Expert: Tom Whiting - 2/27/2004

Question
Hello,

I know that Mars' spin axis has a similar tip angle to that of Earth, but why does this cause seasonal temperature variations on Mars?
and what causes the Martian summers and winters to differ between the northern and southern hemispheres?

Thanks  

Answer
Kai,
Yes, Mars 25 degree axial tilt gives Mars 4 seasons, just
like the Earth, during its 687 day (1.88 year) orbit around the sun.  BUT, an additional factor gives Mars more
extreme summers and winters because you have to factor
in its variable distance from the sun.
(With the Earth, distance between perihelion (91.5 million
miles) in January and aphelion (94.5 million miles) in July,
amounts to only about a 3% difference, thus Earth's seasons are only affected by about 3% due to solar distance, hardly
noticeable.

But with Mars, in a much more elliptical orbit than the Earth, the difference between perihelion and aphelion are much, much greater, thus producing much wider swings in the Martian climate....much warmer summers and much colder winters....then what the Earth's differential, produces.

So in Mars case, distance from the sun (in addition to the
axial tilt) is a much bigger factor than here on Earth,
probably accounting for up to half of the Martian seasonal
changes.   (Whereas on Earth, distance from sun accounts
for a lowly, hardly measureable, 3%....the axial tilt of
the Earth accounts for the other 97% of seasonal change.

Hope this helps,
Clear Skies,
Tom Whiting
Erie, PA


FOLLOW UP:
Oh, sorry, I didn't see the last part of your question...
well, the Mars southern hemisphere is tipped toward the
sun during perihelion, and away from the sun during aphelion, so Mars southern hemisphere would have much more
extreme climate changes than the northern hemisphere.
And in fact thru our scopes last August, a very favorable
opposition occurring within hours of Mars perihelion, we
watched the S. Polar Cap almost completely melt (or sublimate) right in front of our eyes in a matter of a few weeks.