Now awake, Philae may return the best comet science ever

Monday, June 15, 2015, 12:38 PM - Over the weekend, tiny comet lander Philae woke up after a nearly 8-month-long hibernation, reporting in twice to the Rosetta spacecraft and controllers here on Earth. So, what's next for this resilient robot?

After checking in on Saturday, for the first time since mid-November, the Rosetta mission's Philae lander called back on Sunday night, communicating with ground control for a total of about 4 minutes - from 5:22 to 5:26 p.m. EDT (23:22 to 23:26 CEST). During that time, the lander transmitted more data back to Earth, which the team is now examining, however according to Philae Lander Project Leader Stephan Ulamec, from the German Aerospace Center (DLR), "the connection to the lander was relatively unstable."

In an update on the DLR website, the team noted that the latest information from Philae indicates that it is in good health, is receiving at least 3 hours of sunshine every day, and is ready to continue operations. Connection strength appears to be dependent on Rosetta's orbit around the comet, so the spacecraft's trajectory will need to be adjusted to allow for longer communication times.

Once the connection is stronger, it's hoped that the team can retrieve the other 8000 or so data packets stored in Philae's memory, so they can determine what has happened since the lander woke up.

Discoveries so far

When it slipped into hibernation on November 15, 2014, the Rosetta mission's Philae lander had only been on the surface of Comet 67P/Churyumov-Gerasimenko for around 60 hours. While the science team had hoped for more time, this was just long enough to snap some pictures of its surroundings, and perform some quick tests of the comet's surface, its basic composition and - with the help of the spacecraft - the comet's interior structure.

Even the limited amount of data that Rosetta relayed back to Earth from the lander revealed some interesting and unexpected details about the comet.

• Rather than having a "fluffy" surface, which is why Philae was equipped with harpoons to anchor it, the dirty ice the lander came into contact with was quite hard - "a tough nut to crack" as the mission team called it,
• The interior structure of Comet 67P is 70-80 per cent "empty space" inside - highly porous dusty ice clumps with voids in between them,
• The ice under Philae is mostly water ice, rather than frozen carbon dioxide or other frozen gases, and
• The water that the ice is made up of is not like the water here on Earth, having a much higher ratio of heavy water to normal water than is found in our oceans.

With these discoveries made in just two and a half days, there is now plenty of time for Philae to conduct even more experiments, and the lander's period of hibernation has actually now extended this part of the mission months past its original timeline.

Philae's array of science instruments. Credit: ESA

"Bad Luck" turns to good?

If everything had gone as planned for Philae back on November 12, and it had secured its landing upon first touchdown, the Rosetta team expected to get roughly 4 months of operations out of the lander. According to their timeline, by March 2015, the temperatures inside Philae would have risen too high - due to the comet drawing closer to the Sun - for it to conduct experiments and gather data.

At the time of the landing, the bouncing journey Philae took across the surface of Comet 67P, resulting in it coming to rest in a shadowy depression in the terrain, was seen a bit of bad luck for the mission. However, now that the lander is getting enough sunlight to wake up and do science, it may be some time before it has any problems due to high temperatures, and it's possible it may be able to stay operational throughout the comet's closest approach to the Sun.

What's next?

So, with this stroke of good luck, what will the lander be doing next?

The very first thing the science team will do once communications between Philae and Rosetta are more stable is to determine how well the lander is functioning, including its 10 different science instruments.

"First, the non-mechanical instruments will be used - that is, instruments that do not drill or hammer," Ulamec explained in the update. This will begin with those instruments that consume the least power, and progress towards more energy-intensive ones, to determine exactly what kind of science Philae will be able to conduct.

If the full suite of instruments is at their disposal, the science team can then begin to schedule more experiments to test the surface composition in more detail, hammer through the surface layer to expose what's underneath, drill down to retrieve samples, analyze the gases streaming away from the surface, and pass more radio signals back and forth with Rosetta via their CONCERT instruments, to get an even more detailed look at the comet's internal structure.

An added bonus? With Philae potentially able to turn on its CONCERT instrument again, the mission team can use Rosetta to refine the triangulation of Philae's position - either verifying the current results of their search, or at least pinpointing the true location of where the lander came to rest.

Perhaps the most interesting aspect of the timing of Philae's renewed activity is that Comet 67P is now only 2 months away from perihelion - its closest approach to the Sun. At that time, on August 13, the comet will be over 185 million kilometres away from the Sun, and over 265 million kilometres from Earth. Far from being a "sungrazer" comet, 67P/Churyumov-Gerasimenko could provide the right environment for Philae to continue operating.

So, not only has Philae become the very first robot to land on the surface of a comet, it may also become the first to analyze a comet from the surface, as it passes through its period of greatest activity.

What more can the science team learn about Comet 67P? Given the unexpected discoveries so far, what they find could give us even more surprises!

For now, though, we need to give the Rosetta team the time they need to ensure Philae is truly up to the job.

Sources: DLR | ESA