[X] My Assistant

[nprev]

This pic from Oppy made me wonder about Phobos' & Deimos' visual aspects for a hypothetical surface observer using Mark I eyeballs. The image seems to show at least a faint lens flare on the right side from the main image; how bright are the moons from the surface? Also, are at least some surface features on Phobos like Stickney visible?

Probably old questions, probably old territory...but still interesting to contemplate from the rather unique viewpoint of the MERs.

[AndyG]

In terms of the brightness...


Baseline Phobos (observer at 70 deg north latitude, Mars at aphelion, Half Phase) = -7.6

Take away 0.4 for Mars at perihelion
Take away 0.8 for 0 deg (equatorial) viewers
Take away 0.8 for Full Phobos
Max brightness of Phobos = -9.6


Baseline Deimos (same conditions) = -4.3

Take away 0.4 for Mars at perihelion
Take away 0.3 for 0 deg (equatorial) viewers
Take away 0.7 for Full Deimos
Max brightness of Deimos = -5.7


(Give or take a tenth or so.)

Since Venus (max mag -4.4) can cast shadows, both moons also will throughout most of their phases.** Phobos, at best, is about 17 times dimmer than a full moon on Earth - that's still a lot of light for the human eye, but no chance of colour vision: Mars' cats will also look grey at night.

As to details, I can convince myself that the Moon's Mare Crisium is viewable without aid - but that's a dark maria over lighter rock. Phobos has less variety in albedo, and seen from Mars is around a third the apparent size of the Moon. However, I think it would be possible to see shadows in Stickney depending on the angle of illumination - there must be times when the near and far rims of that crater will catch sunlight, leaving a pool of black in between.

Andy

** I'd like a photo of the shadows of the pancam mast during a good full Phobos/Deimos night - just how unearthly would that look...

[djellison]

** I'd like a photo of the shadows of the pancam mast during a good full Phobos/Deimos night - just how unearthly would that look...

Problem is, it'd be fairly hard to see - and require an exposure long enough to probably smear such a shadow to a greater ammount than its own width

Doug