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Origin of Phobos and Deimos, Where did these guys come from?
Chmee
post Mar 25 2006, 02:49 PM
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So what is everyone's thoughts on the origin of Mars' moons Phobos and Deimos? They are a bit of a mystery.

Here are the different theories:

1. They formed along with Mars when it accreted out of the plantary nebula.

Pros: explains how both are in the same circular, equatorial orbit around Mars.
Cons: Seems a strange coincidence that we are around to witness Phobos in such a low orbit that it is about (in a couple million years) to crash out of orbit. Also this would be the only case in the solar system where such small "asteroid-like" moons formed around such a large body.


2. They were captured into orbit around Mars.

Pros: This would explain their similarity to asteroids out in the Belt.
Cons: The probability that they would be both be captured into circular and equatorial orbits is virtually zero. Also, there is no know mechanism for asteroids to be captured by such a small body like Mars (after all the moons didnít do perigee burns to brake them into orbit) wink.gif

3. They were once part of a larger moon that that broke up into several pieces. Phobos and Deimos are the last remnants of it.

Pros: This would explain how both moons have circular and equaltorial orbits (since they started from the same body). Theoretically, there would have been many more moons at one time, but they have crashed into Mars one by one, as Phobos is on course to do.

Cons: Phobos and Deimos do not appear to be very similar compositionally, which is strange if they came from the same moon. Of course it was large enough, the large proto-moon may have been differentiated.

4. The moons were formed from a large impact early in Mars history, perhaps from the impact that created the Hellas basin or the northern lowlands. This impact formed a small debris field around Mars which accreted into the moons.

Pros: Explains the circular orbits of the moons and Moons created from early gigantic impacts seems to be a re-occurring theme we see in the rest of the solar system (i.e. Earth's Moon and likely Pluto's moons)

Cons: While it explains the circular orbits, it does not explain how they are equatorial.


I believe the favored theory this decade is number 3, where a large body was present, but was broken up.

What is everyone's thoughts?
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Harkeppler
post Jul 1 2008, 10:56 PM
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smile.gif By spectra, both martian moons look quite different to Mars (and seemingly differnt to each other) and are definenitly not composed my martian mantle material.

They seem to be captured bodies, maybe carbon rich condrite material. Main-Belt-Asteroids, I suppose.

Interestingly, there are a lot of elliptical impact craters on Mars which could be explained as impacts with low velocity and very small inclination. Maybe, there have been more "moons" at all. There could be a mechanism of gravitational influence (Jupiter, Saturn) which leads to asteroid orbits near to Mars and caption after a while. smile.gif
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Adonis
post Jul 12 2008, 08:38 PM
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QUOTE (Harkeppler @ Jul 2 2008, 12:56 AM) *
Interestingly, there are a lot of elliptical impact craters on Mars which could be explained as impacts with low velocity and very small inclination. Maybe, there have been more "moons" at all. There could be a mechanism of gravitational influence (Jupiter, Saturn) which leads to asteroid orbits near to Mars and caption after a while. smile.gif


I think this is an interesting posibility, which could gain consistency if the elliptical impacts are more concentrated in the equator and with their major axis orientation also parallel to the equator, since this hipothesis assumes that all the ancient Mars satellites which formed those impacts were, as Phobos and Deimos are now, near equatorial orbit.

I haven't any info about the concentration zone (if any) and orientation of elliptical impact in Mars. Have someone any info about this?

Regards
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Posts in this topic
- Chmee   Origin of Phobos and Deimos   Mar 25 2006, 02:49 PM
- - djellison   I've always thought it was 2 that was the most...   Mar 25 2006, 04:11 PM
|- - BruceMoomaw   QUOTE (djellison @ Mar 25 2006, 04:11 PM)...   Mar 27 2006, 08:24 PM
- - Phil Stooke   Well... this is an interesting subject, but not on...   Mar 25 2006, 06:16 PM
- - AlexBlackwell   I'll stand by my post from December 29, 2005.   Mar 26 2006, 05:40 PM
- - AlexBlackwell   To keep this thread active, I've copied my abo...   Mar 26 2006, 09:25 PM
|- - nprev   QUOTE (AlexBlackwell @ Mar 26 2006, 01:25...   Mar 26 2006, 10:14 PM
- - AlexBlackwell   QUOTE (tasp @ Mar 26 2006, 07:05 PM) Wow....   Mar 26 2006, 09:40 PM
- - BruceMoomaw   In this connection, there's an extremely inter...   Mar 27 2006, 02:23 AM
|- - Bob Shaw   QUOTE (BruceMoomaw @ Mar 27 2006, 03:23 A...   Mar 27 2006, 12:17 PM
||- - antoniseb   I think that option 4 is a serious possibility, an...   Mar 27 2006, 03:58 PM
|- - AlexBlackwell   QUOTE (BruceMoomaw @ Mar 27 2006, 02:23 A...   Mar 27 2006, 08:31 PM
|- - Bob Shaw   QUOTE (AlexBlackwell @ Mar 27 2006, 09:31...   Mar 27 2006, 09:51 PM
|- - BruceMoomaw   QUOTE (AlexBlackwell @ Mar 27 2006, 08:31...   Mar 27 2006, 10:02 PM
|- - AlexBlackwell   QUOTE (BruceMoomaw @ Mar 27 2006, 10:02 P...   Mar 28 2006, 12:25 AM
- - edstrick   ...."Perhaps there *are* remnants in orbit ar...   Mar 28 2006, 08:59 AM
- - BruceMoomaw   The resolution of the searches with ground-based t...   Mar 28 2006, 07:58 PM
- - Harkeppler   By spectra, both martian moons look quite differen...   Jul 1 2008, 10:56 PM
|- - Adonis   QUOTE (Harkeppler @ Jul 2 2008, 12:56 AM)...   Jul 12 2008, 08:38 PM
- - SpaceListener   A possibility is that Phobos and Deimos are the re...   Jul 2 2008, 01:57 AM
- - tasp   Just brain storming here; Perhaps Phobos and Deim...   Jul 2 2008, 03:24 AM
- - tanjent   One thing has bothered me for some time about the ...   Jul 13 2008, 07:48 AM
- - dvandorn   I can, however, imagine an impactor large enough t...   Jul 13 2008, 06:19 PM
|- - JRehling   I don't see a hard dividing line between accre...   Jul 14 2008, 10:58 PM
- - Harkeppler   The elliptical craters on Mars are not really cent...   Jul 14 2008, 11:28 PM
- - edstrick   Peter Schultz <Brown univ, Deep Impact mission,...   Jul 15 2008, 11:08 AM
- - Marz   I thought this was an interesting blurb: perhaps ...   Nov 1 2008, 06:26 PM
- - Vultur   The concept of an ancient moon that broke up is ve...   Nov 3 2008, 01:58 AM
- - Ron Hobbs   Triton? I think there is a consensus that it was o...   Nov 3 2008, 04:19 AM
|- - silylene   Couldn't another mechanism be that Mars captur...   Nov 4 2008, 04:54 PM
- - PhilCo126   Phobos and Deimos ( Fear & Terror ): http://ww...   Dec 5 2008, 04:33 PM
- - MarcF   Martian moon Phobos may have formed by catastrophi...   Sep 23 2010, 01:27 PM
|- - lavaphile   While very interesting, this is not quite as concl...   Oct 1 2010, 09:02 PM
- - Phil Stooke   "The overall reflectivity of Phobos is much l...   Oct 1 2010, 09:19 PM
- - pjam   One of the quotes in the Science daily article is ...   Jul 6 2011, 05:37 PM
- - antipode   QUOTE "We detected for the first time a type ...   Jul 7 2011, 12:14 PM
|- - Gsnorgathon   QUOTE (antipode @ Jul 7 2011, 04:14 AM) S...   Jul 7 2011, 05:58 PM
- - Juramike   Aren't phyllosilicates also found on comets? ...   Jul 7 2011, 12:49 PM
|- - pjam   QUOTE (Juramike @ Jul 7 2011, 10:19 AM) A...   Jul 12 2011, 03:08 AM
- - ElkGroveDan   Phyllosilicates are very popular these days. Last...   Jul 7 2011, 02:58 PM
- - Mr Valiant   Obviously, don't know much, but yeah, I'm ...   Jul 13 2011, 07:55 AM
- - Chmee   I had a thought today about a possible method of e...   Mar 27 2013, 02:29 AM
- - tasp   Running time backwards we see Phobos spiraling bac...   Mar 27 2013, 04:19 AM
|- - Chmee   QUOTE (tasp @ Mar 27 2013, 12:19 AM) Runn...   Mar 27 2013, 05:46 PM
|- - djellison   QUOTE (Chmee @ Mar 27 2013, 09:46 AM) I w...   Mar 27 2013, 08:38 PM
- - dvandorn   The problem is that simply reversing the orbit dyn...   Mar 27 2013, 04:23 AM
- - Phil Stooke   The real problem here is that these kinds of orbit...   Mar 27 2013, 08:41 PM
- - Chmee   In the debate over the origin of Phobos and Deimos...   Apr 28 2013, 07:18 PM


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