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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 didn’t 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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Guest_BruceMoomaw_*
post Mar 27 2006, 02:23 AM
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In this connection, there's an extremely interesting new LPSC abstract ( http://www.lpi.usra.edu/meetings/lpsc2006/pdf/2195.pdf ) claiming that Mars Express' new full-surface photography of Phobos has solved the problem of the surface grooves -- which are definitely NOT cracks or ejecta trails from Stickney, but ejecta trails from several giant impacts on Mars itself that tossed debris upward to hit Phobos in various places! If so, then the idea that Phobos and Deimos themselves are composed of accreted debris tossed into Mars orbit by really giant impacts becomes more plausible.

Also, there's one tantalizing new EGU abstract ( http://www.cosis.net/abstracts/EGU06/05330/EGU06-J-05330.pdf ) announcing that the results of the first MARSIS examination of Phobos (from only 239 km distance) will be revealed at the EGU meeting. They got very high-quality data, but there's not a hint given as to what it will show.

QUOTE (Chmee @ Mar 25 2006, 02:49 PM) *
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.


Actually, I think it would mesh very well with equatorial orbits for them. If the debris from the impacts was originally tossed into inclined orbits (as it certainly would be), the orbits of the different pieces of debris would precess around the planet relative to each other -- so the paths of the various debris pieces would then cross at the equator, which is where collision would be most likely. There would then be exactly the same kind of process that gradually flattened out Saturn's rings into a near-perfect plane around its equator -- the difference being that Mars' equatorial ring of debris, being beyond the planet's Roche limit, would then continue accreting into a couple of lumps. In fact, this theory is the only one that explains really well why their orbits are so close to the equator.
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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
|- - pandaneko   I am not too sure if this is to be called a follow...   Jun 10 2015, 09:44 AM
- - scalbers   This will be among the topics covered in this dedi...   Sep 11 2015, 04:50 PM
- - Explorer1   http://www.nasa.gov/feature/goddard/phobos-is-fall...   Nov 11 2015, 03:34 AM
- - Phil Stooke   Not really, we just have another suggested explana...   Nov 11 2015, 04:23 AM
- - Chmee   New paper out in Scientific American that lends we...   Jul 5 2016, 04:13 PM
- - serpens   There are sufficient craters on Mars large enough...   Jul 6 2016, 05:49 AM
- - nprev   Tidal locking itself is not too surprising, esp. i...   Jul 6 2016, 06:04 AM
|- - ngunn   QUOTE (nprev @ Jul 6 2016, 07:04 AM) Cons...   Jul 6 2016, 08:20 PM
- - Phil Stooke   " I wonder if Phobos' orbital history can...   Jul 6 2016, 03:42 PM
|- - serpens   QUOTE (Phil Stooke @ Jul 6 2016, 04:42 PM...   Jul 6 2016, 11:28 PM
- - Floyd   You all seem to have missed a very recent paper: ...   Jul 6 2016, 08:49 PM
- - dvandorn   If the Nature Geoscience article is accurate, then...   Jul 6 2016, 11:42 PM
- - serpens   I remember as a youngster in the 1950s, being taug...   Jul 7 2016, 03:17 AM
- - Explorer1   Or we get a nice sample return from Phobos and Dei...   Jul 7 2016, 03:22 AM


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