Mars Surveyor
Twenty years after twin Viking orbiters sent us images
of Mars' giant volcanoes and canyons, a new probe is
now working on the red planet.
After a year-long delay, NASA's Mars Global Surveyor
is mapping the dusty, frozen planet from a 240-mile-high
polar orbit, using a camera powerful enough to detect
objects the size of a Volkswagen beetle. Surveyor also
carries instruments that will search for prime landing
sites for future landers and may help scientists discover
what turned Mars' once-warm, water-harboring surface into
a frozen, desert of shifting dunes.
Launched in November 1996, Mars Global Surveyor reached
Mars orbit in September 1997, two months after Mars
Pathfinder landed on the surface and deployed a rover,
grabbing headlines worldwide. But to most planetary
scientists, it was the arrival of Surveyor _ not Pathfinder
_ that had been eagerly awaited. "This mission will tell us
more about Mars than all of the previous missions combined.
It's been a long time coming and of course we're very
eager," said Glenn E. Cunningham, deputy director of the
Mars Exploration Program at the Jet Propulsion Laboratory
in Pasadena, California. "This sets the stage for everything
that follows," he added.
For a full 687-day Martian year, Surveyor is
observing Mars' shifting weather patterns and waxing and
waning polar caps. The probes' instruments are collecting
data about its weak magnetic field and the distribution
of its surface minerals. And there is always the chance
of finding extinct hot springs or lingering volcanic
hot spots.
Even before mapping began March 9, Surveyors' camera had
used the long aerobraking mission to snap thousands of
photographs, some taken from as close as 100 miles _
140 miles closer than the eventual mapping orbit. Those
images showed extensive layering in the walls of Valles
Marineris, a canyon 2,400 miles long. Scientists believe
that's evidence volcanoes spewed 10 times more lava onto
Mars during its first 3 billion years than had been
previously believed. There were also signs of eruptions
as recent as 40 million years ago and tantalizing photos
of the rust-colored planet's meandering river valleys and
dune fields.
Surveyors' Improvements Over Viking
Surveyor is taking wide- and narrow-angle photographs for
a global view at least 20 times sharper than those produced
by the Viking orbiters in the late 1970s.
The Viking cameras took about 55,000 images, most showing
objects only as small as 150 feet. But Surveyor can see
objects smaller than 10 feet across, according to Michael
Malin, the mission's top camera scientist. "We're seeing
individual rocks the size of cars, something we've never
seen before. The most exciting thing is right now we're
seeing things we can't explain, geological landforms that
challenge us."
Where the Viking I probe photographed the famous "Mars
Face" some people saw as evidence of a civilization on
Mars, Surveyors' superior optics revealed it as nothing
more than a bumpy hill in late afternoon shadows.
The Big Question
Surveyor's laser altimeter is measuring the highs and
lows of Mars' polar caps, volcanoes and gorges; its thermal
emission spectrometer is mapping the planet's surface
minerals. That map may show shorelines of ancient lakes
or evidence of extinct hot springs where Martian life _ if
it ever existed _ could have thrived.
Or maybe it will answer the main question about Mars:
what happened to all the water scientists believe carved
its gorges and valleys. Is it frozen underground, or did
it evaporate into space? "It's absolutely the big mystery
and it's closely connected with the question of life.
Where did all the water go?" said Dr. Arden Albee, the
Surveyor's project scientist at the California Institute
of Technology in Pasadena, Calif.
To see the latest images sent back
by the Mars Global Surveyor,
visit the mission's Web site:
Mars Exploration Program
