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Thread: Rosetta and 67P/Churyumov-Gerasimenko

  1. #16
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    Rosetta is in its 18.6 km medium orbit now. Decision on whether to go to the planned 9.6 km low orbit should have been taken today, if GO then burn will be on wednesday.

    NAVCAM's snapping pictures at about 1.4m/px resolution*, including the one below of the intended landing site J for Philae:

    Attachment 38152
    (Large version here)

    Large parts of pics taken these days are shadowed, since Rosetta's orbit is matching the comet's terminator plane, i.e. the exact line between day and night on the surface. It will remain on this orbital plane since this way its solar panels can stay edge-on to the gas flow coming from the comet, thus minimizing degradation damage. Placing Rosetta e.g. "ahead" of the orbit, i.e. permanently on the dayside, would mean the panels' "back side" would constantly be pummeled by the comet's gas flows.

    Philae is actively conducting science by now, using its surface sampling and analysis instruments to analyze the comet's coma. The SD2 surface drilling/sampling system is currently used to inhale some of the dust cloud into one of its 26 ovens so once heated the resulting gasses can be analyzed by the PTOLEMY gas chromatograph.


    *- OSIRIS' narrow-angle camera should have around 0.4 m/px resolution at this distance. At the low 9.6 km orbit it would be around 0.2 m/px. MPG isn't releasing any OSIRIS pics lately though.

  2. #17
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    Very nice. Inserting a satellite around a comet/asteroid is a very impressive feat. Kudos to the ESA.

  3. #18
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    GO for low orbit.

    Go for 10 km! | Rosetta - ESA's comet chaser

    Interesting NAVCAM picture of the neck area:

    http://blogs.esa.int/rosetta/files/2...M_141002_D.jpg

  4. #19
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    This boulder on the surface of 67P/CG has received the nickname "Cheops":

    Attachment 38187

    Cheops is located in this field, roughly in the center:

    Attachment 38188

    Cheops has a diameter of around 45 meters. The boulders strewn in the center have been nicknamed "the pyramids" due to their distribution; Cheops as the largest of them got its nickname from the largest pyramid. The Egyptian naming scheme will be kept for other features of the comet. Cheops and the other boulders stand out not just by being physically distinct from their surrounding, but also because their surface is brighter than the surface of the comet.

    Resolution in the first picture above is 0.5m/pixel, which is roughly equivalent to what (far larger) military reconnaissance satellites can reliably get off of objects on Earth. Picture was taken from 28.5 km distance on September 19th. Second picture with the wider situation was taken on August 6th, taken from a distance of 130 km with a resolution of 2.4m/pixel.

    Rosetta will reach its 10-km low target orbit tomorrow.

  5. #20
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    PS: And ESA publishes another NAVCAM picture today, this one from the "side". Cheops in the center.

    Attachment 38190
    Full version: http://blogs.esa.int/rosetta/files/2...M_141008_A.jpg

    Cheops even looks pyramidic from this angle. Size of the rock is basically a one-sixth version of the real Cheops pyramid; height is about 25 meters. Also note surrounding features in pic. Picture taken on October 8th from 16.9 km at 1.25m/pixel resolution.

  6. #21
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    Looks wind swept.
    Chimo

  7. #22
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    Gravity can erode a rubble pile perfectly on its own given long enough timespans, i guess...

    PS to that NAVCAM pic: Distance from center of comet was 16.9 km. Distance to surface shown is about 15 km.

    The 9.6 km orbit Rosetta is now moving to should bring the probe to within 7 km of the surface. OSIRIS is calibrated to focus up to about 1 km minimum distance, and at 7 km should get a resolution of around 15cm/pixel. The OSIRIS pic of Cheops is a crop from a 250% enlarged version, giving competing scientists as little data from OSIRIS to work with as possible*. Hence also the fuzziness of that pic. The classified full version of that picture would be 2048x2048 pixels covering about 1000x1000 meters, probably a similar area as that shown in the crop from the side-shot NAVCAM pic. Just from the top, and at around 3 times the resolution...

    * standard procedure for the Max-Planck-Institute for Solar System Research, which has been wellknown for this practice - that people in other countries just don't get - for decades.

  8. #23
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    New picture by Philae's CIVA-P system of Rosetta with the comet in the background, this time from 16 km distance:

    Attachment 38255

    Compare to the same thing from further away, posted on the first page of the thread.

    ESA is running the "Lander Operational Readiness Review" today, i.e. fixing down the landing scenario. Will be released tomorrow.

  9. #24
    Senior Contributor SteveDaPirate's Avatar
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    Quote Originally Posted by Officer of Engineers View Post
    Looks wind swept.
    Solar wind perhaps?

  10. #25
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    Even at perihelion (closest point to sun) the comet is still about as far away from it as the Earth - a bit farther out actually. The maximum solar wind it experiences would be somewhat similar to near-Earth asteroids like e.g. Itokawa.

    Here's another picture of the "swept" surface, this one showing Landing Spot J, the primary landing zone for Philae, taken from 30 km by OSIRIS at 0.5m/pixel resolution:

    Attachment 38270
    ( large version: Space in Images - 2014 - 10 - Philae's primary landing site from 30 km )

    What the surface actually reminds me of somewhat are deposit fields from melted glaciers on Earth. That might actually be what you're seeing; solidified volatiles (ices) inside the comet sublimate (i.e. turns straight into gas, such as what happens with "dry ice" made of frozen dioxide), then find an easy primary escape point - where the jets erupt, for this comet that would apparently be mostly in fractures in the "neck" region - and their retreating and internal movement then shapes the surface. It's glacial shaping - just neither fluvial (shaped from melting) nor moraenic (shaped under solid). Dust and gravel mixed into the ice would mostly settle in place, possibly pushed around a bit from the miniscule gravity, sliding down each others surface and thus smoothing out the surface somewhat. Larger rocks would be "exposed" in situ, and may slide similarly - one example for that could be that "rockslide" patch in the background of the Cheops side picture.

    At the same time, this sublimation also provides "wind" in some places: At places where sublimated ices outgas through small vents, lighter surface material is pulled along away from the comet. "Jets" seem to form where multiple such outgassings overlap, forming a disc between their cones; some of the material would be thrown off the venting gasses here and "snow" down to settle in the surrounding region due to the comet's own miniscule gravity, some would be blown off into space by the jet, and some, probably heavier material, would rather randomly tumble to settle in the zone immediately below.

    These are rocky and silty deposits at Melaspina glacier like the ones i'm thinking of above:
    Attachment 38271

    The reason for it all: 67P/C-G experienced a change in its orbit around the sun when it came too close to Jupiter in 1959, which moved the perihelion of its orbit inward towards the sun - from 2.7 AU previously to 1.24 AU now. The comet therefore in the past 55 years - in the 8 perihelia following that encounter - was heated far more by the sun than it used to be previously. This might be why we are not seeing surface ices, but may be seeing an ice-shaped surface. The sublimation encountered in these perihelia is of rather significant volume; during the 2007 perihelion (the last one before the next occurs in early 2015) the rotation period of the comet changed from one rotation in 12.7 hours to one rotation in 12.4 hours, presumed to stem from torque as a result of sublimation of ices on the comet.


    As for the surface material, I wouldn't be surprised much if it looks somewhat like Itokawa up close. This one, of Itokawa, was taken by Hayabusa during landing there:

    Attachment 38269

    The white bars in the picture are each one meter long, as a scale.
    Last edited by kato; 15 Oct 14, at 18:22.

  11. #26
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    ESA, DLR (Germany), CNES (France) and AIS (Italy) are jointly running a naming contest for the landing site.

    Name Rosetta mission's landing site

    You can propose a name for the site (no names of people) and have to give a short description of up to 200 words / 1500 characters why you think the name is appropriate, with the winning entry to be selected by an ESA jury. The name will not be IAU-approved but used by ESA and its cooperation partners (i.e. NASA) to refer to the site in the future.

    Winner receives a grant to cover travel costs and up to two overnight stays to to attend the descent and landing live at the Rosetta/Philae control center at Darmstadt, Germany on November 12th (limited to 1000 Euro from within Europe, 1500 from US; minors the same again for an accompanying adult). Food not included, refreshments as part of the media events. You need to upfront the money and redeem it with receipts.

    Conditions are: minimum age 13; you need to be a citizen or permanent resident of an ESA or EU member state or the USA; proposals must be made in a European language. One entry per person. May not have won in a previous ESA competition with the same prize, may not work at ESA or a cooperating partner space agency - including contractors - or live with such a person.
    Deadline: Oct 22nd, 23:59 GMT.
    Last edited by kato; 16 Oct 14, at 17:57.

  12. #27
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    NAVCAM pictures from this wednesday have been released, from an orbit of 9.9 km, or 7.9-8.9 km to the surface of the comet.

    Full versions here: CometWatch at 10 km | Rosetta - ESA's comet chaser

    Basically, more rocks and spectacular cliffs with a sandy surface cover and small boulders both spread around singly as well as accumulated around some cliffs.

    I've also by now seen some people comparing the scenery to the glaciers with mixed in and covering volcanic ash and soot in Iceland, such as these.

    ESA has also published a comparison picture showing the comet both with their surface brightening and as seen in original side-by-side:

    Attachment 38299

    And as further comparison, the Earth, Jupiter's moon Enceladus, the Moon and 67P/C-G:

    Attachment 38300

  13. #28
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    Picture of Cheops taken from 7.9 km distance by NAVCAM, resolution is 67 cm/pixel:

    Attachment 38341
    (click picture for large version)

    Also note the region where the smooth ground transitions into rock in the upper right quarter of the picture. Looks more like multiple layers to me. And somewhat glacial too - see post above.

    Here's the section a bit further "right" on the comet (the pictures overlap), showing this layering in this transition zone - and beyond - even better:

    Attachment 38342
    (click picture for large version)

  14. #29
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    Rosetta has switched over to her pre-landing orbit - i.e. she's currently making her way back up to a 30 km target orbit (should reach it about next night). From this orbit, Rosetta will later on do a rapid burn towards the comet before detaching Philae (so it falls towards the comet) at 22.5 km distance and then move back into a proper orbit at about 20 km altitude.

    Less than 12 days left till Philae is going to touch down on the surface.

  15. #30
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    Following the naming contest mentioned above, the primary landing site J has been named "Agilkia".

    Agilkia is the name of the island in the Nile that ancient Egyptian complexes were evacuated to from the island of Philae (after which the lander is named) during the flooding in connection with building the Assuan Dam. The name had been suggested by 150 out of 8000 participants in the contest, the second-most-named entry was "Abydos" (at 149 entries).

    Agilkia was also imaged again by NAVCAM from 30 km altitude where Rosetta is at now in pre-delivery orbit:

    Attachment 38395
    (click picture for large version)

    To locate Agilkia in this picture: Roughly on the center line dividing the picture into an upper and lower half there is a prominent cliff-like depression with what looks like a small landslide in the center of the cliff. This is the same depression as in this picture, where the red circle gives the one-kilometer landing ellipse for Philae.

    Also, ESA is now releasing all NAVCAM images under Creative Commons license. This officially allows anyone to use or modify them including commercial use provided the source and license is given. Therefore:

    All NAVCAM images in this thread: ESA/Rosetta/NAVCAM, CC BY-SA IGO 3.0.
    Last edited by kato; 04 Nov 14, at 17:33.

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