The quest to explore a rust-colored world that has captured humanity's imagination enters a new phase with Wednesday's scheduled launch of the Mars Reconnaissance Orbiter.
From NASA's first successful Mars flyby 30 years ago to the twin rovers scuttling across Martian craters today, scientists have only scratched the surface in describing how the planet is put together, how it evolved, and most provocatively, whether it had - or still has - conditions that could cradle simple life forms.
Now, scientists aim to get under Mars' skin.
"We're moving from exploration to intensive investigation" using an orbiter bristling with "the most powerful suite of instruments ever sent to another planet," says Douglas McCuistion, who heads NASA's Mars Exploration Program.
The orbiter tips the scales at just under 2-1/2 tons. It carries radar that can penetrate up to a mile beneath the surface, a telescopic camera capable of spotting objects as small as a dining room table, a high-resolution spectrometer that will rewrite the Mars version of the "Golden Book of Rocks and Minerals," and a communications system whose capacity to beam information back to Earth dwarfs that of all previous orbiters combined. Straws that dribbled data are yielding to a fire hose.
Like its recent predecessors, the Mars Reconnaissance Orbiter (MRO) focuses on water - as sculptor, climatic thermostat, ingredient for life, and as a resource for future manned missions to the red planet. Past missions have shown that water carved its "initials" all over the Martian surface and left its signature in minerals there. Evidence suggests that significant amounts of water - as ice or trapped in minerals - reside in subsurface layers near the poles and at lower latitudes.
The MRO mission, however, promises to "really advance our understanding of the processes that shaped the Martian surface," says James Head III, a planetary geologist at Brown University in Providence, R.I.
The radar's pulses and echoes, for example, not only will probe for water-ice. They also are expected to yield 3-D images of ancient geological structures buried beneath more-recent lava flows or beneath layers of material blasted across the surface by meteor impacts. Understanding the density and structure of the crust is critical to reconstructing pathways for groundwater flow in Mars' past, Dr. Head notes.
On Earth, underground hydrothermal systems teem with simple life forms. Such systems are believed to have permeated Mars' crust during the planet's first billion years, reaching as deep as 30 miles or more. Radar could verify their presence and map their extent, and enable scientists to match them with surface locations where future missions could drill for samples.
MRO is not the only craft flying this type of radar. The European Space Agency's Mars Express orbiter, currently circling the planet, finished activating its surface-penetrating radar last month. While it can peer deeper into the crust - up to three miles - it can spot features about 500 feet across. The radar on MRO can zero in on features as small as 66 feet. Indeed, scientists anticipate that the Mars Express radar will spot features within the first mile of the surface that may be worth a more detailed look with MRO.
NASA's orbiter also carries a high-resolution version of the spectrometer that Mars Express carries. Where Mars Express can map mineral deposits as small as 660 feet across, the MRO spectrometer will focus in on features roughly the size of a house. At that scale, Head explains, the MRO will be able to glean the mineral makeup of rocky outcrops that current missions can't detect.
One area of interest: The Mars' North Pole region, where water's role in shaping the surface has been the subject of debate. Mars Express scientists recently reported discovering small patches of calcium-rich sulfates there. These form in the presence of water and get left behind as water evaporates. The water could have come either from acidic snow's interaction with surface minerals or from melting ice as the planet underwent a warm period. A more detailed look could help explain the mineral's presence.
Overall, the keys to this new phase of Mars exploration are spotting the planet's smaller features and boosting the volume of collected data, notes Sue Smrekar, the MRO's deputy project scientist at NASA's Jet Propulsion Laboratory in Pasadena, Calif. "Every time we look at the planet in greater detail, it tells a different story."