NASA says its Mars Atmosphere and Volatile Evolution spacecraft has successfully performed the first of five scheduled "deep dip" maneuvers to gather data in the lower reaches of the red planet's upper atmosphere.
The lowering of the Mars Atmosphere and Volatile Evolution's (MAVEN) orbit 16 miles below its previous lowest point, to around 78 miles above the Martian surface, allowed it to gather measurements at atmospheric densities 10 times greater than at its normal orbit, which ranges from 93 miles and up.
"During normal science mapping, we make measurements between an altitude of about 150 km and 6,200 km (93 miles and 3,853 miles) above the surface," says Bruce Jakosky, principal mission investigator at the University of Colorado's Laboratory for Atmospheric and Space Physics in Boulder. "During the deep-dip campaigns, we lower the lowest altitude in the orbit, known as periapsis, to about 125 km (78 miles) which allows us to take measurements throughout the entire upper atmosphere."
In the initial "deep dip" beginning Feb. 10 and lasting eight days, MAVEN spent the first three days slowly reaching periapsis, then a full five days gathering data during 20 orbits.
During those orbits Mars rotated beneath the spacecraft, allowing the probe to sample the atmosphere at different longitudes around the entire planet.
The descent to the lower orbit was done slowly, with three separate firings of the probe's rocket motors, out of concern that one large burn might send it too deep into the atmosphere, NASA said.
The gentler burns allowed controllers to "walk" the spacecraft to a lower altitude in several smaller steps, said NASA.
"Although we changed the altitude of the spacecraft, we actually aimed at a certain atmospheric density," says Jakosky. "We wanted to go as deep as we can without putting the spacecraft or instruments at risk."
Even the thin atmosphere of Mars can cause noticeable drag on the probe, and going too low -- into a region of too high atmospheric density -- could increase drag to the point where the spacecraft could begin to heat up, with possible damage to it or its instruments, controllers said.
After the deep dip, a series of maneuvers was conducted to bring MAVEN back up to its normal operational altitude.
Scientific data collected during the dip will be analyzed in the coming weeks, scientists said.
One of MAVEN's primary goals is to gain an understanding of how gases in the Martian atmosphere are being lost into space, and the ways that loss has affected the red planet's climate throughout its history.
That's why MAVEN is tasked with gathering data from more than one layer of the atmosphere.
"We are interested in the connections that run from the lower atmosphere to the upper atmosphere and then to escape to space," says Jakosky. "We are measuring all of the relevant regions and the connections between them."
MAVEN was launched in November 2013 and entered the orbit of Mars in September, 2014.
