Mars the land of Opportunity

NASA's second lander arrives on red planet to study gray hematite

Jan 26, 2004
Sam Jaffe(

With the successful landing of the Opportunity lander on Saturday (January 24), NASA is now suffering from a rare embarrassment of riches: two Martian rovers on the brink of exploring very different geological realms of the red planet. The news got even better the next day when NASA announced that the malfunctions on the Spirit rover appear to be fixable software glitches that can be recoded. Engineers expect to get Spirit up and moving again within 2 weeks.

Now that both rovers appear to be back on their feet—or wheels—they are set to explore two very different places. At the heart of the geological differences are the little silvery pendants that Brian M. Hynek handed out on Saturday night to partygoers at his lab as they watched the Opportunity landing unfold live on TV. The research associate in the University of Colorado's Laboratory for Atmosphere and Space Physics gave each person a shiny little rock that resembled polished silver and that cost him about 5 cents apiece. Those guests and the Opportunity rover had something in common: they were both about to become a lot more familiar with gray hematite. “This mission is to look for gray hematite and analyze it,” Hynek told The Scientist.

“I can't think of a better set of tools on a rover to accomplish that,” he said, referring to the Rock Abrasion Tool, the Mossbauer spectrometer, as well as the microscopic imager on board. “There's no such thing as absolute proof in planetary science, but this is about as close as we'll ever get to it. At the end of the Opportunity mission, we'll know how the hematite was formed.”

As the first shots from the Terra Meridiani (also called the Meridiani Planum) showed, Opportunity's new home is a vastly different place from the Gusev Crater, where Spirit set up shop. According to spectrometer readings from the Mars Global Surveyor, around 15% of the Terra Meridiani's regolith consists of gray hematite, a crystal that is usually formed with the presence of massive amounts of water.

Not to be confused with red hematite, the ubiquitous rust that covers the surface of Mars and gives the planet its reddish tint, gray hematite is found in large concentrations in only a few places. Of those spots, the Terra Meridiani has the largest gray hematite presence—a several hundred square kilometer outcropping of basalt and gray hematite.

How did this unusual mineral get there? There are eight known formation mechanisms for gray hematite, and seven of them involve a lot of water. On the other hand, the gray hematite may have come from volcanic eruptions from millions of years ago, which means that water wasn't necessary for its creation, according to Hynek. But his theory is that groundwater produced the hematite/basalt aggregate, and then the steady erosion of the Martian surface revealed the rock. The Valles Marineris, a canyon that's the length of the United States and some 100 kilometers in width, also exhibits small deposits of hematite that may also be associated with water.

“The Valles Marineris is one of the most scientifically interesting places on Mars, especially in the search for water,” said F. Scott Anderson, a geophysicist at the University of Hawaii's Institute of Geophysics and Planetology. Anderson points out that dropping a lander inside the Valles was too risky, but studying the Terra Meridiani may be the next best thing. “Because both Meridiani and the Valles Marineris have the same type of mineral deposits, and both areas appear to have been associated with water, the Meridiani site may be able to tell us a lot about the presence of water in the canyons,” Anderson told The Scientist.