Based on spacecraft and Earth-based observations of Mars, we have a good
understanding of the annual cycle of water vapor in the Martian atmosphere.
The most important source of this water is the north residual polar cap
from which large quantities of water vapor sublime during late spring and
early summer. The apparent regularity of the cycle allows us to make a
model prediction of today's atmospheric
water vapor distribution on Mars. Note that the total amount of water
in the atmosphere is very small (measured in precipitable micrometers). If
all the water in the Martian atmosphere were to rain out at any given time,
it would make a puddle less than a hundredth of a centimeter deep!
Detailed computer modeling allows us to infer that there is another significant
reachable reservoir of water on Mars, besides the polar caps and the atmosphere.
Approximately 10 times the total atmospheric inventory of water can be found
adsorbed in the top few centimeters of the Martian soil. This could represent
an important resource and will be the object of future landed spacecraft
missions. Indications are that this adsorbed water supplies much of the
atmospheric water vapor that exchanges between the hemispheres during the course
of the Martian year.
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Curator: Howard Houben
Responsible NASA Official: Jeffery Hollingsworth