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Emily LakdawallaNovember 13, 2014

Philae status, a day later

The Philae team scrambled all morning to comprehend the initially confusing status of the lander, and the picture is much clearer today. But I can't talk about clear pictures without showing you the best thing from this afternoon's press briefing, an animated gif of the descending Philae, captured by the OSIRIS camera:

Philae falling


Philae falling
This animation shows the Philae lander falling away from Rosetta from 10:24 to 14:24 on November 12, 2014, in images taken an hour apart, beginning about two hours after the spacecraft separated at 08:35.

I now appreciate why there was so much confusion yesterday. When Philae initially touched down, that triggered the end of its descent sequence and the start of its first block of science activity. Its instruments dutifully performed their measurements and Philae relayed these back to the orbiter -- all while Philae was steadily climbing away from the comet at a speed of 38 centimeters per second. At the same time, the internal flywheel was slowly being braked, and that caused Philae to rotate, which was incredibly confusing to a team that thought the spacecraft was stationary on the comet surface.

Here are a few bullet points from the press briefing:

Here are few more bullet points on spacecraft activity and status from an ESA update:

Where is the lander on the comet? They don't know yet. They think they know approximately where it is, thanks to data from the CONSERT instrument. But at least one member of the science team disagrees with this assessment; Holger Sierks thinks it's about the same distance away from the initial landing site, but in a 10:00 direction rather than a 3:00 direction.

Where did Philae land?


Where did Philae land?
Where did Philae land? Its initial impact point is precisely located within the red square. Its final landing location is not yet known, but CONSERT radar sounder data suggests it is somewhere within the blue diamond.

I was initially surprised by this location because it is located prograde (in a rotational sense) from the touchdown site, but after a little further thought I think it makes sense. Here's the important detail: When Philae was descending, it was in an elliptical orbit around the center of gravity of the comet. That orbit intersected the ground at the intended landing site in such a way that the horizontal component of Philae's motion was parallel to the orbital motion of the surface at that point, which is another way of saying that the spacecraft landed vertically. (Mission manager Stephan Ulamec described this geometry in a press briefing earlier this week.) So when it bounced off, it bounced off close to vertically in the reference frame of the comet's surface, and then when it landed it landed a relatively short horizontal distance away from the initial impact site. (By this logic, either the blue diamond location from CONSERT or Sierks' location makes equal sense.)

They had representatives from all the camera teams -- Jean-Pierre Bibring for CIVA, Holger Sierks for OSIRIS, and Stefano Mottola for ROLIS. Mottola showed a ROLIS image captured just 40 meters above the very first impact point. Mottola said the gravels at the initial impact site ranged in size from millimeters to meters in diameter. He pointed at a small boulder in the upper right of the image and mentioned the dust that appeared at its base; he said it is not clear whether the dust is accumulating at the base, or if the rock is being exposed by sublimation.

ROLIS view of Churyumov-Gerasimenko from 40 meters altitude

ESA / Rosetta / Philae / ROLIS / DLR

ROLIS view of Churyumov-Gerasimenko from 40 meters altitude
The large block at upper right is about 5 meters across; the Philae landing gear intrudes into the upper right corner.

The star of the morning was ÇIVA. Bibring showed 6 ÇIVA images forming a 360-degree panorama around the lander.

ÇIVA's view around Philae

ESA / Rosetta / Philae / CIVA

ÇIVA's view around Philae
Philae has returned the first panoramic image from the surface of a comet. The view, captured by the CIVA-P imaging system, shows a 360° view around the point of final touchdown. Parts of Philae’s landing gear can be seen in some of the frames.

It's a little hard to understand what's going on in this photo, so I've stretched the contrast a bit and annotated it, and rotated it so that the horizon is level:

ÇIVA's view around Philae (annotated)

ESA / Rosetta / Philae / ÇIVA / annotated by Emily Lakdawalla

ÇIVA's view around Philae (annotated)

So the lander is clearly tilted, with one image showing only sky. The lander has three legs, one in "front" and two to the side rear. The rear right leg is "down" in the image, while the front and rear left legs are up. Taken together with the geometry of the horizon -- which curves more than 180 degrees around the lander -- and it appears that the lander may actually be in a hole. When I imagined this, I laughed, imagining a comet jet suddenly popping Philae out of the hole like a pea from a straw. Or maybe an exogorth is down there somewhere! But, to get more serious, being in a hole would explain why the solar panels are getting so small an amount of illumination, and may unfortunately doom the lander to the short life dictated by its battery power.

What happens from here? They're doing as much science as they can without making any mechanical motions. That means no MUPUS surface properties experiments, or use of the APXS, and no deliveries to the gas chromatograph mass spectrometers. There is discussion of possibly using some of these moving devices to attempt to pop the lander up off the comet again, to try to get it into a position where they could recharge the battery. But if they do that, it will be a last-ditch effort.

I have more to report but no more time to report it today. I'll be at ESOC for one more day, tomorrow, and I'll try to bring you another update then.

Read more: Rosetta and Philae, pretty pictures, pics of spacecraft in space, comets, mission status, comet Churyumov-Gerasimenko, pics of hardware on earth

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Emily Lakdawalla

Solar System Specialist for The Planetary Society
Read more articles by Emily Lakdawalla

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