Phobos orbits Mars eastward with a shorter period than Mars takes to rotate on its axis (also eastward). As a consequence Phobos is:
A)ahead of the tidal bulge it raises on Mars, so that Phobos is slowly drifting away from Mars.
B)ahead of the tidal bulge it raises on Mars, so that Phobos is slowly drifting toward Mars.
C)behind the tidal bulge it raises on Mars, so that Phobos is slowly drifting away from Mars.
D)behind the tidal bulge it raises on Mars, so that Phobos is slowly drifting toward Mars.

Question

Quizplus · Accepted Answer

Phobos orbits Mars faster than Mars rotates, causing it to be ahead of the tidal bulge it raises on Mars. This interaction results in a transfer of energy that slows Phobos down, gradually pulling it closer to Mars.

Phobos Orbits Mars Eastward with a Shorter Period Than Mars