Weather reports from Mars, global mapping, inspection of potential
landing sites, more data about the red planet than from all previous
missions - no problem for the hardworking Mars Global Surveyor spacecraft.
In fact, the Global Surveyor has been so successful that it earned an
extension following conclusion of its prime mapping mission early in
2001. The second extension began in April 2002 and will continue
the mission into late 2004.
"Things are going well," said Tom Thorpe, Mars Global
Surveyor project manager at NASA's Jet Propulsion Laboratory in
Pasadena, Calif. "We've accomplished all of our primary mission
objectives to date and the science instruments have returned a
tremendous amount of data. Now we're looking forward to all the
science to come in the second extension."
Thorpe looks forward to Surveyor's second extension.
In addition to mapping operations, the spacecraft is targeting images
of potential landing sites for the 2003 Mars Exploration Rovers. In its
extended mission, the Surveyor has been given latitude to take pictures at
different angles and target areas missed in the prime mission.
A Beautiful View
One of the tasks that scientists want to do is obtain stereo
(three-dimensional) images of some areas already covered. To do this,
the spacecraft has to be pointed off-nadir. Nadir is the point directly
below the observer; hence if the spacecraft is "tipped," the
target can be imaged up to 30 degrees away from the original ground
track. When a place imaged from one angle is pictured again from another
angle, the images can be overlaid to create a stereo picture.
Artist's concept of the Mars Global Surveyor in a downward-pointing nadir position and an off-nadir slightly backward-pointing position.
This technique is useful for providing dramatic views of the planet's
surface and to study the vertical profile of its atmosphere. For example,
scientists want as complete a picture as possible of potential landing
sites for the 2003 Mars Exploration Rovers. The stereo images taken
by Global Surveyor will help substantially in the final site selection.
"There is still so much to learn about Mars," said Mars
scientist Dr. Ken Edgett, Malin Space Science Systems, San Diego,
Calif. "Our high-resolution camera is testing hypotheses formulated
over the past two decades using Mariner 9 and Viking data and even
new theories from Surveyor and Mars Odyssey images. We're seeking
to understand previous observations, and to monitor changes that are
taking place due to weather and changes in polar frost."
So How's the Weather on Mars?
Mars has seasons, just as Earth does. Using the Mars orbiter camera on
Surveyor, scientists are now able to monitor the red planet's weather
changes from one martian year (about twice as long as an Earth year) to
the next. One of their discoveries has been that the southern polar ice
cap, long thought to be permanent, isn't so permanent.
Springtime at Mars' southern polar cap
"What we're finding is just short of incredible," said
Edgett. "For most of the Mars year, the weather patterns are very
predictable. Last year, in late June, we had global dust storms that
obscured the planet for three months - an event that did not fit the
patterns we'd otherwise seen. We found that there were lots of storms
going on at once, not that there was one gigantic global dust storm, as
was thought during previous events."
Thorpe said, "The weather reports are very important, since
weather will affect future spacecraft landings and operations on the
surface of Mars, including the 2003 Mars Exploration Rovers."
Weekly Mars weather reports are available by going to the Mars
Exploration page at http://marsprogram.jpl.nasa.gov
and clicking on the How's the Weather on Mars box.
Students interested in exploring Mars further can go to
for more information on the red planet.
Extensions Lead to Discoveries
"One of the reasons I'm so very excited about the
second extension is because every week there is something
new and surprising in our data," said Mars scientist Ken
Edgett. "And what's really cool is that every four to six
months we discover something totally amazing. Last year, we
were flabbergasted to find that the southern polar
"permanent" ice cap isn't so permanent. We're
now tracking changes to the cap on shorter time scales."
Each winter, frost forms a seasonal polar cap covering
everything from 60 degrees latitude to 90 degrees latitude;
it retreats in spring. The permanent ice cap, which is mostly
carbon dioxide, remains through the entire summer and was
previously thought to be permanent.
"We now know that even in summer the ice is
subliming (converting directly from solid to vapor) at a rate that
suggests the entire cap could disappear in a few thousand to
tens of thousands of years," said Edgett. "There's
a lot of carbon dioxide in the permanent cap, but we're finding
that it is going away on a larger time scale
[than the seasonal frost], independent of season."
For more information and images, please see