Washington, Feb 20 (IANS): NASA's Mars Atmosphere and Volatile Evolution (Maven) spacecraft has completed the first of five deep-dip manoeuvers designed to gather measurements closer to the lower end of the Martian upper atmosphere.

"During normal science mapping, we make measurements between an altitude of about 150 kms and 6,200 kms above the surface," said Bruce Jakosky, MAVEN principal investigator at the University of Colorado.

"During the deep-dip campaigns, we lower the lowest altitude in the orbit, known as periapsis, to about 125 km which allows us to take measurements throughout the entire upper atmosphere," he said.

The 125-km altitude difference may not seem like much but it allows scientists to make measurements down to the top of the lower atmosphere.

"We are interested in the connections that run from the lower atmosphere to the upper atmosphere and then to escape to space," said Jakosky.

The first deep dip campaign ran Feb 10 to Feb 18.

The first three days of this campaign were used to lower the periapsis.

Each of the five campaigns lasts for five days allowing the spacecraft to observe for roughly 20 orbits.

Since the planet rotates under the spacecraft, the 20 orbits allow sampling of different longitudes spaced around the planet, providing close to global coverage.

One of the major goals of the MAVEN mission is to understand how gas from the atmosphere escapes to space and how this has affected the planet's climate history through time.

In being lost to space, gas is removed from the top of the upper atmosphere.

But it is the thicker lower atmosphere that controls the climate.

"MAVEN is studying the entire region from the top of the upper atmosphere all the way down to the lower atmosphere so that the connections between these regions can be understood," Jakosky said.