NASA has launched its latest mission to Mars, which is devoted to understanding the upper Martian atmosphere.
The $671m (€496m) mission will study how the planet most like Earth in the solar system lost its water.
An unmanned Atlas 5 rocket blasted off from Cape Canaveral Air Force Station in Florida in the US this evening.
Unlike previous Mars probes, the Mars Atmosphere and Volatile Evolution Mission (MAVEN) will not be looking at or landing on the planet's dry, dusty surface.
Instead, it will scan and sample what remains of the thin Martian atmosphere and watch in real-time how it is peeled away, molecule by molecule, by killer solar radiation.
The journey to Mars will take ten months.
The satellite, tucked inside a protective nose cone, lifted off aboard a United Launch Alliance Atlas 5 rocket at 1.28pm local time (6.38pm Irish time).
Upon arrival, MAVEN will fire its braking rocket to put itself into a highly elliptical orbit around Mars, which will allow it to dip down as close as about 105km from the ground to gather air samples for analysis.
At its highest point, MAVEN will be about 6,000km away, a vantage point for measuring how much and what types of radiation are sweeping past the planet from the sun and cosmic sources.
The point of the project is to determine how much of the atmosphere is being lost to space today and extrapolate back in time to figure out what was happening in the past.