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Phobos
Hungry4info
post Mar 5 2010, 06:54 PM
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How would that explain the closeness of the craters (Surely, the impactors would have spread out)? How would that explain the presence of the linear features all over Phobos? What about the lines that cross and curve?


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JohnVV
post Mar 5 2010, 09:33 PM
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Hungry4info

a late night thought

but i do think they are the result of tidal stress

[attachment=20947:12_13phobos1.png]
i have been working on something else and came across a "crater chain "
luna north pole but ...

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peter59
post Mar 6 2010, 01:34 PM
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Absolutly stunning images from orbit 6906 (21.05.2009)

2592 x 2248 pixels
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5184 x 4488 pixels
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1008 x 1018 pixels

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Phil Stooke
post Mar 6 2010, 01:44 PM
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"I thought there was a theory that the sets of parallel lines were caused by ejecta from impacts on Mars? "

There was - still is in some minds, but I've never felt it was very satisfactory. My preferred idea is that the grooves are the surface expression of jointing (families of intersecting fracture planes) in the interior, possibly caused by large impacts, though not necessarily Stickney (the south polar depression is probably a very old crater larger than Stickney). They might also be caused by pressure release after excavation from the interior of a parent body, and opened by later impacts. The porosity we now expect can be explained as caused by open jointing.

Phil


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peter59
post Mar 6 2010, 02:41 PM
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Another stunning images from orbit 6916 (23.05.2009)

5184 x 5040 pixels
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1008 x 1018 pixels
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peter59
post Mar 6 2010, 02:43 PM
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..... and from orbit 6926 (26.05.2009)

5184 x 2728 pixels
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1008 x 1018 pixels
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Hungry4info
post Mar 6 2010, 04:35 PM
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Wow, ESA just won a little more of my heart.


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Antdoghalo
post Mar 6 2010, 10:11 PM
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QUOTE (Hungry4info @ Mar 5 2010, 11:09 AM) *
John W,

What about tidal fracturing (with loose material filling the gaps, falling in a funnel-like pattern to produce the observed crater shapes) followed by reorienting of the moon by some mechanism, then continued tidal stress in a new orientation.

As for the two criss-crosing linear features in the image below, I have no idea.



The fracture hypothesis Could be more likly because Phobos IS a rubble pile and surely tidal force from Mars might along with the larger impacts have caused some of the spaces between the rocks to be filled in by small particles and like a sinkhole here in Florida the above rock then collapsed to fill in the new space vacated by the particles that filled in the cracks and formed the holes on its surface.
The recent flyby could have been to determine if this is true. blink.gif mars.gif


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djellison
post Mar 6 2010, 10:51 PM
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QUOTE (Hungry4info @ Mar 6 2010, 04:35 PM) *
Wow, ESA just won a little more of my heart.


Don't get too excited - these are all old images - May '09 mostly.
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Hungry4info
post Mar 6 2010, 11:04 PM
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Even so, they are new to me. smile.gif

Could the tidal fracture interpretation of the linear features on Phobos explain why some of the close lines are slightly curved and intersect each other? Or why the linear features are seen across the entire moon? I was browsing through the Phobos images I've so far downloaded over the years and came across this one. It hurt my confidence in the tidal fracture hypothesis.
Attached thumbnail(s)
Attached Image
 


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peter59
post Mar 7 2010, 06:17 AM
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QUOTE (djellison @ Mar 6 2010, 11:51 PM) *
Don't get too excited - these are all old images - May '09 mostly.

Photos taken at the end of May 2009 and published in February 2010. It's an absolute record for ESA. It is cause for excitement and enthusiasm.




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CAP-Team
post Mar 7 2010, 08:20 AM
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Looks like some large boulders rolled or bounced on the surface of Phobos, possibly disappearing in space afterwards
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bk_2
post Mar 9 2010, 01:48 AM
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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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Explorer1
post Mar 9 2010, 03:51 AM
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Would there even be any evidence on the Martian surface of rings? They'd have to be large enough to make it to the surface, and if the atmosphere was thicker in those days than there'd be no way of knowing.

We'll get new photos in a couple days anyway though.
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Shaka
post Mar 9 2010, 06:08 AM
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QUOTE (bk_2 @ Mar 8 2010, 03:48 PM) *
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. blink.gif

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! smile.gif


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