This past weekend, the Philae Lander awoke from its 211-day hibernation on Comet 67P/Churyumov–Gerasimenko. The dramatic receipt of signals from the probe triggered renewed activity among mission planners who are now trying to figure out what to do next. Here’s how things could unfold.
Top image: The comet as seen on June 13, just a few moments before Philae’s wake-up signal was received.
To quickly recap, the Philae Lander, after settling in a shaded area of the comet, ran out of power on November 15, 2014. Some four months later, the comet’s environmental conditions began to change, including higher surface temperatures and improved illumination. Accordingly, mission controllers periodically flipped Rosetta’s receiver to the on position in hopes of receiving a signal from Philae at optimal times.
“No Apparent Degradation”
This past weekend it finally happened, not once, but twice. On June 13, a weak but solid radio link between Rosetta and the Lander was established for 85 seconds. During that time, more than 300 data packets totaling 663 kbits of lander diagnostics and telemetry were received. This signal was in turn relayed by Rosetta to ESA’s European Space Operations in Germany. The next day, a second, smaller burst of lander data was received. Philae is currently reporting an internal temperature of –5ºC (23ºF).
Philae is somewhere around here. (ESA/Rosetta/MPS for OSIRIS Team MPS/UPD/LAM/IAA/SSO/INTA/UPM/DASP/IDA)
“[We] can already tell that all lander subsystems are working nominally, with no apparent degradation after more than half a year hiding out on the comet’s frozen surface,” noted Philae Lander Project Manager Stephan Ulamec in a statement. “While the information we have is very preliminary, it appears that the lander is in as good a condition as we could have hoped.”
The ESA says that Philae has stored over 8,000 packets of additional status data over an undisclosed period. The space agency would very much like to get their hands on this precious information, but it’s not clear if they ever will.
The First Stage of the Next Phase
Encouragingly, the lander is now getting enough sunlight to heat it to a functional operating temperature and to generate electricity. Its solar panels are now receiving power for over 135 minutes during each illumination period. That’s nearly twice the amount it was receiving back in November.
Among the most important next steps is to determine how to optimize Rosetta’s orbit to improve contact with the lander and to enable ongoing science investigations. The lander itself is thought to have sufficient energy to perform low-power measurements (i.e., through the use of non-mechanical instruments), including some that weren’t made during its initial 60-hour stint. At this point, drilling into the comet is not deemed a viable option.
It’s critical, however, that a more robust link be established between the lander and its orbiter.
Rosetta’s new orbit, scheduled to last from June 16 to 19, will see it move 12 miles (20 km) closer to the comet, down to a distance of about 180 km (110 miles) from the surface. The orbiter will be configured such that it will continuously point its communications unit at the comet. Ideally, the ESA planners would like to move it even closer. Trouble is, rising temperatures at the comet’s nucleus have activated jets of vapor and dust. It’s starting to become a dangerous environment for Rosetta.
Computer generated impression of Philae’s landing. (ESA)
“If we manage to achieve and maintain a predictable contact pattern, the lander teams can devise a strategy for a new sequence of scientific operations,” noted Rosetta team member Paolo Ferri. “Regardless, we will stay very flexible and be ready to react quickly. It’s clear this incredible mission continues to stimulate and challenge us, developing in ways we could never have predicted.”
Rosetta could receive its next communications signal from Philae on Friday, while science experiments could commence in less than a week.
And the timing couldn’t have been better. The comet will reach its perihelion on August 13 — its closest point to the Sun along its orbit — during which time its surface will become particularly active.
“We know now that we can get in touch with Philae,” said Jean-Jacques Dordain, ESA’s director general, during a press conference on Monday. “It will be getting warmer and warmer on the surface of the comet because, until the 13th of August, the comet will get closer and closer to the sun, so we should have more and more opportunities to get in touch with Philae.”
It’s also worth pointing out that, had Philae’s landing been successful back in November, the mission would have expired in March. Depending on what happens next, this may have been an enormous stroke of luck.