MAVEN’s primary mission includes five 5-day “deep-dip” campaigns, in which the periapsis (lowest point in the orbit) is lowered from about 93 miles (150 km) to about 77 miles (125 km). The first “deep dip” maneuver will begin on Tuesday, February 10, 2015, with a two-day “walk down” into the target density corridor of 2.0 – 3.5 kg/km3. The density of Mars’ atmosphere in the current science-mapping orbit is about 0.12 kg/km3.
The “deep dip” campaigns will provide data from the boundary where Mars’ upper and lower atmospheres meet—also referred to as the “homopause”—enabling the spacecraft to sample the entire upper atmosphere of Mars for the first time.
Thanks to NASA’s MAVEN Mission to Mars