POLL: Where did Phobos & Deimos come from?

[3488]

Where did the Mars moons Phobos 27 KM wide & Deimos 15 KM wide come from?

Any thoughts & why???

Please explain your choice.

A few images below of Phobos.

Phobos enhanced colour from MRO HiRISE.

Phobos crater appox 5 KM wide with large boulder. MRO HiRISE.

Phobos, material sliding down walls of Stickeny Crater. MGS MOC.

Phobos, antimars side. Mars Express.

Phobos, hills & craters on 5 KM wide horizon. Mars Express.

Phobos, looking down from 'above'. N marks North Pole on Phobos. Mars Express.

Proposed Phobos-Grunt landing area. Mars Express.

Phobos MGS MOC. Stickney Crater top left, with giant boulders.

Phobos, large boulder MGS MOC.

Below a few Deimos images.

Deimos. MRO HiRISE.

Deimos. MRO HiRISE. Looks almost like a boxing glove from this angle!!!!

Deimos Viking 2 orbiter. Viking 2 passed just 45 KM from Deimos when this was taken.

#

A few more Viking 2 orbiter images of Deimos.

Deimos south polar region. Viking 2. It was southern Summer in the Mars system at this time.

Andrew Brown.

 

[EarthlingX]

I can not decide on voting options, but i would like to comment on the lack of streaks on Deimos, which are very common on Phobos. Looks as if my attempt, to explain those streaks with the tidal forces, is in peril.

Deimos is, of course, much further out, and therefore under less tidal influence.

Wiki : Phobos (moon)
Phobos Semi-major axis = 9,377.2 km (5,826.7 mi)

Wiki : Deimos (moon)
Deimos Semi-major axis = 23,460 kilometres (14,580 mi)

As to the poll, i think the most unlikely option is, that they formed from the initial debris. Wouldn't their orbits degrade by now ?

 

[vogon13]

I think the curious striations on Phobos might be resultant from Phobos 'interacting' with materials organized rather similarly to the debris belts (I purposely do not refer to them as rings) around Rhea.

Additionally, I suspect for a very long periods of time (3 billion years, maybe longer), Phobos and Deimos were in a resonant condition (probably 3:1), and uniquely to themselves, they would have been the only resonant pair we know of in our solar system that had their resonance span the synchronous altitude for the object they orbited.

Not sure how one would mathematically model that situation (particularly with out extremely accurate data on the variations in the Martian gravity field (like our moon's masscons), and equally accurate data on Mars oblateness, and how the poles have wandered during that period.

 

[EarthlingX]

I think the curious striations on Phobos might be resultant from Phobos 'interacting' with materials organized rather similarly to the debris belts (I purposely do not refer to them as rings) around Rhea.

Yes, i like this thought. That track of a probably tidally crushed asteroid on a Phobos surface leads in this direction. It might be even related to the reddish surface cover, we see in this neighbourhood - Ceres also, i think.

Additionally, I suspect for a very long periods of time (3 billion years, maybe longer), Phobos and Deimos were in a resonant condition (probably 3:1), and uniquely to themselves, they would have been the only resonant pair we know of in our solar system that had their resonance span the synchronous altitude for the object they orbited.

What do you think happened ?

Wiki : Moons of Mars
They seam to be close to 1:4 now, Deimos leaving and Phobos falling :
(orbital data)

• Deimos - 1.262 44 d = 30.30 hours
• Phobos - 0.31891023 d = 7 h 39.2 min

Mars Sidereal rotation period = 1.025 957 day = 24.622 9 h

Moons :

The origin of the two moons is not well understood. Their low albedo and carbonaceous chondrite composition are similar to asteroids and capture remains the favoured theory. Phobos' unstable orbit would seem to point towards a relatively recent capture. But both have circular orbits, very near the equator, which is very unusual for captured objects and the required capture dynamics are complex. Accretion early in Mars' history is also plausible but does not account for the moons' composition resembling asteroids rather than Mars itself. A third possibility is the involvement of a third body or some kind of impact disruption.[108]

* [108] Geological History:Moons of Mars (Archived version)

and

Orbit and Inclination :

At one point 1.35 million Earth years ago, Mars had an eccentricity of roughly 0.002, much less than that of Earth today.[101]

* [101] http://main.chemistry.unina.it/~alvitag ... sDist.html

The third figure shows the variation of the eccentricity of Mars over the time span of 5.5 million years, centered at the present epoch. The integration took a total of four days on a 1700 Mhz machine. The figure shows that there has been a time, 1.35 millions years ago, when the orbit of Mars was nearly circular (e = 0.002).

and interesting search result :
* Solex :

Basically, SOLEX is a free computer program modelling the N-body dynamics of the Solar System, and it is the result of a long and patient amatorial work by the author (Aldo Vitagliano).
Its heart is a powerful numerical integrator, and the many additional functions make it a greatly flexible program, which at the same time is very simple to use and very powerful in its performances. It can just give aesthetic pleasure and help in identifying sky objects, or it can be used by an experienced researcher as a tool to investigate aspects of the solar system dynamics such impact probabilities and chaotic motion. More ...
Last but not least, the software package contains a companion orbit-determination program (EXORB), suitable for the determination of orbital elements of minor bodies (asteroids and comets) from their astrometric observations.

Not sure how one would mathematically model that situation (particularly with out extremely accurate data on the variations in the Martian gravity field (like our moon's masscons), and equally accurate data on Mars oblateness, and how the poles have wandered during that period.

A bit of background for me :
Wiki : Mass concentration (astronomy)

In astronomy or astrophysics mass concentration or mascon is a region of a planet or moon's crust that contains a large positive gravitational anomaly.

Is there no gravitational disturbance data from the orbiters ?

 

[vogon13]

Correction:

As you noted, I meant to say 4:1 instead of 3:1.

Also,
Perhaps the formation of Angelina Stickney crater is what disrupted the resonance . . .

 

[Shpaget]

Are we really going to decide on their origin with a poll? :lol:

 

[StarRider1701]

* Solex :

Basically, SOLEX is a free computer program modelling the N-body dynamics of the Solar System, and it is the result of a long and patient amatorial work by the author (Aldo Vitagliano).
Its heart is a powerful numerical integrator, and the many additional functions make it a greatly flexible program, which at the same time is very simple to use and very powerful in its performances. It can just give aesthetic pleasure and help in identifying sky objects, or it can be used by an experienced researcher as a tool to investigate aspects of the solar system dynamics such impact probabilities and chaotic motion.
Last but not least, the software package contains a companion orbit-determination program

Not sure how one would mathematically model that situation (particularly with out extremely accurate data on the variations in the Martian gravity field (like our moon's masscons), and equally accurate data on Mars oblateness, and how the poles have wandered during that period.

Is there no gravitational disturbance data from the orbiters ?

I agree with Vogon. While I'm sure that's a fine computer and all, I'm not sure how well it is able to predict such events so long ago given the actual data we currently have about the planet Mars. While I'm sure we think we know a lot, I'd be skeptical about those types of predictions regarding the orbital histroy of the Earth, a planet we know a heck of a lot more about!

 

[bdewoody]

My guess is that they are a couple of stray rocks from the asteroid belt.

 

[MeteorWayne]

An interesting paragraph from a review article in the March 19 Science by Cuzzi,et al, reviewing what we've learned about the rings of Sturn after 6 years of study by Cassini. (I'm only about halfway through the article, I find myself rereading paragraphs to grasp the concepts more fully, and gazing at the images then drifting off in awe... )

"Most of the moons that lie in or close to the rings--Pan to Pandora-- display appreciably nonspherical forms, surprisingly low densities (substantially smaller than the density of solid water ice), and shapes and sizes that approximately match those of their associated Roche Lobes, which suggest accretion of loose rubble onto a core substantially denser than the ambient ring material. This is reminiscent of numerical simulations of local aggregation of material in Saturn's rings and is apparent in the shapes of Phobos and Amalthea, close in moons of Mars and Jupiter."

This suggests to me that perhaps Phobos accreted in a debris ring after a major impact, possibly the one that created the topographic disparity between the northern and southern hemispheres.

 

[3488]

That is interesting Wayne.

Think I am up to posting now after a couple of days of not feeling too well (particularly Friday).

So Phobos according to the article formwed from a ring around Mars. Vogon also looked at that possibility with the link with the proposed debris belts around Saturn moon Rhea or evidence there of.

Also Phobos & Deimos look dissimilar. Phobos is the archetypal lumpy Potato shape, Deimos appears a lot more blocky & angular, particularly from the Mars facing side with only a few relatively large craters in proportion to much smaller ones. Also Phobos has a large number of large blocks & boulders, Deimos appears to have only much smaller boulders, not really any large ones that Phobos has.

Perhaps my final option no 4 looks more likely now given more thought.

The two are similar for sure, but there are some quite large differences.

Below a little seen view of Phobos from Mars Express in September 2008. Stickney Crater is clearly visible on the left.

A rarely seen Viking 2 orbiter image of Deimos, showing mostly the trailing Far Side of Deimos. Mars was only just off the frame to the left. The farside of Deimos has been very rarely seen in detail & IIRC this is the best view as yet. Unfortunately the sun angle was high, but the shape & surface features are visible, notably some small craters on the right & some rocky outcrops.

Andrew Brown.

 

[silylene]

Andrew, the farside looks suprisingly smooth. I know the sun's angle plays a role in this, but I suspect it is pretty smooth.

 

[EarthlingX]

How big would impact have to be, for debris to be able to form a moon, and what would that do to Mars rotation ? How does it relate to evidence ? Would both moons have to be formed at the same time ?

Surface of both moons can be covered with either asteroid or accretion dust, i'm not sure how much that proves ? I would suspect the same about meteorite impact counting ?

Impact craters might tell us something about trajectories of impacting material, right ?

 

[EarthlingX]

http://www.europlanet-eu.org : The Martian moon Phobos may have formed by catastrophic blast

Spatial locations of PFS observations of Phobos used for the compositional analysis.

Scientists now have firm indications that the Martian satellite Phobos formed relatively near its current location via re-accretion of material blasted into Mars’ orbit by some catastrophic event. Two independent approaches of compositional analyses of thermal infrared spectra, from ESA’s Mars Express and NASA’s Mars Global Surveyor missions, yield very similar conclusions. The re-accretion scenario is further strengthened by the measurements of Phobos’ high porosity from the Mars Radio Science Experiment (MaRS) on board Mars Express. These results will be presented by Dr. Giuranna and Dr. Rosenblatt at the European Planetary Science Congress in Rome, on Monday 20th September.

The origin of the Martian satellites Phobos and Deimos is a long standing puzzle. It has been proposed that both moons may be asteroids formed in the outer part of the main asteroid belt (between Mars and Jupiter) and were subsequently captured by Mars' gravity. Alternative scenarios suggested that both moons were formed in situ by the re-accretion of rocky-debris blasted into Mars’s orbit after a large impact or by re-accretion of remnants of a former moon which was destroyed by Mars’s tidal force. “Understanding the composition of the Martian moons is the key to constrain these formation theories”, says Dr. Giuranna of the Istituto Nazionale di Astrofisica in Rome, Italy.

Previous observations of Phobos at visible and near-infrared wavelengths have been interpreted to suggest the possible presence of carbonaceous chondritic meteorites, carbon-rich “ultra primitive” materials, commonly associated with asteroids dominant in the middle part of the asteroid belt. This finding would support the early asteroid capture scenario. However recent thermal infrared observations from the Mars Express Planetary Fourier Spectrometer, show poor agreement with any class of chondritic meteorite. They instead argue in favor of the in-situ scenarios.

“We detected for the first time a type of mineral called phyllosilicates on the surface of Phobos, particularly in the areas northeast of Stickney, its largest impact crater”, says Dr. Giuranna.

“This is very intriguing as it implies the interaction of silicate materials with liquid water on the parent body prior to incorporation into Phobos. Alternatively phyllosilicates may have formed in situ, but this would mean that Phobos required sufficient internal heating to enable liquid water to remain stable. More detailed mapping, in-situ measurements froma lander, or sample return would ideally help to settle this issue unambiguously,” he added.

...

 

[xXTheOneRavenXx]

This is some quite interesting stuff. I would have guessed that the Mars moons would have been captured objects from the asteroid belt. Just given their shape and density. With all the collisions in the asteroid belt that probably take place, I suspected these type of object could form quite easily. The largest impact on both of these object could be what sent them out of the asteroid belt to later be captured by Mars gravity.... or so I thought.

 

[MeteorWayne]

Capture is extremely difficult, expecially for a very small (masswise) object like Mars. It requires a VERY VERY low relative velocity, or a binary where one part is ejected and the other is left behind.

 

[xXTheOneRavenXx]

See, there's still a few unknowns. Exactly how dense are these moons? If asteroid belt objects, what was their velocity as they approached Mars's gravitational pull? If they formed in orbit around Mars was it the same processes that formed our moon? or something else? Though Mars dust can be see of their surface, is this suggesting they are made from Mars material due to an impact, blowing chunks of rock into orbit forming these moons, or did the Moons accret the dust that was blown off Mars during other impacts?

In the first pic of Phobos, is that just false color dust around Stickney crater? Kind of looks like frost, though I presume it's just false coloring. It's hard to distinguish in the other pics.

 

[EarthlingX]

From the article :

“The asteroid capture scenarios also have difficulties in explaining the current near-circular and near-equatorial orbit of both Martian moons”, says Dr Rosenblatt of the Royal Observatory of Belgium.

The MaRS team, led by Dr. Martin Pätzold of the Rheinisches Institut für Umweltforschungh an der Universität zu Köln, Germany, has used the frequency variations of the radio-link between the spacecraft and the Earth-based tracking stations, in order to precisely reconstruct the motion of the spacecraft when it is perturbed by the gravitational attraction of Phobos. From this the team was able to reduce Phobos’s mass. “We obtained the best measurement of its mass to date, with a precision of 0.3%”, relates Dr. Rosenblatt. Phobos’s volume past estimations were also improved thanks to the cameras onboard MEx. The MaRS team was thus able to derive the best-ever estimate of Phobos’ density as 1.86±0.02 g/cm3. “This number is significantly lower than the density of meteoritic material associated with asteroids. It implies a sponge-like structure with voids making up 25-45% in Phobos’ interior”, says Dr. Rosenblatt. “High porosity is required in order to absorb the energy of the large impact that generated Stickney crater without destroying the body”, confirms Dr. Giuranna. “In addition a highly porous interior of Phobos, as proposed by the MaRS team, supports the re-accretion formation scenarios”.

A highly porous asteroid would have probably not survived if captured by Mars. Alternatively, such a highly porous Phobos can result from the re-accretion of rocky-blocks in Mars’ orbit. During re-accretion, the largest blocks re-accrete first because of their larger mass, forming a core with large boulders. Then, the smaller debris re-accrete but do not fill the gaps left between the large blocks because of the low self-gravity of the small body in formation. Finally, a relatively smooth surface masks the space of voids inside the body, which then can only be indirectly detected. Thus, a highly porous interior of Phobos, as proposed by the MaRS team, supports the re-accretion formation scenarios.

They are not sure either, just more confident :

The origin of both Martian moons is not, however, definitively elucidated since the density alone cannot provide the true composition of their interior. The future Russian Phobos-Grunt mission (Phobos Sample Return), to be launched in 2011, will certainly contribute to our understanding regarding the origin of Phobos.

The full text has been submitted for publication to the Planetary and Space Science journal’s Special Issue on Comparative Planetology: Venus-Earth-Mars.
http://www.sciencedirect.com/science/journal/00320633

I have not voted yet, though No 4 poll option seems most probable.

 

[3488]

WOW what an article EarthlingX. :shock: :shock:

Phobos Density = 1.86 G/CM[super]3[/super].

That is pretty low, vertainly to me suggestive of loosely packed material with internal voids.

Asteroid 253 Mathilde, Asteroid 21 Lutetia, Jupiter moons Amalthea & Thebe & Saturn moon Hyperion all have either large deep craters & deep floored craters, suggestive of material being 'pushed' in like polystyrene, rahter than shattering the body.

It would be interesting to get such an exact density for Deimos. Deimos certainly appears very different, more 'blocky' & with generally smaller & shallower craters in proportion to the diameter of Deimos than many on Phobos.

Perhaps they are not siblings after all.

Andrew Brown.

 

[MeteorWayne]

Or Deimos could have just assembled from bigger blocks of material.

 

[ZenGalacticore]

Perhaps Phobos formed by accretion after a major Mars impactor (as said above), and Deimos was a captured asteroid (as said above).

Phobos looks like a lumpy potato, and Deimos looks like a smooth potato.

Seems like if either one of them were formed by impact debris, that maybe there'd be one or two more of them orbiting Mars. With different impactors hitting the planet at different trajectories through the eons, seems like that's plausible, since say, four roid moons might be in different orbits and never collide with each other, forming a larger moon.

 

[brandbll]

WOW what an article EarthlingX. :shock: :shock:

Phobos Density = 1.86 G/CM[super]3[/super].

That is pretty low, vertainly to me suggestive of loosely packed material with internal voids.

Asteroid 253 Mathilde, Asteroid 21 Lutetia, Jupiter moons Amalthea & Thebe & Saturn moon Hyperion all have either large deep craters & deep floored craters, suggestive of material being 'pushed' in like polystyrene, rahter than shattering the body.

It would be interesting to get such an exact density for Deimos. Deimos certainly appears very different, more 'blocky' & with generally smaller & shallower craters in proportion to the diameter of Deimos than many on Phobos.

Perhaps they are not siblings after all.

Andrew Brown.

I'm just going to throw this out there; if Phobos has such a low density, is there any chance a real strong eruption from Mons Olympus could have escaped the atmosphere and formed something like Phobos or at least ignited some sort of formation? It could atleast explain it's close proximity to Mars.

Like i said though, i'm jsut throwing something against the wall and seeing if it could stick...

 

[MeteorWayne]

Nope, it wouldn't stick. Orbits aren't made by altitude, they require sufficient "sideways" velocity.

 

[3488]

Phobos is orbiting Mars at approx 2.1 KMS / 7,560 KPH or 1.3 MPS / 4,680 MPH.

For Phobos to be a piece of solidified lava from Olympus Mons that would have to have been one heck of an eruption!! Also as Wayne said, motion needs to be sideways, just upwards would not achieve orbit.

Phobos too appears to be composed of the wrong type of material to be formed from lava.

Andrew Brown.

 

[marsbug]

The article linked by earthlingX mentions phyllosilicates found- a liquid water related type of mineral. If the moon acrreted from remanants of a giant impacts, how well would phyllosilicates have syrvived the huge blast, and accretion process? It can't have been gentle.

 

[MeteorWayne]

SDC story on Phobos results