Mission: Putting Mars on the Map
They are postcards from Mars--unique vistas of jagged polar icescapes, sand dunes curling like mustachios across blush plains, and layer cakes of rock miles thick hinting at a volcanic fury that may still burn at the heart of the red planet.
As it orbited the planet for the past year, the Mars Global Surveyor spacecraft sent home 2,000 images from its high-resolution camera. Each picture, snapped as the craft skipped in and out of the atmosphere to brake itself like a stone hurled across an interplanetary pond, is between 20 and 40 times sharper than any previous snapshots of the planet.
The images are a tantalizing prelude to a flood of scientific data now streaming to Earth from the instruments aboard Global Surveyor. The spacecraft this week began the mission for which it was designed--a systematic investigation of the planet for the 687 days of one full Martian year.
The spacecraft already has transmitted as many images in the last three weeks as in the previous year.
“Almost every image is a surprise,” said Surveyor project scientist Arden Albee at the Jet Propulsion Laboratory. “The total effect will be to change all of our thinking about Mars.”
Eager planetary scientists--some of whom have waited 14 years for the opportunity to bring the solar system’s fourth planet into sharper focus--already are using the new readings “to rewrite the encyclopedia of Mars,” said Surveyor project manager Glenn E. Cunningham at JPL.
Geophysicist Maria Zuber at the Massachusetts Institute of Technology is using the laser altimeter aboard Surveyor to create the most detailed surface maps yet of Mars. “I am getting a million measurements a day,” she said. “What we have gotten in the past three weeks you wouldn’t believe.
“If our laser hangs on for the full two years,” Zuber said, “we will have a much better topographical map of Mars than we will have of the Earth.”
Red Alert
The new insights into the Martian landscape are an unexpected benefit of an engineering emergency that--but for the ingenuity of mission planners at JPL and Lockheed Martin Astronautics in Denver--might have doomed the $250-million spacecraft and its long-anticipated examination of Mars.
When it arrived at Mars in 1997, the Global Surveyor was the first U.S. spacecraft to orbit the planet in more than 20 years, the vanguard of a small fleet of Mars probes now approaching the planet. Its six instruments are duplicates of those aboard the ill-fated, $900-million Mars Observer, which disappeared in space in 1993, three days before reaching Mars.
Throughout its 10-month voyage to Mars, however, the Global Surveyor had nursed a broken solar panel. While it posed no danger en route, mission planners were afraid that the dangling, 11-foot-long panel would fold up on itself or snap off during the aerobraking maneuvers, in which the pressure of the atmosphere is used to slow spacecraft slightly during each orbit.
To avoid the potential catastrophe, NASA redesigned the mission and eased the spacecraft more gently into orbit.
The result delayed the start of the official mapping activity by a year and added $11 million to its cost, as engineers gingerly used the friction generated by the Martian atmosphere to slow the craft over the course of some 1,400 elliptical orbits around the planet, three times more than planned.
The part that failed on the solar panel was a hydraulic damper designed to make sure the apparatus unfurled gently. A similar damper is also part of the spacecraft’s main antenna system. Until last week when the main antenna was safely deployed, NASA officials were worried that it too might break, which would have drastically curtailed the mission.
Indeed, space agency officials were so concerned that they held off deploying the antenna for three weeks so the probe could gather and relay what researchers called “contingency science.” That way, if there was an antenna malfunction, the mission would not be a complete loss. Once the high-gain antenna unfurled properly last week, they were ready to begin the mission in earnest.
“Having a deployed, or steerable, high-gain antenna is like switching from a garden hose to a fire hose in terms of data return from the spacecraft,” said flight operations manager Joseph Beerer at JPL.
A Dream Come True
The unexpected benefit of all these engineering improvisations to slow the craft was the opportunity to study Mars for an extra year from an entirely different orbital perspective than originally planned. At the low end of each braking orbit, the spacecraft came four times closer to the surface than it is expected to reach during the mapping portion of the mission, allowing for more detailed observations.
In a sense, “they got a mission they never planned on,” said Zuber. “To get this kind of data, they would have had to send another spacecraft to Mars.
“Given that we still have the whole mapping mission ahead of us, the past year was something very special,” she said. “In your wildest dreams you wish something like this would happen.”
So far, the spacecraft’s preliminary scientific survey of the Martian surface, atmosphere and interior has revealed:
* Volcanic or sedimentary rock bedded in layers six miles deep. The layered deposits form the walls of the Valles Marineris canyon, which runs for 2,400 miles. Although researchers can’t identify the type of rock, they said the formation most likely is evidence that volcanic activity played a much larger role in shaping the planet’s surface than previously believed.
* Recent lava flows, suggesting the planet may still be active volcanically. A systematic survey of impact craters, which can be used to gauge the age of lava flows and other geographic features, suggests that some areas of volcanic activity may be only 50 million years old, much younger than previously believed.
* Erosion by ground water, most likely from subterranean reservoirs. No one knows if those reservoirs still exist, but images reveal meandering river beds and broad channels that could only be sculpted gradually by water flowing for an extended time, rather than by flash floods as some have speculated. No one knows the source of the water, but so far the instruments have turned up no evidence of rainfall.
* A chemical suggestion of ancient lake beds. In some areas, Surveyor’s thermal emission spectrometer has detected a precipitate of a coarse-grained, iron-rich mineral called hematite that usually only forms in large bodies of standing water. The Surveyor’s altimeter shows the northern hemisphere to be so flat that some scientists suggest much of it may be ancient ocean floor.
* Fragmentary relics in the planet’s crust of an ancient magnetic field like Earth’s, but no contemporary planetary magnetic field. The atmosphere itself is much more variable than anyone expected, shrinking and swelling by as much as 70% from one day to the next.
“Mars is a far more complex place than anyone has given it credit for,” said Michael Malin, head of Malin Space Science Systems in San Diego, which designed and operates the Surveyor camera.
“Traditionally, people have thought of Mars as the moon with an atmosphere,” Malin said. “Mars is not the moon with an atmosphere. Mars is Earth with craters. It has the Earth’s complexity.”
