Origin of Phobos and Deimos, Where did these guys come from? |
Origin of Phobos and Deimos, Where did these guys come from? |
Mar 25 2006, 02:49 PM
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#1
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Member Group: Members Posts: 154 Joined: 17-March 05 Member No.: 206 |
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) 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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Mar 27 2013, 08:41 PM
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Solar System Cartographer Group: Members Posts: 10229 Joined: 5-April 05 From: Canada Member No.: 227 |
The real problem here is that these kinds of orbital extrapolations only work for limited periods. The system becomes chaotic especially near any resonances, and as Doug pointed out there could have been other short-lived chunks which would make it even more chaotic. Even now we can't predict precisely where the two moons will be from one decade to the next - the MSL Mastcam images on about sol 42 showed the moons a bit off where they were expected (there's an LPSC abstract on it somewhere). So we can't possibly extrapolate backwards very far.
Phil -------------------- ... because the Solar System ain't gonna map itself.
Also to be found posting similar content on https://mastodon.social/@PhilStooke Maps for download (free PDF: https://upload.wikimedia.org/wikipedia/comm...Cartography.pdf NOTE: everything created by me which I post on UMSF is considered to be in the public domain (NOT CC, public domain) |
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Apr 28 2013, 07:18 PM
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#3
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Member Group: Members Posts: 154 Joined: 17-March 05 Member No.: 206 |
In the debate over the origin of Phobos and Deimos, it looks like several recent papers have been published supporting the 'giant impactor' theory. Here are the abstracts to a couple very interesting papers on this subject:
"Are Phobos and Deimos the result of a giant impact?" - Robert A. Craddock Icarus Volume 211, Issue 2, February 2011, Pages 1150–1161 "On the formation of the martian moons from a circum-martian accretion disk" Pascal Rosenblatt Icarus Volume 221, Issue 2, November–December 2012, Pages 806–815 |
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Jun 10 2015, 09:44 AM
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#4
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Member Group: Members Posts: 817 Joined: 17-April 10 From: Kamakura, Japan Member No.: 5323 |
I am not too sure if this is to be called a follow-on to the demise of Nozomi.
Today's Asahi newspaper here in Japan talks about JAXA sending a sample return mission to one of the Martian satellites. What follows is my translation. JAXA reported to the Space Activities Commision on 9 June 2015 (yesterday) that they woud like to launch a sample return mission to one of the Martian satellites during the early part of 2020's. SAC accepted it. The proposal is based on JAXA's ISAS's judgement that given Hayabusa experience and the expected experience from the sample return mission proposed for 2019 from the Moon the sample return mission form a Martian satellite is within the capability of ISAS. This is part of the next 10 year's space programme agreed by the government in January this year that three medium sized projects will be conducted during the next 10 years. P |
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