NASA Probe to Track Mars’s Missing Atmosphere

Where did the Red Planet’s carbon dioxide blanket and liquid surface water go? NASA’s Maven mission will launch next week to investigate
illustration of the Mars Maven probe

NASA/Goddard Space Flight Center

Lest we forget, getting to Mars is hard. Two thirds of the missions launched to the Red Planet never made it, and only the U.S., European Space Agency (ESA) and the Soviet Union have succeeded thus far. India is vying to join their ranks with the recently launched Mars Orbiter Mission, and NASA hopes to continue its winning streak next week, when it lofts the Maven spacecraft on a journey to trace the mystery of Mars’s missing atmosphere.

If it succeeds, Maven will join two other NASA orbiters (the Mars Reconnaissance Orbiter and Mars Odyssey) as well as ESA’s Mars Express, in circling the Red Planet, and will help relay messages from the U.S. space agency’s current and future rovers on the ground (Curiosity and Opportunity, and another rover planned to launch in 2020) back to Earth. This vital job was the main reason that NASA spared Maven when work on all other prelaunch NASA missions halted during the U.S. government shutdown last month. If technicians had not continued preparing the probe, it might have missed its three-week launch window toward Mars. “As a program, we recognized a risk to the agency of not only missing the science that [Maven] was poised to do, but also of not having a long-lived enough asset” to continue relaying communications from Mars rovers back to Earth, Lisa May, Maven program executive at NASA’s Headquarters, said during a press conference October 28 previewing the mission.

While it plays telephone operator, Maven will also delve into complex questions about the thin and disappearing atmosphere at Mars. Evidence uncovered by previous missions suggests Mars used to have a drastically different climate, with a thicker carbon dioxide atmosphere that helped insulate and pressurize a warmer surface carved by liquid running water. This atmosphere has largely dissipated over time, and Mars’s surface is now too cold for liquid water. “The mystery of what happened to Mars’s atmosphere is indeed a mystery yet to be solved,” said John Grunsfeld, the associate administrator for NASA’s Science Mission Directorate, “Maven is designed to do just that.”

A leading suspect behind the disappearing act is the sun, which bombards Mars and the other inner planets with radiation and charged particles in its “solar wind.” These particles are thought to sweep away atmospheric gas, molecule by molecule, gradually depleting it over time. Earth, too, is showered with solar wind, but our planet’s global magnetic field keeps the worst of it at bay. Mars used to have a magnetic field, but lost it billions of years ago—perhaps because ancient asteroid impacts shut down convection in its core—so the planet is exposed to the full force of the sun’s fury. “Our overriding science question is, ‘Did the sun strip off the atmosphere? Is that the major process responsible for the change in climate?’” says Maven’s principal investigator Bruce Jakosky of the University of Colorado at Boulder Laboratory for Atmospheric and Space Physics. Among Maven’s eight science instruments are six tools to analyze the solar wind at Mars and study the interactions of charged particles in the planet’s atmosphere.

The $671-million spacecraft also carries an ultraviolet spectrograph to map global trends in the planet’s thin upper atmosphere as well as an instrument to detect neutral gas—especially a chemical called deuterium. This heavy version of hydrogen is more common than regular hydrogen in Mars’s atmosphere because its greater mass makes it harder to float away from the planet’s gravitational pull. Scientists plan to compare Maven’s measurements of the current ratio of deuterium with hydrogen in the atmosphere to the ratio bound up in eons-old rocks on the Martian surface. These observations should reveal to how much hydrogen has been lost over time. “The hydrogen gets at the question of ‘Where did the water go?’” Jakosky says. “We’re trying to measure the full range of processes, the full range of cause and effect” involved in Mars’s climate change, he adds.

One instrument Maven lacks is a detector for methane, a chemical that could indicate the presence of microbial life. Earth-based telescopes and Mars orbiters have seen signs of methane at the Red Planet since 1999, but in September NASA’s Curiosity rover found no evidence for the gas, dampening hopes for present-day Martian life. NASA considered a methane detector for Maven but ultimately rejected it. “We had to leave that off to stay focused and stay within our resources,” Jakosky said during the press conference. India’s Mars Orbiter Mission will be capable of detecting methane, however. “We have had some discussions with the Indian mission,” Jakosky said. “At the point where we’re both in orbit collecting data, we do plan to collaborate and work with the data jointly.” Both vehicles are due to arrive next September, if all goes well.

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