QUESTION:
It appears that from the meteorological data that the variation in
temperature during a martian day is about 70 degrees centigrade.  This
compares with the earth's variation of about 20 to 30 degrees farenheit,
considerably less.  (A factor of about 5 to 1)

This does not consistent with the fact that Mars is considerably farther
from the sun than is earth and thus would be subject to less solar heat
during the day. On the other hand, variation in daily temperature seems to
be due to two factors, solar heating and night time heat radiation.

Apparently, on Mars, solar heating is less being farther from the sun but
night time radiation must be much more. But since the martian atmosphere is
much less dense than that of the Earth, there may be less latency of ambient
temperature thus more radiation during the Martian night.

Why is the Martian daily variation in temperature about 5 times that of
Earth?

ANSWER from Bob Haberle on August 3, 1997:
This is a very good question. There are a number of factors to consider.
First, Mars has no liquid water on its surface, while the Earth does. A good
deal of the solar energy reaching the surface of the Earth goes into
evaporating the water and so the temperature climb during the day is
throttled by this effect. Of course in the deserts this is not a big issue,
but then again the deserts behave like Mars. The other factor to consider is
the thinness of the Martian atmosphere and the fact that its main
constituent, CO2, is radiatively active only in the 15 micron band. This
means the atmosphere can respond very rapidly to changes in the ground
temperature and so it can heat up rapidly during the day. But at night, the
atmosphere cannot prevent most of the ground's radiant energy from escaping
to space. Hence, the surface can cool much more than here on Earth where a
variety of greenhouse gases can slow the cooling rate at night.

Robert M. Haberle
Space Science Division, MS 245-3