Phobos Options

[JohnVV]

seeing as i already have a working folder for phobos and mro isis files
I would also need to install the lro isis files

And these things are BIG

[Phil Stooke]

http://www.esa.int/SPECIALS/Mars_Express/SEMK17CKP6G_0.html

Phil

[CAP-Team]

With the latest spice kernels for Mars Express I just simulated the Phobos flybys with Celestia, am I right that the Phobos-Mars Express geometry is almost the same for every flyby?
The flyby distances were pretty accurate.

[bk_2]

The ESA page says "Its origin is debated. It appears to share many surface characteristics with the class of ‘carbonaceous C-type’ asteroids, which suggests it might have been captured from this population. However, it is difficult to explain either the capture mechanism or the subsequent evolution of the orbit into the equatorial plane of Mars."

If it was a capture of a carbonaceous asteroid, possibly involving another body which was ejected in the process (which makes the capture hypothesis more plausible) could it not have shed a lot of matter by tidal disruption in passes below the Roche limit? The debris could have formed rings co-planar with the initially elliptical orbit of the main body.

If it was an impact, the impactor could have been a carbonaceous asteroid.

Although the ring-whacker idea has nothing to say about the evolution of Phobos' equatorial orbit, it must have been a factor in it's circularisation. Aerobreaking has been mentioned as a possible contributor. Ringbreaking would have been more effective than aerobreaking at transferring momentum, and would have occurred at a greater distance from the planet.

I wish there were a few more images on ESA page.

[alan]

The lumpy appearance of the lineations on Phobos remind me of the boulder trails inside Victoria crater. Could this be a possible explanation? Are they lined up in the right direction? I note that Phobos is inside the Roche limit for a strength-less object so the boulder would be lost due to tidal forces once they reached the inner or outer parts of Phobos, relative to Mars.

[Adonis]

Phobos grooves origin was an old thinking issue for me. I never believed about the explanation of being the result of crater ejecta sent to space from Mars impacts, because it would probably formed craters in Phobos rather than grooves.

I think Phobos is a captured asteroid. I know that a capturing mechanism is hard to explain unless an orbital energy loss of the captured asteroid should be introduced. Something like ours probes, which their retrorockets have to be operated in order to loss orbital energy to be captured by Mars instead of making a fly-by.

Phobos, as a prior free asteroid, had its own rotation. Now Phobos is tidally locked, so its rotation rate is equal to is orbital angular speed. Any moon tidally locked to its planet has some very know properties (Cassini laws):

- Its principal axis of inertia with minimal inertia is pointing directly to the center of mass of its mother planet.

- Other principal inertial axis is perpendicular to its orbital plane.

- The last principal inertial axis is orthogonal to the other two axes (in the direction of its velocity along the orbit).

There must be a time in which Phobos should have experienced tidal torques because of the non-alignment of its principal axis of inertia in the above mentioned way and because of its previous freely rotation rate before been captured were different from the tidally locked one. All this resulted in tidal torques applied to Phobos trying to force it to orientate its principal axis of inertia. This process generated internal energy inside Phobos and, also, differential tidal stresses in its ground and its interior.

The energy released in this process is the one that captured Phobos, circularized its orbit and tidally locked Phobos to Mars (and perhaps emanated volatiles along the grooves, forming what appear chains of craters).

At some point, as its rotation rate was decreasing, it should have experience a period of alternative torques (like a pendulum). All these effects generated dynamical differential tidal torques all along the moon (these stresses can be calculated, and I will do it when I´ll have enough spare time) which maybe can be the origin of the grooves. If the calculation of this mechanism predicts shear stresses in Phobos which alignments are consistent which the parallel pattern of the grooves, it will be a good theory for the origin of the grooves.

If this is a plausible mechanism, I guess it can explain some grooves evidences we see:

1. Why grooves are parallel and with origin in the closest point to Mars?, because are the lines of higher shear stress when Phobos was still in the process of been tidally locked to Mars. They converge in the point of the principal axis of inertia, which is the closes point to Mars, close to a point of the summit wall of Stickney crater.

2. Why are different families of grooves with small angle between them?, because Phobos could have had a small variation in internal density (is very porous) or because an impact, that change a little the orientation of its principal inertial axis.

3. Why Phobos has grooves crossing in almost right angle?, because in the past the principal inertial axis could be one orthogonal to the real now.

4. Why grooves cross almost all of the craters?, because craters were formed in Phobos when it was a free asteroid and grooves were formed later, in the process of beeing captured by Mars.

This is only a theory of mine (maybe I can be totally wrong), that I worked out a little, but still not enough to have minimal results.

Thanks. Hope explanation is easily understood.

[charborob]

The Mars Express blog has a post about the grooves of Phobos and their possible origin: http://webservices.esa.int/blog/blog/7. At the bottom of the post, there is a link to an article on the subject.

[Ian R]

Here's a cross-eyed stereo version of the red-blue anaglyph released by ESA:



http://webservices.esa.int/blog/post/7/1073

This post has been edited by Ian R: Apr 1 2010, 05:51 PM

[charborob]

Looking at the images cross-eyed produces inverted relief. You need to swap the images for correct cross-eyed viewing.

[Ian R]

Thanks for the heads-up charbobob! I've adjusted the image and replaced the incorrect version in my previous post.

[peter59]

ESA's Planetary Science Archive (PSA) - Mars Express new batch (2010-06-01). Orbits 7105-7697.
Nothing particularly exciting except Phobos and Deimos mutual event.

[Astro0]

A quick amination of that sequence.


EDIT: A second version.

[peter59]

Phobos thirty-eight years later. I'm not sure why the image taken by Mariner was published with a strange characteristic texture. I love this picture, it was with me all my life.
H6916_0000_S12

Below:
all the elements of surfaces recognizable on both images have been marked by arrows.

[brellis]

Q: Phobos is tidally locked; as Mars' North pole and rotation shift over the course of millenia, so will Phobos' orbit?

[Hungry4info]

A: No.

Tidal lock has driven the rotation axis to be parallel to the orbital axis (and Phobos' long axis to point to Mars). This is irrespective of Mars' rotation axis orientation. Tidal locks will force obliquity to either 0 (north pole "up") or π (north pole "down").

Edit: Another thing of note: If Mars' obliquity caused meaningful changes to the inclination of the orbits of Phobos, Deimos, then it would be no mystery as far as their origins are concerned as to why their orbits are coplanar.

Attached thumbnail(s)