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Origin of Phobos and Deimos, Where did these guys come from?
edstrick
post Mar 28 2006, 08:59 AM
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...."Perhaps there *are* remnants in orbit around Mars!"....

Anybody looking for Black Monoliths?
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Guest_BruceMoomaw_*
post Mar 28 2006, 07:58 PM
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The resolution of the searches with ground-based telescopes has gotten almost good enough to detect Black Monoliths. If there are any additional moons of Mars, they are very small.

One other extremely half-baked idea -- I have no idea whether it would even work in physical terms. There is speculation now that Mars underwent major polar wander when its Tharsis Bulge formed -- that is, that the Bulge may have formed at a higher latitude, and that centrifugal "force" then caused the entire planet to tilt until the Bulge was at its equator. If Phobos and Deimos were originally in inclined orbits around Mars, could the gravitational field of the migrating Bulge have gradually dragged them along into their current equatorial orbits? Or am I spouting scientifically illiterate hooey?
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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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SpaceListener
post Jul 2 2008, 01:57 AM
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A possibility is that Phobos and Deimos are the remainders of a captured asteroid which had hit on the Mar's North Pole (Vastitas Borelis).
Does anyone believe that the returned samples by Phobos & Grunt spacecraft will be able to reveal this mystery?
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tasp
post Jul 2 2008, 03:24 AM
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Just brain storming here;

Perhaps Phobos and Deimos are primordial to Mars (or nearly so) but their 'original' orbits or an early evolved form of those orbits might have been something we don't see else where in the solar system today.

(Phobos or Deimos may or may not be remainders of a past 'population' of Martian satellites, I am not qualified to rate the effect that would have on this scenario's probability)

What I am thinking is fairly soon after Mars ( and the rest of the solar system 'settled down" after the late heavy bombardment) Phobos and Deimos might have had their orbits evolve into a resonant condition. But with a 'twist' we haven't seen anywhere else. The resonance was achieved with Deimos outside of the aerosynchronous orbit and Phobos inside.

Has anyone ever modeled a resonance that straddles the 'object/rotation/synchronous altitude ??

I guess I would not be surprised if there is 'sumthin' weird' about a resonant relationship like that, perhaps in allowing (presumably) short lived objects like Phobos and Deimos to persist into our epoch.

Why don't we perceive a resonant relationship now?

Maybe the Stickney impactor deceled Phobos sufficiently to break the resonance in the past <1gy, and we now observe it in a secularly accelerating orbit.

I don't have the mental faculties right now to see if Phobos is just inside a 3:1 (or whatever to 1) with Deimos, and the plausible decel from a Stickney impact would make up the difference . . . .

(but if someone else wants to, no problemo)


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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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tanjent
post Jul 13 2008, 07:48 AM
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One thing has bothered me for some time about the impact origin theory of moon formation. If a bunch of pieces get thrown into space by the impact, and then later coalesce to form a moon, the orbital momentum of the new moon should be equal to the net angular momentum, with respect to the parent body, of its component pieces of ejecta. It follows that moons can only result from glancing blows, because a symmetric 360 degree spray of debris resulting from a head-on vertical hit can never come together to form an orbiting body, even if some fraction crashes back into the parent body and some other fraction escapes entirely. Tiny close-in moons like the ones around Mars - that I can believe, because maybe they represent only a small fraction of the debris created by a large glancing impact. But big moons like our Luna?

Given a handful of parameters: size of the parent, size of the impactor, their densities, rotational speeds, relative velocity and angle of impact, it should be possible to project the portion of debris that will be too slow to escape and too fast to crash back, and then calculate their net angular momentum. I certainly couldn't do the calculation myself, but it must have been done by someone during the general discussion of moon formation. Whether by calculation or simulation, I would like to know what constraints the basic physics of collisions places on the size of the residual net momentum, and under what circumstances it is really possible to form moons that way. If so, it should then be possible to do the calculation backwards for any known moon, and establish the boundaries of the possible parameter values that could have brought it about. Some people here must know the literature well enough to point out where this has been done.

In the case of the Martian moons, of course, even if you can prove that such small close-in moons could come together from collision debris, they would likely be rubble piles, so the "Stickney objection" would still cause problems.
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dvandorn
post Jul 13 2008, 06:19 PM
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I can, however, imagine an impactor large enough to succumb to tidal break-up as it approaches Mars.

Bring a body the size of one of the larger asteroids across Mars just within the Roche limit. As the body breaks up, the release of the outer pieces would fling them into escape velocities, and breakup dynamics would allow some pieces to fall into stable orbits. The rest of the body would, of course, impact Mars.

In such a break-up scenario, I can well imagine pieces the size of Deimos and Phobos coming out of the process as relatively intact chunks of rock. Collisions with other pieces of the original parent body during the break-up would knock off the roughest edges, and accretion of smaller chunks over the months and years after the break-up would provide craters and regolith.

Perhaps Phobos looks like it has stretch marks because it was literally stretched in the process of the break-up on the original body? Subsequent mantling and alteration has not been enough to wipe the striations off the face of the little moon, since the cracking also controls impact-shock faulting and reinforces the surface expression of the cracks.

On a gestalt level, it hangs together... at least, for me.

-the other Doug


--------------------
“The trouble ain't that there is too many fools, but that the lightning ain't distributed right.” -Mark Twain
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JRehling
post Jul 14 2008, 10:58 PM
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I don't see a hard dividing line between accretion and impact. Mars was created by many impacts of bodies together. There wouldn't have been any special moment when God clicked a stopwatch and said "DONE!" and thereafter all impacts were impacts, whereas the day before they would have been accretion.

If material were being lofted skywards from Mars, we would see different possibilities as Mars evolved. But the new material being introduced by the impactor would be equally new to the Mars system whether it was this year or 4.5 GYA. And how much of the putative satellite was martian vs. foreign would also be on a continuum.
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Harkeppler
post Jul 14 2008, 11:28 PM
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The elliptical craters on Mars are not really centered on a special strip or plane. I assume that Mars was forced to a polar axis shift over the billenia and to an more or less erratic shift of the whole crust relative to the core. The latter can be explained as an effect of large mantle plumes and it may not have any astronomical reason.

It would be very interesting to get core sampels of Phobos and Deimos and some similar asteroids...

These funny moonx circling very near to the planet and phobos cruising faster that Mars rotates are extremly interesting. It is often said that Phobos will fall down on Mars in some millenia, but there is no complete mathematical theory of the tides in combination with the sun. Maybe Phobos will survive.

Harkeppler


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edstrick
post Jul 15 2008, 11:08 AM
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Peter Schultz <Brown univ, Deep Impact mission, etc> proposed some 20 years ago that the oblique impact craters form distinct populations at different inclinations and probably represent the traces of paleo-equators and provide evidence for polar wander on Mars. He proposes an original some 100 km <I think> moon that got shattered or tidally disrupted, Phobos and perhaps deimos are the last survivals.
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Marz
post Nov 1 2008, 06:26 PM
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I thought this was an interesting blurb: perhaps there were once three moons of Mars!

http://news.softpedia.com/news/Mars-039-Sc...oon-96469.shtml
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Vultur
post Nov 3 2008, 01:58 AM
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The concept of an ancient moon that broke up is very interesting.

It does seem very strange that Phobos is going to hit Mars in a relatively short (compared to the age of the solar system) time frame. It does seem to imply it may not always have been there. Are there any other bodies like that in the Solar System?
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Ron Hobbs
post Nov 3 2008, 04:19 AM
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Triton? I think there is a consensus that it was once the largest known TNO.

(136108) Haumea and its two moons look like they were formed fairly recently.

Phoebe and all of the retrograde moons of the outer planets.
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silylene
post Nov 4 2008, 04:54 PM
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Couldn't another mechanism be that Mars captured a binary asteroid system? From what I recall, there are some three-body solutions (in other interacting systems) which can result in dual capture if the parameters are just right. Have there been any attempts to model the Phobos / Diemos / Mars system with this scenario?

(negatives on this proposal would be that Phobos and Diemos aare non-identical in composition, whereas they may have been expected to be more similar if they were a binary system, and likely that this scenario involves some very exacting starting assumptions.)
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