Phobos |
Phobos |
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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 11 2010, 08:49 PM
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#2
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Member Group: Members Posts: 646 Joined: 23-December 05 From: Forest of Dean Member No.: 617 |
Extremely interesting idea, bk_2! Even I can grasp it and visualise it without understanding orbital dynamics. Therefore I think it's elegant, minimal, and retrospectively obvious - all attractive properties. (Then again, I have a notorious tin ear... ) A few questions that occurred to me reading the very interesting discussion:
1. What would a ring/moon impact look like? I suspect it shouldn't be pictured as a series of point-events - multiple distinct impacts, releasing a burst of energy and creating a crater. Instead there'd be a continuous rain of impacting particles at any given point. (A curtain of dust raining down in a ruler-straight line... what an image!) How would the end-result of lots of small impacts in one spot compare to one big one, assuming the same (cough) aggregate mass for the particles as for the monolithic impactor? Does the outgoing ejecta interact with the incoming ring material? 2. How do the masses of the moons where groove-like structures have been observed compare to those of moons without grooves? Larger objects might have more energetic internal processes renewing the surface, or perhaps there's an upper bound to the gravity of moon. (Wouldn't stronger gravity fields mean the ring particle orbits would be rapidly disrupted?) I'm thinking of the wake images of the Saturnian shepherd moons and trying to visualise the dynamics with a larger shepherd, but I'm handicapped by ignorance of the calculus; and ISTR that these phenomena can be startlingly unintuitive!) 3. [EDIT: remove some of the foolishness.] 4. With respect to the crossing / intersecting angles of the grooves (and come to think of it, parallel grooves are presumably a special case of the general phenomena: something about the relative motion of ring and moon must have changed for the track to have moved across the moon's surface): - perhaps the groove-creation isn't continuous. Perhaps it was only one orbit of the moon in 100,000 intersects the ring. Or 1000 consecutive orbits, but with each episode happening only every 10^2, 10^3, 10^4 years. 6. Perhaps the groove-creation happened before Phobos was tidally locked? 7. Why are the grooves discrete structures, rather than very broad bands? If the moon/ring aspect angle was changing, presumably it would happen at a steady state. If every orbit the moon makes intersects with the ring, whilst it's rotational axis is slowly precessing (or it continuous slowly rotating prior to being tidally locked), that would make the impact zones broad strips, or the shape of two very thin triangles touching at the apex. Instead, we see distinct grooves of similar widths, separated by apparently virgin surface typical of any common or garden rubble-and-dust-pile. To me this suggests that either: i. whatever changes the location of the ring's intersection with the mooon was a sporadic, short-duration event; or, ii. that the actual ring/moon intersection that caused the rings 8. As I understand it, Saturn's rings are largely fine dust and ice grains - 10^-3cm -- 10^2 cm or thereabouts. The masses of particles in rings resulting from impacts on Mars, or from tidal disruption of passing rubble piles, might be expected to have a different mass distribution curve. 9-99: ..? -------------------- --
Viva software libre! |
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