APOD: Contrasting Terrains on Comet... (2014 Aug 19)

Comments and questions about the APOD on the main view screen.
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APOD: Contrasting Terrains on Comet... (2014 Aug 19)

Post by APOD Robot » Tue Aug 19, 2014 4:05 am

Image Contrasting Terrains on Comet Churyumov-Gerasimenko

Explanation: Where should Philae land? As ESA's robotic spacecraft Rosetta circles toward Comet 67P/ Churyumov-Gerasimenko, a decision must eventually be made as to where its mechanical lander should attempt to touch-down. Reaching the comet earlier this month, Rosetta is sending back detailed pictures of the comet's unusual nucleus from which a smooth landing site will be selected. Pictured above, near the image top, the head of the comet's nucleus shows rugged grooves, while near the image bottom, the body shows a patch-work of areas sometimes separated by jagged hills. Some of the patch-work areas apparent on both the head and body seem to have fields of relatively smooth terrain. In the connecting area called the neck, however, visible across the image center, a relatively large swath of light-colored smooth terrain appears, punctuated occasionally by large boulders. Rosetta is scheduled to release Philae toward the dark mountain-sized comet nucleus with an anticipated landing date in November.

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Re: APOD: Contrasting Terrains on Comet... (2014 Aug 19)

Post by Nitpicker » Tue Aug 19, 2014 4:24 am

In the absence of any other information, I'd go for the neck. Looks like the most stable place, force-wise, given the way the comet rotates.

Peter Smith

Re: APOD: Contrasting Terrains on Comet... (2014 Aug 19)

Post by Peter Smith » Tue Aug 19, 2014 8:12 am

According to New Scientist (http://www.newscientist.com/article/dn2 ... -duty.html) Rosetta is not so much circling the comet as triangling it.

alex_apod

Re: APOD: Contrasting Terrains on Comet... (2014 Aug 19)

Post by alex_apod » Tue Aug 19, 2014 8:14 am

It's amazing to notice that, even with a very low-gravity force field on this object, the small rocks lying down at the boundary between the two parts of the comet seem to be stable and are not ejected by the rapid rotation of the nucleus.

Alex

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Re: APOD: Contrasting Terrains on Comet... (2014 Aug 19)

Post by zbvhs » Tue Aug 19, 2014 10:02 am

Looks like layering on that one face. This thing had to have been part of something bigger. As for where to land, come in along the axis of rotation.
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Re: APOD: Contrasting Terrains on Comet... (2014 Aug 19)

Post by JanDeBoer » Tue Aug 19, 2014 11:07 am

C-G looks like two huge snow and rubble balls smashed together. The outside gets covered with dust (regolith). Near the contact point the dust slides down accumulating near the comets components common center of mass (near the contact point I suspect). The surfaces facing the center of mass form sort of a canyon.

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Re: APOD: Contrasting Terrains on Comet... (2014 Aug 19)

Post by BDanielMayfield » Tue Aug 19, 2014 11:56 am

Although the ragged terrain is the most interesting, caution would argue in favor of landing on a smooth area.
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Re: APOD: Contrasting Terrains on Comet... (2014 Aug 19)

Post by Jarod997 » Tue Aug 19, 2014 12:39 pm

Landing on the neck could be dangerous - who knows how well those "spheres" are held together. And when the harpoons and drills latch on to the surface, it could promote cracking and possibly separation. Granted that's a worst case scenario.

In other news - it would have been nice if we had a scale to go with that image. I'm not sure if I'm looking at rocks, boulders, or hill tops.

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Re: APOD: Contrasting Terrains on Comet... (2014 Aug 19)

Post by rstevenson » Tue Aug 19, 2014 1:08 pm

alex_apod wrote:It's amazing to notice that, even with a very low-gravity force field on this object, the small rocks lying down at the boundary between the two parts of the comet seem to be stable and are not ejected by the rapid rotation of the nucleus.
Jarod997 wrote:In other news - it would have been nice if we had a scale to go with that image. I'm not sure if I'm looking at rocks, boulders, or hill tops.
Those small rocks are the size of houses. The comet is about 4 km long.

Rob

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Re: APOD: Contrasting Terrains on Comet... (2014 Aug 19)

Post by Discostarbear » Tue Aug 19, 2014 1:33 pm

It looks like sedimentary rock formed on the upper sphere and then it eroded exposing the layering and filling in the neck with softer powdery material and boulders.

giezerclassic

Re: APOD: Contrasting Terrains on Comet... (2014 Aug 19)

Post by giezerclassic » Tue Aug 19, 2014 1:53 pm

Is there a consensus that the away sphere in the picture is sedimentary rock? If not, is there a way, with this satelite/probe, to confirm the type of rock?

Guest

Re: APOD: Contrasting Terrains on Comet... (2014 Aug 19)

Post by Guest » Tue Aug 19, 2014 2:17 pm

The 'look of rock' as the substrate makes me wonder a bit. I know the old theory that comets are 'dirty ice balls'. But what if this comet is an icy rock ball? When it rounds the sun, it discharges the surface water supply... Then routes out to deep interplanetary space where is cools way down... Then as it starts the journey back to the sun into regions of warmer interplanetary space, such warmer interplanetary 'moisture' condenses (or some other means of depositing it) on the surface creating a new batch of ice, starting the whole process again...

Yes, I know. I can hear you laughing. But there was a time when such laughter accompanied the suggestion that the world was round, and not flat...

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Re: APOD: Contrasting Terrains on Comet... (2014 Aug 19)

Post by Chris Peterson » Tue Aug 19, 2014 2:34 pm

alex_apod wrote:It's amazing to notice that, even with a very low-gravity force field on this object, the small rocks lying down at the boundary between the two parts of the comet seem to be stable and are not ejected by the rapid rotation of the nucleus.
A half-day rotation period for an object with a radius of a couple kilometers isn't rapid rotation.
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Re: APOD: Contrasting Terrains on Comet... (2014 Aug 19)

Post by Ron-Astro Pharmacist » Tue Aug 19, 2014 2:50 pm

If the small rocks are the size of houses then the spires near the bottom of the photograph are close to multi-storied buildings if I'm interpreting the length of the shadows correctly. It will be quite the task unraveling the geography of C-G. They may wish Philae had wheel instead of legs to help that process though I'm sure Rosetta will scope out the comet quite well.
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Re: APOD: Contrasting Terrains on Comet... (2014 Aug 19)

Post by geckzilla » Tue Aug 19, 2014 2:59 pm

Ron-Astro Pharmacist wrote:They may wish Philae had wheel instead of legs to help that process though I'm sure Rosetta will scope out the comet quite well.
If Philae had wheels it would likely roll right off the comet into space.
Just call me "geck" because "zilla" is like a last name.

autodoc

Re: APOD: Contrasting Terrains on Comet... (2014 Aug 19)

Post by autodoc » Tue Aug 19, 2014 4:08 pm

The comet needs to be towed in to a low earth orbit to supply a steady stream of meteorites for collectors

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Re: APOD: Contrasting Terrains on Comet... (2014 Aug 19)

Post by Ron-Astro Pharmacist » Tue Aug 19, 2014 5:06 pm

geckzilla wrote:
Ron-Astro Pharmacist wrote:They may wish Philae had wheel instead of legs to help that process though I'm sure Rosetta will scope out the comet quite well.
If Philae had wheels it would likely roll right off the comet into space.
You are right Geck. Spiderman would have a hard time navigating this terrain.
…and sticking to it. Come to think about it – Philae comes pretty close to that concept :?:
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Re: APOD: Contrasting Terrains on Comet... (2014 Aug 19)

Post by MarkBour » Tue Aug 19, 2014 5:44 pm

Ron-Astro Pharmacist wrote:
geckzilla wrote:
Ron-Astro Pharmacist wrote:They may wish Philae had wheel instead of legs to help that process though I'm sure Rosetta will scope out the comet quite well.
If Philae had wheels it would likely roll right off the comet into space.
You are right Geck. Spiderman would have a hard time navigating this terrain.
…and sticking to it. Come to think about it – Philae comes pretty close to that concept :?:
True. Looks like a good challenge. They did bring duct tape, right? :-)

Oh, and seriously, if they land successfully, is the plan for Rosetta and Philae to be sending data right through the comet's perihelion?
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Re: APOD: Contrasting Terrains on Comet... (2014 Aug 19)

Post by ta152h0 » Tue Aug 19, 2014 7:01 pm

Anywhere facing the Earth
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Re: APOD: Contrasting Terrains on Comet... (2014 Aug 19)

Post by bystander » Tue Aug 19, 2014 7:26 pm

MarkBour wrote: is the plan for Rosetta and Philae to be sending data right through the comet's perihelion?

Yes

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Re: APOD: Contrasting Terrains on Comet... (2014 Aug 19)

Post by ta152h0 » Tue Aug 19, 2014 9:39 pm

do you think the ice is going to gas and bypass the liquid state ?
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Re: APOD: Contrasting Terrains on Comet... (2014 Aug 19)

Post by LocalColor » Tue Aug 19, 2014 10:37 pm

The "layering" looks more like the way heat radiating off a dark building melts "fins" into a frozen pile of dirty snow (see it in our back yard every winter.)

What a wonderful photo!! Go Rosetta and Philae!

Diana

Re: APOD: Contrasting Terrains on Comet... (2014 Aug 19)

Post by Diana » Tue Aug 19, 2014 11:21 pm

Well, someone has to go there...

This comet has a skull face. Just above the Neck. Looking to the right. It even has teeth!

Tootles,
Diana

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Re: APOD: Contrasting Terrains on Comet... (2014 Aug 19)

Post by SouthEastAsia » Wed Aug 20, 2014 2:11 am

I'd go for landing in the center of that crater/wall-like structure in the lower-right image, on Comet's body. It might be best protected against the elements there, while also perhaps being able to study more about the interior of a circular wall on a Comet? Just my thoughts...

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Re: APOD: Contrasting Terrains on Comet... (2014 Aug 19)

Post by alter-ego » Wed Aug 20, 2014 3:37 am

SouthEastAsia wrote:I'd go for landing in the center of that crater/wall-like structure in the lower-right image, on Comet's body. It might be best protected against the elements there, while also perhaps being able to study more about the interior of a circular wall on a Comet? Just my thoughts...
The landing site will need to be in sunlight a significant amount of time due to the solar cells covering the lander, Philae. The red zones (100% sunlight) are apparently not favored, while the yellow and orange zones are. The green spots mark provisional landing sites. The blue zones are in permanent shadow. The nature of the lat/long coordinate system is discussed some in Emily Lakdawalla's post (comet's unusual nucleus link in the APOD description)
Click to play embedded YouTube video.
http://www.planetary.org/multimedia/spa ... hilae.html
http://earthsky.org/space/exploring-ros ... erasimenko
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