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Emily Lakdawalla • Sep 09, 2016

Rosetta end-of-mission update

The European Space Agency posted several articles this morning about the plans for the end of the Rosetta mission scheduled for September 30, just three weeks from now. On September 29, a rocket burn will essentially cancel out Rosetta's orbital motion around the comet, initiating a free fall from an altitude of 20 kilometers. The spacecraft will impact the comet at a speed of about 90 centimeters per second at 04:20 PDT / 07:20 EDT / 11:20 UTC / 13:20 CEST, give or take 20 minutes. Upon impact, the spacecraft will automatically "passivate," cutting the radio connection to Earth and ending the mission forever. (Why does the mission have to end? Read ESA's FAQ.)

Rosetta's end-of-mission trajectory
Rosetta's end-of-mission trajectory A simplified overview of Rosetta’s last week of maneuvers at Comet 67P/Churyumov–Gerasimenko (comet rotation is not considered). After 24 September the spacecraft will leave the flyover orbits and transfer towards an initial point of a 16 x 23 km orbit that will be used to prepare for the final descent. The collision course maneuver will take place in the evening of 29 September, initiating the descent from an altitude of about 20 km. The impact is expected to occur at 10:40 UTC (±20 minutes) at the comet which, taking into account the 40 minute signal travel time between Rosetta and Earth on 30 September, means the confirmation would be expected at mission control at 04:20 PDT / 11:20 UTC / 13:20 CEST (±20 minutes).Image: ESA

They have targeted a landing site in the Ma'at region on the "head" of the comet, in a flat area adjacent to a pit from which Rosetta has seen cometary activity. During the descent, they hope to observe at very high resolution the "goosebump" structures in the wall of the pit that they think may be a record of how the comet formed by accretion of smaller cometesimals. The team has named the pit Deir el-Medina for its resemblance to the Egyptian archeological site. Deir el-Medina is the site labeled "Ma'at_02" in the image below. Simulations of the landing suggest they should be able to touch down in that flat area between the sites marked "Ma'at_02" and "Ma'at_03" (within a region 500 by 700 meters in size).

Three Ma'at pits
Three Ma'at pits Pits Ma’at 1, 2 and 3 on Comet 67P/Churyumov–Gerasimenko show differences in appearance that may reflect their history of activity. While pits 1 and 2 are active, no activity has been observed from pit 3. The young, active pits are particularly steep-sided, whereas pits without any observed activity are shallower and seem to be filled with dust. Middle-aged pits tend to exhibit boulders on their floors from mass-wasting of the sides. The image was taken with the OSIRIS narrow-angle camera from a distance of 28 km from the comet surface on September 12, 2014. From left to right the pits measure 125 m, 130 m and 140 m across and are 65 m, 60 m and 50 m deep, respectively.Image: ESA / Rosetta / MPS for OSIRIS Team MPS / UPD / LAM / IAA / SSO / INTA / UPM / DASP / IDA

Here is a view of one of the Ma'at pits (I believe this is not Deir el-Medina, but rather the one named "Ma'at_01") showing the "goosebump" structures, which were also referred to as "dinosaur eggs" earlier in the mission. Here is a view of another comet pit in the Seth region, showing the "goosebump" structures, which were also referred to as "dinosaur eggs" earlier in the mission. (Thanks to commenter JB Vincent for pointing out that this was not a Ma'at pit.)

Dinosaur eggs or goosebumps in a comet pit
Dinosaur eggs or goosebumps in a comet pit Close-up of a curious surface texture nicknamed ‘goosebumps’. The characteristic scale of all the bumps seen on Comet 67P/Churyumov–Gerasimenko by the OSIRIS narrow-angle camera is approximately 3 m, extending over regions greater than 100 m. They are seen on very steep slopes and on exposed cliff faces, but their formation mechanism is yet to be explained.Image: ESA / Rosetta / DLR / MPS for OSIRIS Team MPS / UPD / LAM / IAA / SSO / INTA / UPM / DASP / IDA

Where exactly is this on the comet? I find it really difficult to orient myself on the double-lobed and craggy-shaped Churuymov-Gerasimenko, but the two deep Ma'at pits are actually relatively straightforward to find. First, look for an image of the comet in which it looks like a small animal (perhaps a capybara). The Ma'at pits are the dots on the left upper lip, maybe where whiskers would be rooted. (Or perhaps our space rodent has reptilian heat-sensing pits on its schnozz.)

If you consider the comet to be "upright" when looked at this way, the "three pits" image at the top of this post is "upside down." Thus oriented, I went through some of the Rosetta data archives and found a few views of the pits under different lighting conditions. Here's one that orients you to the comet and allows a peek at the floors of the pits.

Views of the Rosetta landing site (high sun)
Views of the Rosetta landing site (high sun) Two views of the prospective Rosetta landing site in the Ma'at region of comet Churyumov-Gerasimenko, taken with the wide-angle (right) and narrow-angle (left) OSIRIS cameras taken on August 30, 2014. The relatively high angle of the Sun allows a view into the bottoms of two prominent pits, each about 100 meters across, one of them shallower than the other. The shallower one has debris on its floor; this is Deir el-Medina. The planned landing site is to the upper left of Deir el-Medina in this view.Image: ESA / Rosetta / MPS for OSIRIS Team MPS / UPD / LAM / IAA / SSO / INTA / UPM / DASP / IDA / Emily Lakdawalla

In this view, the pit floors are shadowed, but the low lighting picks out interesting texture in the "flat" region in which Rosetta plans to land.

Views of the Rosetta landing site (low sun)
Views of the Rosetta landing site (low sun) Two views of the Rosetta landing site on the Ma'at region of comet Churyumov-Gerasimenko taken by the Navcam (left) and OSIRIS narrow-angle camera (right) on November 11, 2014. With the low sun angle, the interiors of the two prominent circular Ma'at pits are hidden, and a hint of texture can be seen in the smooth areas outside the two pits. The upper left pit is Deir el-Medina. The prospective landing site is to the let of Deir el-Medina in these images. The pits are about 100 meters across.Image: ESA / Rosetta / Navcam / MPS for OSIRIS Team MPS / UPD / LAM / IAA / SSO / INTA / UPM / DASP / IDA / Emily Lakdawalla

Finally, here's an oblique perspective, providing a better view of the textures on the walls of the pits.

Views of the Rosetta landing site onto pit walls
Views of the Rosetta landing site onto pit walls An OSIRIS wide-angle camera view of the head of comet Churyumov-Gerasimenko, with a perspective onto the interior walls of the two prominent pits of the Ma'at region. The most easily visible pit in this view is Deir el-Medina. The proposed landing site for Rosetta is to the lower left of Deir el-Medina in this view.Image: ESA / Rosetta / MPS for OSIRIS Team MPS / UPD / LAM / IAA / SSO / INTA / UPM / DASP / IDA / Emily Lakdawalla

I'm sure there are much better views in the archives. I pulled these from my own Rosetta image data pages, but the Rosetta mission has released much more data since I made those. If you find other great views of the landing site, please post them in the comments!

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