The molecules detected in the atmosphere of Mars are telling scientists about the nature of the environment and its transition from a warm, wet planet to a cold, dry one. The rover Curiosity has been on Mars almost three months.

The rover Curiosity has sent back its first sniff of the Martian atmosphere, and NASA scientists are analyzing what the findings mean about the habitability of the planet at some time in the past.

The Sample Analysis at Mars (SAM) instrument, seen here before the mission launch, took that deep breath of Martian air. Scientists said the molecules in the air samples indicate that Mars has lost a significant amount of its atmosphere.

"This thin blanket of an atmosphere provides a window into the Martian past," Mars Science Laboratory lead scientist Michael Meyer said at a November 2 press briefing from the mission control center at the Jet Propulsion Laboratory in Pasadena, California. "The measurements of methane, carbon dioxide and argon are key to helping us understanding the Martian atmosphere and when the planet could have supported microbial life."

SAM is the largest of the 10 science instruments on the rover, now approaching three months since the spacecraft descended to the surface of the Red Planet.