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Adonis
Posted on: Mar 18 2010, 10:52 PM


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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.
  Forum: Mars Express & Beagle 2 · Post Preview: #157315 · Replies: 233 · Views: 146868

Adonis
Posted on: Mar 18 2010, 07:36 PM


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┐Is there any DTM model of Phobos available with more accuracy than the previous based on Viking data, based on the more accurate data from Mars Express imaging data, obtained in 2008 and from these recent fly-bys (and maybe from MRO data?.

If yes, ┐where I can find that info?

Thanks
  Forum: Mars Express & Beagle 2 · Post Preview: #157301 · Replies: 37 · Views: 65904

Adonis
Posted on: Feb 3 2010, 10:54 PM


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QUOTE (Den @ Feb 3 2010, 10:38 PM) *
Dust isn't only deposited - it is also blown off


I think you're correct,... and dust is also blown into (maybe more than blown off, because a crater acts like a hole in the soil). In any case, it's evident that older craters are more dust filled than newer ones. There are plenty of ancient dust filled craters almost completely filled, which rims are almost unrecognizable. Maybe it's complex to determine an approximate relationship of crater age from crater diameter and depth, but I suppose that's because it's not a trivial relationship, but I think it's evident that it exists. At least, this could be a method for chronological ordering crater ages in a same martian regional area, where sand and dust behavior are the sam in all their craters.
  Forum: Opportunity · Post Preview: #154961 · Replies: 409 · Views: 108259

Adonis
Posted on: Feb 3 2010, 09:10 PM


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I have some doubt related with crater's age estimation that I'd like to address, since I don't known if I could be right in something or wrong at all.

In the 6 years we have Opportunity in Mars we could have a close estimation of the of annual ammount of sand which falls into the martian soil from the atmosfere, due to the duststorms or suspension sand. This can be done from the visual appearance of the MER solar panels we have among those years from the cam images. Let's say this rate to be 0,1 mm per year (only a rough guess, maybe far from actual value I don't have, but suppose can be calculated with some accuracy). This dust is also, along the craters age, deposited in the craters floor, so craters in Mars gets filled with sand and their depth are, with time, been reduced. With that guessed rate (it's only an example), craters floor would be filled with 1 meter of sand every 10.000 years.

If we have the ratio of crater diameter versus crater depth for a new crater (something that I thing can also be done within a degree of accuracy), we can have a way to calculate craters age from the measured crater depth. Of course, some factor should be taken into account, due to the action of martian wind which both, gets sand into and send out sand from the crater. So, my question is ┐this method can be accurate enougth to calculate crater ages to some accuracy?

Thanks
  Forum: Opportunity · Post Preview: #154952 · Replies: 409 · Views: 108259

Adonis
Posted on: Nov 2 2009, 06:22 PM


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OK. I was wrong at all. Efectively, the image I mentioned was Hale crater, taken in 2007. One less science mystery for me rolleyes.gif and realized there's no recent HiRISE images sad.gif

Thanks Greg, imipak and Emily.
  Forum: Phoenix · Post Preview: #149025 · Replies: 142 · Views: 89424

Adonis
Posted on: Nov 2 2009, 12:58 AM


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QUOTE (Greg Hullender @ Oct 31 2009, 07:04 PM) *
MRO has been in Safe Mode since August 26, so it hasn't been taking many (any?) pictures.

http://marsprogram.jpl.nasa.gov/mro/newsro.../20090904a.html

--Greg



Thanks Greg.

But MRO web page have published HiRISE images taken in october 7th. So, if is still in safe mode, is capable of doing, at least, some (maybe selective) HiRISE images. And from that date (october 7th) MRO had some opportunities to image Phoenix landing site, which I understand is a science priority since we have there a known hardware to help us see the ammount of frozen ice laying there.
  Forum: Phoenix · Post Preview: #149002 · Replies: 142 · Views: 89424

Adonis
Posted on: Oct 31 2009, 05:21 PM


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MRO has almost a polar orbit. Thus, within the same approximate period of time, MRO is able to fly above, and spot, a given place in martian surface.

Phill got the Phoenix MRO images dated last July 30th and August 22th. This makes an approximate period of time of 23 days MRO should be able to fly above Phoenix landing site. Then, should I'm not wrong on this, next days counted in periods of 23 from August 22th were: September 12th and October 5th & 28th, in which theoretically MRO was able to spot Phoenix again..... except some of them it was night time when MRO was flying above Phoenix.

Then, ┐is it possible that some more recent MRO images of Phoenix landing site were still hidden inside the ammount of data sent by the orbiter? .... or I'm wrong in something I missed.

Thanks.
  Forum: Phoenix · Post Preview: #148932 · Replies: 142 · Views: 89424

Adonis
Posted on: Jun 2 2009, 11:18 PM


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I'd like to perform some basic calculations of aproximate elevations of some moonlets and waves above the ring plane. The problem is that the position of Cassini spacecraft relative to Saturn & Sun is needed, and that requires the hour of the day the individual Cassini images were shot. Info released along with Cassini images only comprise the day, but not the hour within the day. ┐is there any way to know the hour-of-the-day info of the moment a given image was shot by Cassini?
  Forum: Cassini general discussion and science results · Post Preview: #141334 · Replies: 200 · Views: 95031

Adonis
Posted on: Aug 6 2008, 08:41 PM


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Hi,

hope someone could help me. ┐where I can find downloadable DTM data for Phobos (if possible, the entire body)?

(DTM=Digital Terrain Data, that is, a file with numeric terrain elevation data)

Thanks in advance.
  Forum: Mars · Post Preview: #122901 · Replies: 1 · Views: 4441

Adonis
Posted on: 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
  Forum: Mars · Post Preview: #120525 · Replies: 61 · Views: 63172

Adonis
Posted on: May 31 2008, 04:05 PM


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Is anywhere information about the final landing chronology, specially the retro-phase ... I mean high versus time data?

Thanks
  Forum: Phoenix · Post Preview: #116456 · Replies: 166 · Views: 66429

Adonis
Posted on: May 29 2008, 06:58 PM


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QUOTE (ugordan @ May 28 2008, 08:19 PM) *
Indeed. I was also surprised how close to the heatshield Phoenix landed. Keep in mind that the heatshield was jettisoned some 12-ish km and the velocity was supposed to be about 45 degrees to vertical/horizontal. Several minutes later the lander lands less than 200 meters of it.


I got also surprised. I remember the same happened with both MERs: their heatshields got very close to the landers. There must be some reason for these so many cases. MER's heatshield and parachute design closely matches that of Phoenix. Perhaps the dynamic flight behavior of these heatshield when they're free from their landers are close to that of the parachute when hanging the lander.
  Forum: Phoenix · Post Preview: #116160 · Replies: 166 · Views: 66429

Adonis
Posted on: Apr 13 2008, 09:37 AM


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Hi everyone,

Images from MRO are fantastic. I'd like to share some especulations about some Phobos features.

The bright zone at the rim of Stickney coincide perfectly with the point in Phobos closer to Mars (or the central point as seen from Mars). At the same time, it's also the point with more tidal effect in Phobos or less gravity in the surface. I guess both facts (brightness and less gravity) should have some kind of relationship. Same happens with the opposite side, in which tidal effect is also maximized.

Because of tidal effect of Mars, close to this area gravity forces are not normal to the surface, but with a small inclination in direction to Mars, that is, some very small drag forces are in Phobos's surface in the direction to that bright zone. In the images I can see some dragged terrain or small attempts of avalanches in that direction (could it be this effect?).

In case of a big impact that shakes Phobos, the preference point to loose material into space should also be that point (could it be the reason for the bright zone?).

Grooves have also the direction and seems to converge to the maximal tidal effect zones. Because of the elongated aspect of Phobos, just before it got tidally locked to Mars there should have been a period in which it swung over the actual equilibrium point. In that period, those swings surely produced short time variations of drag forces in the surface due to tidal effects (could this be a reason for the grooves?).

Thanks





  Forum: MRO 2005 · Post Preview: #112221 · Replies: 52 · Views: 22399


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