We could learn even more about the atmosphere from NASA's Mars Atmosphere and Volatile Evolution Mission orbiter, which is expected to launch in November. This spacecraft will have techniques to measure the current rate of loss of the atmosphere.
5. Radiation makes the trip to Mars dangerous for humans. Curiosity spent 253 days getting to Mars in 2012. During that time, the mission (officially called Mars Science Laboratory) was collecting data about radiation on the journey to the Red Planet using the Radiation Assessment Detector device.
An analysis of this data, published in the journal Science in May, found that Mars-bound pioneers would be exposed to radiation levels that could effectively retire astronauts under NASA's current standards.
"The radiation environment in deep space is several hundred times what it is on Earth, and that's even inside a shielded spacecraft," said Cary Zeitlin, principal scientist for the Martian Radiation Environment Experiment. Scientists are working on faster engines to shorten the trip to Mars, and may be able to conceive of a spacecraft with better shielding.
What's next? Drive, drive, drive!
The rover's second year will be mostly about the five-mile drive to Mount Sharp, Vasavada said.
So far, Curiosity has stopped a lot to test out its instruments, collecting and analyzing samples and exploring particular areas. Now, it will drive as far as it can every day -- but not at Earthly highway speeds. Vasavada's hope is to get the rover to Mount Sharp by next summer.
During the drive, the rover will continue snapping photos, and the meteorological instruments will still take measurements. Curiosity will stop if it spots anything -- a structure or formation, or the improbable Martian -- that looks interesting to scientists.
In 2020, another NASA rover is planned to join the small fleet of human-made vehicles on Mars. This one may be able to collect samples for potential return to Earth, and test technology relevant to human exploration.
Meanwhile, the Opportunity rover rolls along, in its 10th year, exploring Mars on the opposite side of the planet from Curiosity.
None of these rovers may ever meet. But perhaps their tracks will mark the paths where humans will someday tread.