HEMATITE

"Hematite is a special place. It's one of three sites on Mars with detectable mineral signatures for coarse grained hematite." This type of Hematite generally forms in water, so "finding hematite is like finding a sign that says 'Water Was Here!'"

Not only does it rank high in scientific interest; Hematite measures high on the safety scale as well. Of the four sites, Golombek said, Hematite is very unique: "it's one of the smoothest, flattest, safest place in the equatorial region. All the other sites have good things about them and not-so-good things about them."

MELAS

The Melas region is a canyon with 10-kilometer high walls (6 miles high) that "make the Grand Canyon look insignificant," said Golombek. "There is a area at its very center that has interior deposits that look like some type of sedimentary rock. Did these rocks form in water, was there a lake there? Were the layers deposited by water? Are they due to wind erosion or some other process? It's a prime place to address very important questions."

Attractive though it is, said Golombek, Melas is surrounded by sand dunes. A bullseye in targeting would put the lander in fascinating terrain, but anything short of that could be disappointing.

GUSEV CRATER

"Gusev is perhaps the classic crater that looks like it was a crater lake," said Golombek.. "For all the world, it looks like a crater that filled with water, which at some point breached the crater wall and the water escaped. If this occurred, the crater should be filled with sediments deposited in the lake." And if the sediments are there, they were laid down in watery solutions that will provide valuable clues in the search for water's past on Mars.

The original landing ellipse considered for Gusev was found to contain some rough-looking terrain in Mars Global Surveyor data, so the ellipse was moved to gentler terrain slightly to the west.

ATHABASCA VALLES

Finally, there's Athabasca Valles in the Elysium Planitia, or the "Plains of Elysium." "It is one of the youngest outflow channels on Mars," said Golombek. "It's hundreds of kilometers long with a catastrophic outflow channel, kind of like Ares Valles where Pathfinder landed. Geologically, it's very young, just tens to hundreds of millions of years old." The channel has been worn by water and has young volcanics as well, making it a prime location to look for hydrothermal deposits.