Astronomy Picture of the Day 7-01-03

NASA ^ | 7-01-03 | Robert Nemiroff and Jerry Bonnell

[petuniasevan]

Astronomy Picture of the Day

Discover the cosmos! Each day a different image or photograph of our fascinating universe is featured, along with a brief explanation written by a professional astronomer.

2003 July 1

Martian Moon Phobos from MGS
Credit: Malin Space Science Systems, MGS, JPL, NASA

Explanation: Why is Phobos so dark? Phobos, the largest and innermost of two Martian moons, is the darkest moon in the entire Solar System. Its unusual orbit and color indicate that it may be a captured asteroid composed of a mixture of ice and dark rock. The above picture was captured recently by the robot spacecraft Mars Global Surveyor (MGS) orbiting Mars. Phobos is a heavily cratered and barren moon, with its largest crater located on the far side. From MGS images like this, Phobos has been determined to be covered by perhaps a meter of loose dust. Phobos orbits so close to Mars that from some places it would appear to rise and set twice a day, but from other places it would not be visible at all. Phobos' orbit around Mars is continually decaying -- it will likely break up with pieces crashing to the Martian surface in about 50 million years.

[petuniasevan]

Vital statistics for Phobos

Distance from center of Mars	9,378 km (5827 mi)
Distance from surface of Mars	5,989 km (3720 mi)
Radius	13.4×10.8×9.4 km (8.3x6.7x5.8 mi)
Mass	9.6 x 1015 kg (2.1 x 1016lbs)
Rotational Period	Synchronous
Orbital Period	0.3 days
Orbital Eccentricity	0.015
Orbital Inclination	1.0 degree

[petuniasevan]

[Graewoulf]

What comments do you know about that relate to the grooves on this moon? Is this a melting response?

[RightWhale]

If Phobos has ice, then all the more reason to put the first Mars base on Phobos. The manned descent to the surface of Mars can come later, there would be no hurry once a Phobos is set up.

[petuniasevan]

The grooves on Phobos are still a mystery. They may be related to the giant impact crater Stickney, as they are abundant there but are almost absent on the opposite side.

The European mission "Mars Express" is intended to images close-up the leading edge of Phobos when the craft arrives at Mars later this year.

Mars Global Surveyor image, 8-19-98.
Resolution is 12 meters.

Another theory is that the grooves are actually strings of craters formed from impact of materials thrown off Mars from meteoric impacts THERE. See the photo below and you may agree:

[DannyTN]

CAPTION THAT PIC

Unpurchased cheese builds up in France!"

[Michael Barnes]

Gracias for the bump...