Stopping Mars

Hi, my friend says that he saw on a news programme that mars had temporarily stopped rotating on its axis. I don’t believe such a wild story. which of us is wrong? is it even possible?
- david (age 18)
UCL , England

That story is completely nuts. Angular momentum is conserved, and there’s no easy way for a planet to lose all of its angular momentum.

Mike W.

Actually, what the news story may have badly conveyed is that the position
of Mars in the sky is a complicated function of time. If you watch
Mars night after night, it appears to move against the starry
background. But Mars is orbiting the sun and Earth too is orbiting
the sun. The stars nearby Mars in the night sky are the ones close to
a line you can draw from Earth to Mars and continue off far away.
Because Earth’s year is shorter than Mars’s, and Earth’s orbit
is inside Mars’s, which way this line points sometimes advances
forwards, and sometimes starts moving backwards.

Here’s a good link from NASA:

Tom

(published on 10/22/2007)