NASA on Monday launched an unmanned spacecraft toward Mars to study the planet's atmosphere.
A United Launch Alliance Atlas V 401 rocket carrying the Mars Atmosphere and Volatile EvolutioN (MAVEN) craft blasted off on schedule at 1.28pm local time. The journey will take 10 months.
Much of MAVEN's mission will be spent circling the planet 6000km above the surface.
However, it will make five deep dips to a distance of 125km above the landscape to get readings of the atmosphere at various levels.
A BBC science correspondent said the evidence suggests the planet was once shrouded in a thick blanket of gases that supported the presence of liquid water at its surface. Today, the air pressure is so low that free water would instantly boil away.
The present-day atmosphere of Mars, composed mostly of carbon dioxide, is extremely thin, with atmospheric pressure at the surface just 0.6% of the Earth's surface pressure.
NASA has sent a series of rovers to explore the surface of the Red Planet, including its latest, Curiosity, which arrived last year.
A craft launched earlier this month by India will seek to find traces of methane from Mars.