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MAVEN starts weighing the air Mars loses

The first orbiter built for the upper atmosphere measured Mars shedding roughly 100 grams of gas per second to the solar wind — and about ten times that during solar storms.

A computer-rendered close view of Mars. The planet's rusty, faintly cratered curve sweeps from the upper left corner down to the lower right and fills most of the frame, with a bright golden arc of light hugging its edge. Beyond the edge, a dark red wispy haze spreads through the black space above.
A frame from a NASA Goddard animation of Mars and its upper atmosphere, issued with the mission's finding on hydrogen escape and water loss from the planet. MAVEN, which reached Mars orbit on 21 September 2014, was the first mission devoted to understanding that upper atmosphere. · Image: NASA/GSFC

MAVEN launched on 18 November 2013 to study the top of the atmosphere and its boundary with the solar wind. The United States government shut down on 1 October 2013, seven weeks before launch and 26 months before the next window; work resumed after the mission was declared an exception, needed as a rover relay.

It arrived on 21 September 2014 into a deliberately stretched orbit, from about 150 kilometres out past 6,000, sampling the whole vertical structure of the upper atmosphere every lap. "Deep dip" campaigns took the low point to around 125 kilometres, where drag had to be managed rather than measured.

In November 2015 the team reported that Mars loses roughly 100 grams of atmosphere to space every second, and faster billions of years ago, most of it down the induced magnetotail and a smaller plume over the poles. When an interplanetary coronal mass ejection struck in March 2015, escape rose about an order of magnitude for the storm's duration.

During a solar energetic particle event MAVEN recorded diffuse auroras across much of the northern hemisphere, glowing down to about 60 kilometres, deeper than at any other planet: Mars has no global magnetic field to funnel charged particles to the poles, so they rain in everywhere at once. It also found an unexplained dust cloud between 150 and 300 kilometres up.

In 2017 the team read argon isotope ratios in the upper atmosphere as a record of cumulative loss: about two-thirds of the planet's argon is gone, and at least half a bar of carbon dioxide stripped to space. Surface pressure today is about six millibars.

MAVEN worked at Mars for eleven years, doubling as a relay for Curiosity and Perseverance. On 6 December 2025 it passed behind Mars and emerged spinning fast enough to drain its batteries, and never answered again. NASA listened for months and closed the mission on 3 June 2026, leaving surface relay to Odyssey, Mars Reconnaissance Orbiter and the Trace Gas Orbiter.