Philae found? Rosetta's lost lander may have been spotted

Thursday, June 11, 2015, 2:35 PM - It's blurry and pixelated, but little comet lander Philae, lost since November of last year, may have just been spotted by the ESA's Rosetta team!

Ever since the Rosetta mission's Philae lander made history with its November 12 touchdown on Comet 67P/Churyumov-Gerasimenko, a quest began to pinpoint the exact location where it set down.

In the initial days after landing, it was simply to spot Philae for the purposes of modelling exactly how much sunlight the lander had access to, and thus judge how much time the science team had to gather data before the lander's batteries ran down.

Rosetta captured Philae's "triple landing", as it bounced across the surface of Comet 67P on November 12, 2014. Credit: ESA/Rosetta/MPS for OSIRIS Team MPS/UPD/LAM/IAA/SSO/INTA/UPM/DASP/IDA

After the lander went to sleep, it became about finding it to give the team some indication of the chances that Philae would get access to enough light as the comet swept closer to the Sun to recover and wake up again.

Since then, mission team members have pored over images snapped by Rosetta, especially those taken on its closest passes by the comet's surface, in an effort to gain any clues as to Philae's whereabouts.

As the image below shows, there were several promising candidates in the general vicinity of where Philae is thought to have touched down.

Five possible lander candidates identified by the Rosetta team. Credits: Centre image: ESA/Rosetta/NAVCAM – CC BY-SA IGO 3.0; insets: ESA/Rosetta/MPS for OSIRIS Team MPS/UPD/LAM/IAA/SSO/INTA/UPM/DASP/IDA

Added to this, the team also looked at the data from the radio signals passed back and forth between Rosetta and Philae, as their CONSERT instruments probed the interior structure of the comet. Since Rosetta intercepted Philae's CONSERT transmissions as it orbited around the comet, this data allowed the team to triangulate where those signals were being sent from, and it yielded an elliptical area where they could focus their search.

The CONCERT ellipse overlaid on top of Rosetta OSIRIS images. Credit: Ellipse: ESA/Rosetta/Philae/CONSERT; Image: ESA/Rosetta/MPS for OSIRIS Team MPS/UPD/LAM/IAA/SSO/INTA/UPM/DASP/IDA

Philae is that you?

With the chaotic collection of light and dark spots in the image, finding something artificial is no easy task. The key to figuring out if Philae is actually there was a comparison of images taken by Rosetta before the landing and those taken after, to notice if anything new showed up. Using images from October 22 and December 12-13, the team did notice something different.

Credit: ESA/Rosetta/MPS for OSIRIS Team MPS/UPD/LAM/IAA/SSO/INTA/UPM/DASP/IDA

Compare the bright spot in the middle of the centre and right-hand images, above, to the image to the right, which was taken during Philae's descent to the surface of Comet 67P on November 12.

That certainly does look like the lander!

The question now becomes ... is it actually the lander?

According to the ESA Rosetta blog, the team still can't be 100% certain at this time, and unless Philae wakes up sometime soon, there will be quite a wait before we can get further confirmation.

"Ultimately, a definitive identification of this or any other candidate as being Philae will require higher-resolution imaging, in turn meaning closer flybys," Rosetta blog editor Emily Baldwin wrote. "This may not be possible in the near-term, as issues encountered in navigating close to the comet mean that the opportunity to make flybys at significantly less than 20 km from the surface may be on hold until later in the mission. But after the comet’s activity has subsided, Rosetta should be able to safely operate in close proximity to the comet nucleus again."

The hope now is that, with the comet getting closer to the Sun for a mid-August perihelion, more sunlight will fall on Philae's solar panels, charging the lander's batteries and allowing it to wake up. There have already been three attempts to pick up the lander's signal (should it be broadcasting) - in mid-March, mid-April and early May - however there's been nothing from Philae so far. Further attempts will be made, however if Philae is still silent through August, the chances of hearing from it ever again are likely very slim. It's possible that the lander's location simply does not receive enough light, no matter how close it gets to the Sun, or it could be that the extreme cold has rendered Philae's systems inoperative.

Until that time, though, the search for Philae remains a priority.

"Accurately locating the lander is of great scientific value, in particular for the joint orbiter and lander CONSERT experiment to get the best assessment of the interior structure of the comet nucleus," said Matt Taylor, ESA’s Rosetta project scientist. "Knowing where Philae is would provide important context for the lander measurements and valuable information for its possible future operation. In the meantime, Rosetta is continuing to observe the comet from a range of distances as the comet’s activity increases."

Source: ESA Rosetta blog