineers are now scouring the comet for signs of the
lander. They're using the OSIRIS camera onboard the Rosetta
spacecraft that's orbiting the comet to look for any glint of
brightness reflected by Philae, says planetary scientist Sebastien
Besse, a member of the OSIRIS team. They're also using data from
the CONSERT instruments on Rosetta and Philae, which
send radio signals between the two spacecraft, to triangulate
the lander's location.
From left to right the new images show Philae's descent towards 67P before bouncing off in an easterly direction
ESA/Rosetta/MPS for OSIRIS Team MPS/UPD/LAM/IAA/SSO/INTA/UPM/DASP/IDAOnce they find Philae, mission engineers can better assess the
chances that it will eventually receive enough sunlight to
recharge, wake up, and do more science. "The chances seem
reasonably good," said Mike A'Hearn, a planetary scientist from the
University of Maryland and a member of the Rosetta science team. So
far, the team has narrowed down Philae's location to a sliver about 100 feet
wide and 1,150 feet long near a depression on the south side of the
comet, where it's now winter.
But summer is coming. Over the next few months, the changing
seasons will bring more direct sunlight onto Philae. The comet is
also moving toward the sun, and the hope is that in the next few
months, both the coming summer and increasing proximity to the
sun will give Philae the warmth and power it needs to wake up.
Mission controllers have done everything possible to give Philae a
chance, Besse says. Before Philae shut down, they rotated the
lander 35 degrees to orient its solar panels toward the sun.
For now, all we can do is wait. "I'm very confident that
Philae will resume contact with us and that we will be able to
operate instruments again," said lander team leader Stephan Ulamec
in a statement on Nov. 17.
Of course, there's a lot of uncertainty, and Philae will
need quite a bit of luck, Besse says. Still, the team is hopeful.
"In this business, you have to be optimistic," he said.
Preliminary Results
Despite the unexpected triple landing and its current MIA
status, Philae did the science it was supposed to do. It ran its
preprogrammed sequence of commands and started collecting data with
its suite of instruments, sniffing, hammering, drilling, and even
listening to the comet. Powered by only 60 hours of battery life
and with its ability to recharge in doubt, Philae beat the clock
and sent all the data back to Earth before its battery petered
out.
Scientists are still busy analysing the bounty of data, but
they've already released some preliminary results. Philae has detected organic
molecules, which are necessary for life. One of the reasons
scientists want to study comets is that the icy bodies could have
delivered the organics and complex molecules needed for life when
they slammed into the planet early in its history.
Past comet missions and ground-based telescopes have seen dozens
of molecules on comets, including organics. For example,
this summer, the Atacama Large Millimeter/submillimeter Array
telescope in Chile found
organic molecules in the atmosphere of comets ISON and
Lemmon. But what kind of molecules did Philae detect? That
remains to be seen.
One instrument enabled Philae to hammer into the ground and find
that the surface underneath the lander is surprisingly hard, likely
made of ice. Philae also measured vibrations created when the feet
of the lander hit the ground on the first landing, producing
the first-ever
audio recording of a comet touchdown. An analysis of the
recording suggests a layer of soft dust sits on top of the hard,
icy surface.
The lander was also supposed to drill into the comet and deliver
samples into its ovens, which would analyse the chemical
composition of samples. Both the drill and the ovens worked
perfectly, but it's unclear whether Philae was able to drill anything at all. The
team is still analysing the data to see what, if anything, the
ovens measured. Initial indications don't look good, however.
According to a tweet on Nov. 17 from Science magazine's
Eric Hand, Fred Goesmann of the Max Planck Institute for Solar
System Research and leader of the COSAC instrument said that the
drill didn't deliver any samples into the ovens. "There's nothing
in it," Goesmann was quoted as saying.
Indeed, the botched landing did compromise some of the science.
For instance, accelerometers and thermometers on the harpoons never
deployed, so couldn't gather any data. "It's unfortunate the lander
didn't do exactly what it was supposed to do," said planetary
scientist Anita Cochran of the University of Texas at Austin, who
is not a part of the Rosetta mission. Still, she says, Philae got
loads of important information. "Whatever they get is way more than
we had," she said.
Watching a Changing Comet
In the days surrounding Philae's landing, the Rosetta spacecraft
collected scientific data from afar. Much of those results have
been submitted into scientific journals and will likely be
published in the next couple weeks, Besse says. But Rosetta's main
job has been to support Philae, scouting out possible landing
sites, and watching over the lander as it settled onto the comet.
Now, the real science begins for Rosetta.
As part of a maneuver to adjust its orbit, the spacecraft will
fire its thrusters to lift it to 19 miles from the comet. On Dec.
3, it will move closer until it's 12.5 miles away. Rosetta will
remain in orbit, watching the comet come to life as it approaches
the sun, reaching its closest point in mid-August. The ices on the
comet will heat up, sublimating into gases that are ejected into
space. The rubber-duck-shaped chunk of ice and dust will be
enshrouded in a haze of dust and gas called the coma. The sunlight
will push the dust and gases away and form the comet's tail.
And Rosetta will be right there watching the action.
This incredible image was taken by the Philae lander of one of its legs resting on the comet's surface
ESA/Rosetta/Philae/CivaPreviously, spacecraft have visited seven different comets, but
nearly all missions were quick flybys. In 2005, the Deep Impact
mission fired an impactor into comet Tempel 1, blasting a cloud of
debris that could then be analysed. The Stardust spacecraft, which
went to comet Wild 2 in 1999 and grabbed a sample of its tail to
return to Earth, swung by comet Tempel 1 in 2011 for a closer look
at the crater created by Deep Impact.
All these missions studied a comet at a single point in time,
capturing just a snapshot. But comets are dynamic objects; their
characteristics are defined by change. They suddenly appear in the
sky, growing brighter and brighter, its tail stretching longer and
longer. Then, just as sudden as they appeared, they shrink and
fade. Now, for the first time, Rosetta will be able to observe what
is actually happening on the comet up close.
For example, Rosetta will be able to see how exactly dust and
gas escapes the comet and how this varies from place to place, says
A'Hearn. In doing so, scientists can distinguish features that are
due to the comet's evolution over time from primordial features
that were a part of the comet since its formation. Pinpointing
those properties, A'Hearn says, is essential for understanding how
comets form, the history of the solar system, and whether comets
could have delivered the chemicals needed for life on Earth.
Rosetta will also probe the interior of the comet, mapping the
different layers of ice and dust and how its density varies.
Another question, Cochran says, is how comet 67P's shape will
change over time. Will the neck connecting the two lobes whittle
away? Will the comet eventually split apart? Is the comet the
result of two pieces that stuck together?
Rosetta's mission will continue until December 2015, following
comet 67P as it swings back away from the sun. The hope is that the
spacecraft will keep working deep into 2016. But that will depend
on the unpredictable volatility of the comet, Besse says. Dust
particles expelled by the comet could damage the spacecraft. The
comet could belch out gas that blows Rosetta off course. Or,
Rosetta could just wear down. It is, after all, already 10 years
old. In that time, many of us have already gone through several
computers and phones. But so far, Besse says, Rosetta seems to be
in great shape.
Future Missions
So we've landed on a comet. And we're now orbiting one for the
first time. What's next? Scientists are already planning future
comet missions, which most likely will involve another lander at
the very least. One idea is for a spacecraft to hop from place to
place on a comet-this time, on purpose-and study differences on the
surface. One such proposed mission, the Comet Hopper, made it to
the final rounds of NASA's selection process in 2012 before losing
out to a Mars
lander called InSight, which is slated for launch in
2016.
Missions like Comet Hopper and Deep Impact were NASA Discovery
missions, which are intended to be faster and cheaper projects. For
the next Discovery mission, there are at least three proposals for
sending a spacecraft to a comet, says A'Hearn, who led the Deep
Impact mission and was a part of the Comet Hopper proposal.
This image of comet Tempel 1 was taken 67 seconds after it was hit by Deep Impact’s impacter
NASA/JPL-Caltech/UMDBut what comet scientists would really want is a sample return
mission: Send a spacecraft that could grab a chunk of comet and
send it back to Earth. The kinds of experiments you can do in
Earth-bound labs are much more sophisticated than anything onboard
a spacecraft, Cochran says. But such a mission would be difficult
and expensive. For example, Besse adds, you would have to build a
cryogenic capsule to keep your comet stuff cold. And comets are
cold. In August, Rosetta measured comet 67P's average temperature
to be -94 degrees Fahrenheit (-70 degrees Celsius).
Because of the added complexity and expense, a sample return
mission would have to be one of NASA's higher-cost New Frontiers
missions. One of those missions, New Horizons, will begin exploring
Pluto and its moons in 2015. Another, Juno, will arrive at Jupiter
in 2016. "I expect that there will be at least two separate
proposals for a comet surface sample return mission in the next
round of New Frontiers," A'Hearn said. These future missions will
be needed, he says. Rosetta will answer many questions about
comets, but it will also raise many more.
Until then, Rosetta has centre stage. And the show is about to
begin.
This story originally appeared on Wired.com
Source Article from http://www.wired.co.uk/news/archive/2014-11/26/rosetta-future-comet-missions http://cdni.wired.co.uk/1920x1280/a_c/67p.jpg
What's next for Rosetta and future comet exploration?
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