So far, Curiosity has found evidence of a past habitable environment on Mars. The rover's ultimate destination, Mount Sharp, may hold a record of the transformation to colder, dry conditions.
NASA's Curiosity rover achieved prime mission status on June 24 as the rover also known as the Mars Science Laboratory logged one Martian year, 687 Earth days, on the surface of the red planet.
The $2.5 billion mission quickly achieved one of its primary mission objectives, detecting evidence of a past Martian environment conducive to the rise of microbial life, at a site dubbed Yellowknife Bay soon after touching down. At Yellowknife, Curiosity drilled into "mudstone" revealing mineralogy from a former lakebed once in contact with water of neutrality suitable for biological activity -- not too acidic or too alkaline.
There have been setbacks as well for the nuclear-powered mechanical geologist: unexpected wear on the big wheels that give Curiosity its mobility.
Launched on Nov. 26, 2011, the one ton Curiosity dropped to the surface of the vast Martian Gale Crater on Aug. 6, 2012. The delivery unfolded in spectacular fashion with a first time entry, descent and landing strategy that featured the sky crane, a parachute and retro rocket slowed platform that hovered over the desert-like terrain, while it lowered its 10 instrument payload to the surface with lanyards.
Since touching down, Curiosity has covered 4.9 miles -- despite unexpected wheel wear from sharp embedded rocks. The damage, noted in late 2013, resulted in a change in course on the path to Mount Sharp, the mission's ultimate destination.
Mount Sharp, Curiosity's destination, looms on the horizon. NASA
The new route features a sandy surface with fewer sharp-edged rocks. As it approached its first Martian anniversary, the rover was 2.4 miles from Mount Sharp and pursuing a gentler course charted with the help of NASA's long running Mars Reconnaissance Orbiter. MRO has been circling the red planet since March 2006, and its long life enabled mission planners to plot a new path through dune-like features to Sharp's northern flank.
"When you're exploring another planet, you expect surprises," notes Jim Erickson, the Curiosity project manager at NASA's Jet Propulsion Laboratory. "The sharp, embedded rocks were a bad surprise. Yellowknife Bay was a good surprise.”
Curiosity's last stop for science this spring, Windjana, yielded the mineral magnetite. Samples from Windjana still aboard Curiosity await analysis and a determination of whether the magnetite was inherent in the host lava material or arose from exposure to water later. Windjana also revealed orthoclase for the first time on Mars, a mineral common in the Earth's crust.
At Mount Sharp, mission scientists expect to encounter geological layering that will reveal more about changes in the Martian environment, a transformation from a seemingly warmer, wetter realm in the distant past to the cold, dry conditions evident today.
Other findings from Curiosity suggest a once thicker atmosphere was depleted at high altitudes, perhaps stripped away by the solar wind.
The rover's observations hint at little, if any, methane in the thin atmosphere -- a gas whose potential sources include biological activity.