Phobos |
Phobos |
Guest_Sunspot_* |
Nov 11 2004, 11:46 PM
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#1
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Guests |
http://www.esa.int/SPECIALS/Mars_Express/
These images, taken by the High Resolution Stereo Camera (HRSC) on board ESA’s Mars Express spacecraft, are Europe’s highest-resolution pictures so far of the Martian moon Phobos. http://www.esa.int/SPECIALS/Mars_Express/SEM21TVJD1E_0.html |
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Mar 9 2010, 01:48 AM
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#2
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Junior Member Group: Members Posts: 22 Joined: 8-March 10 Member No.: 5252 |
Hi, I've been lurking here a while but at last I've been prompted to post.
The old images of Phobos set me thinking again about the grooves. I worried about them for months a few years back. Now I’ve had a new idea. The trouble with the ploughing through debris theory [John B Murray 2006] is that at orbital altitude there won’t be strings of ejecta narrow enough to make those regular grooves, it has to involve some fine ring material. But if Phobos was ever orbiting in a ring it would have the same velocity as the ring material in which it orbits, it wouldn't have ploughed through anything. So here’s the new idea. If, during the period when Mars had these putative rings, Phobos had a more elliptical orbit, but in the same plane as the rings, it would have come screaming in and ploughed right through the rings at periapsis on each orbit. To create the grooves, Phobos would have had to be tidally locked as it is now, to present the same face to the flak, though it must have wobbled a bit, going by the angles of the grooves. (cf. Murray) Perhaps the rings even formed in the same event that created Phobos, whether impact or capture, presuming there was enough material dislodged by the tidal disruption if it was the latter. I understand that the orbits of smaller particles and dust circularise and flatten out relatively quickly by collisions, while a large chunk like Phobos, would slowly circularise by tidal forces, so if they formed together there would be a time when the orbits were different. Another point is that a common source for Phobos and the rings would be most likely to put them in the same plane. The involvement of rings of fine material is crucial. How else could a groove form that extends the length of the flank in serene uniformity, than by collison with a narrow linear obstacle like a ring edge on? There are some less well defined grooves that are clearly crater chains, like the five little craters almost identical in size, equally spaced in a line parallel to one of the huge smooth trenches. These could have been caused by irregularities in the rings, bits where larger and fewer ring particles accumulate. Obviously the rings didn't persist for long, they aren't there now, and Phobos must have disrupted their structure by it's regular visits. But they lasted long enough to leave the grooves. Does it have any merit? |
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Mar 9 2010, 06:08 AM
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#3
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Senior Member Group: Members Posts: 1229 Joined: 24-December 05 From: The blue one in between the yellow and red ones. Member No.: 618 |
Does it have any merit? I'd have to say it tickles my fancy, but I don't know enough about orbital dynamics to pick out showstopper flaws. Certainly it strikes me as more in keeping with the overt appearance of the grooves, than mechanisms invoking tidal stresses or big impacts on Mars. What you do need to explain is the quite uniform width of particular grooves, together with the significant variations in width between grooves. The widest grooves are clearly chains of individual impact craters that overlap to a limited extent. Your hypothesis requires impacts with a family of objects of relatively large and uniform size. Small craters are not evident. The narrower grooves aren't so easily resolved into individual craters, but are presumably the result of numerous impacts with families of smaller objects; again quite uniform within grooves, but with negligible 'contamination' by the large objects forming the wide grooves. Somehow you have to postulate a size distribution of objects within your rings that either spatially or temporally sorts out size classes. I'll be hornswoggled if I can readily visualize that, but an orbital mechanics guru might be able to. It would be groovy if we could work out the sequence of deposition of the grooves. My first-glance WAG would be that the narrowest grooves deposited earlier than the widest, but I wouldn't bet my surfboard on it. Best of luck with your "ring-whacker" hypothesis! -------------------- My Grandpa goes to Mars every day and all I get are these lousy T-shirts!
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