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Was just reading about this on Discover magazine as the Mars Express Probe just released a closeup photo of the martian moon Phobos. Looks like a giant asteroid.
Was just reading about this on Discover magazine as the Mars Express Probe just released a closeup photo of the martian moon Phobos. Looks like a giant asteroid.
They were photographing a potential landing site for the Russian Fobos-Grunt mission.
The surface looks like a soft surface does when you brush along it with a coarse bristled paintbrush. The current thought seems to be that explosions on Mars created those striations, and that the material seems to be similar to the surface material of Mars than an asteroid. I think those are uncreative observations.
I would like to propose a possible different scenario. I think the core of Phobos could be a captured comet. The lines of craters then would not be impact craters, but lines of sinkholes formed when the subsurface material outgassed and left pockets which collapsed.
The striations formed by the lines of craters have much more in common with the lines formed in sedimentary rocks and slow accretions than those created by catastrophic impacts. Note the relatively consistent size of the cratering along each line, even as the line goes around the curves of the moon. Importantly, there is no "shadow" effect as would be seen if the moon was impacted from a blast in one direction. You can see the lines of craters even march across some of the larger craters. That is totally consistent with a larger impact blowing away the surface and gasses still outgassing from the striations themselves even after such impacts.
The reason that the surface resembles the material in Mars is likely because impacts on the surface of Mars threw debris high enough to make the larger craters AND deposit a relatively thin crust of Mars material on Phobos.
Initial comet formation itself is intriguing to me. I could speculate that a planetesimal out beyond Pluto got whacked in an impact and turned into some of the cometary bodies.
Consistent with the comet capture idea is the retrograde and extremely fast orbit of Phobos, unlike those of other moons.
So I'm a polymath. Sue me.
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