APOD: Phobos 360 (2013 Dec 25)

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APOD: Phobos 360 (2013 Dec 25)

Postby APOD Robot » Wed Dec 25, 2013 5:06 am

Image Phobos 360

Explanation: What does the Martian moon Phobos look like? To better visualize this unusual object, images from ESA's Mars Express orbiter have been combined into a virtual rotation movie. The rotation is actually a digital illusion -- tidally-locked Phobos always keeps the same face toward its home planet, as does Earth's moon. The above video highlights Phobos' chunky shape and an unusually dark surface covered with craters and grooves. What lies beneath the surface is a topic of research since the moon is not dense enough to be filled with solid rock. Phobos is losing about of centimeter of altitude a year and is expected to break up and crash onto Mars within the next 50 million years. To better understand this unusual world, Mars Express is on course to make the closest flyby ever on Sunday.

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Re: APOD: Phobos 360 (2013 Dec 25)

Postby Ann » Wed Dec 25, 2013 6:08 am

Here comes another Christmas bauble, this time with a twist! The cosmic Christmas tree seems to be full of them.

Interesting video! And Merry Christmas, everybody!

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Re: APOD: Phobos 360 (2013 Dec 25)

Postby Boomer12k » Wed Dec 25, 2013 6:42 am

If you look at Comets...you see many of the similar features...I wonder if Phobos and smaller "moons" are also "captured comets".

Not all ice need be on the surface per se....said of some Comets, and termed more...."Icey Dirtballs", than "dirty snowballs"..."The surface of the nucleus is generally dry, dusty or rocky, suggesting that the ices are hidden beneath a surface crust several metres thick."

Thus a seeming astroidal object, maybe be a comet ONLY when it is close enough to the sun.

I wonder if Phobos is just a captured Asteroid, or such a Comet....


Merry Xmas....one and all,

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Re: APOD: Phobos 360 (2013 Dec 25)

Postby Night eyes » Wed Dec 25, 2013 8:56 am

Seasons greetings to all you commenters. Your wit and knowledge is is an added pleasure to the posted APOD nightly viewing that this insomniac entertains herself with.
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Re: APOD: Phobos 360 (2013 Dec 25)

Postby Boomer12k » Wed Dec 25, 2013 1:34 pm

Are those REINDEER TRACKS?????


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Re: APOD: Phobos 360 (2013 Dec 25)

Postby rstevenson » Wed Dec 25, 2013 2:57 pm

See also this APOD, which has been repeated a couple times since. Phobos is a very interesting little moon.

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Re: APOD: Phobos 360 (2013 Dec 25)

Postby Chris Peterson » Wed Dec 25, 2013 3:21 pm

APOD Robot wrote:The rotation is actually a digital illusion -- tidally-locked Phobos always keeps the same face toward its home planet, as does Earth's moon.

No, this is wrong, and perpetuates a misunderstanding about the nature of tidal locking. In fact, Phobos rotates with a period of 8 hours. With tidally locked bodies, the illusion is that they don't rotate.
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Re: APOD: Phobos 360 (2013 Dec 25)

Postby Coil_Smoke » Wed Dec 25, 2013 3:31 pm

Chris Peterson wrote:
APOD Robot wrote:The rotation is actually a digital illusion -- tidally-locked Phobos always keeps the same face toward its home planet, as does Earth's moon.

No, this is wrong, and perpetuates a misunderstanding about the nature of tidal locking. In fact, Phobos rotates with a period of 8 hours. With tidally locked bodies, the illusion is that they don't rotate.
A "tidally Locked" satellite rotates once every complete orbit. How this series of images was captured is a good question. Merry Christmas...C_S
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Re: APOD: Phobos 360 (2013 Dec 25)

Postby Chris Peterson » Wed Dec 25, 2013 3:44 pm

Coil_Smoke wrote:A "tidally Locked" satellite rotates once every complete orbit. How this series of images was captured is a good question.

Mars Express is in a highly eccentric orbit that takes it both inside and outside the orbit of Phobos. This has allowed it to collect still images of the entire surface of Phobos, which (I assume) have been digitally mapped onto a 3D model of the moon and rendered into this movie.
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Re: APOD: Phobos 360 (2013 Dec 25)

Postby Psnarf » Wed Dec 25, 2013 3:52 pm

Looks more like a captured asteroid than a moon.

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Re: APOD: Phobos 360 (2013 Dec 25)

Postby Chris Peterson » Wed Dec 25, 2013 4:02 pm

Psnarf wrote:Looks more like a captured asteroid than a moon.

Not impossible, but captures are rare and dynamically difficult. I prefer the theory that it was ejected from the Martian surface after a large impact. What we need is a piece of it; it is unfortunate that the Russian sample return mission failed.
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Re: APOD: Phobos 360 (2013 Dec 25)

Postby geckzilla » Wed Dec 25, 2013 6:08 pm

Just call me "geck" because "zilla" is like a last name.
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Re: APOD: Phobos 360 (2013 Dec 25)

Postby Ann » Wed Dec 25, 2013 7:33 pm

Phobos, Scratch and...

Click to play embedded YouTube video.


On a slightly more serious note, I, as a color commentator, find the dark color of Phobos interesting. What has caused it? The composition of this Martian moon? Or the exposure to very strong UV radiation from the Sun? Maybe a layer of dark dust, similar to what causes the strange coloring of Saturn's moon Iapetus?

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Last edited by Ann on Wed Dec 25, 2013 7:44 pm, edited 1 time in total.
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Re: APOD: Phobos 360 (2013 Dec 25)

Postby Chris Peterson » Wed Dec 25, 2013 7:44 pm

Ann wrote:On a slightly more serious note, I, as a color commentator, find the dark color of Phobos interesting. What has caused it? The composition of this Martian moon? Or its exposure to very strong UV radiation from the Sun?

It would be necessary to look at some of the work on the spectral characteristics of the Martian moons to understand this better, but airless bodies are subject to space weathering (of which UV exposure is just one component), and in general this results in a reduced albedo.
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Re: APOD: Phobos 360 (2013 Dec 25)

Postby ta152h0 » Wed Dec 25, 2013 8:05 pm

That potato looks like it got into an epic fist fight with something
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Re: APOD: Phobos 360 (2013 Dec 25)

Postby Beyond » Wed Dec 25, 2013 8:19 pm

Aw, the piggies in Ann's video don't move, here, or at youtube. Oh well, they make less mess that way. :lol2:
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Re: APOD: Phobos 360 (2013 Dec 25)

Postby Ann » Wed Dec 25, 2013 8:48 pm

Beyond wrote:Aw, the piggies in Ann's video don't move, here, or at youtube. Oh well, they make less mess that way. :lol2:


No they don't!! :(

At least they grunt.

Let's try another grunt, and a very scratchy one at that, shall we?

Click to play embedded YouTube video.


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Re: APOD: Phobos 360 (2013 Dec 25)

Postby Beyond » Wed Dec 25, 2013 9:53 pm

I think this one may be trying to be a dog. :lol2: It could also use a little combing between the ears. :yes:
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Re: APOD: Phobos 360 (2013 Dec 25)

Postby navarch » Wed Dec 25, 2013 10:58 pm

Perhaps the solar system's largest geode?
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Re: APOD: Phobos 360 (2013 Dec 25)

Postby Night eyes » Wed Dec 25, 2013 11:21 pm

A geode, what a beauty idea, let's hope so.
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