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[ music ]

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Narrator: NASA's newest Mars spacecraft, MAVEN, is currently on a mission

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to determine how Mars lost its early atmosphere, and with it, its water.

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Jakosky: The questions that MAVEN is trying to answer deal with the history of the Martian climate.

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From the previous missions we have a lot of evidence that that climate has changed over time,

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that early Mars was warmer, wetter than present-day Mars.

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What we're trying to answer with MAVEN is, "Where did all that water go?"

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"Where did the carbon dioxide from an early thick atmosphere go?" And we're doing this by studying the top of the atmosphere.

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Since we are the first mission really looking at all pieces of the puzzle on the upper atmosphere,

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almost everything we're seeing and how it relates to everything else is brand new.

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As an example, one of the things we measured very early in the mission, right after we went into orbit,

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before we even got into our final science mapping orbit, was the distribution of hydrogen,

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oxygen, and carbon as a cloud surrounding the planet, the very extended upper atmosphere.

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Narrator: In this ultraviolet image, carbon and oxygen cling tightly to Mars, while hydrogen, the lightest element, extends well above the planet.

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Understanding the escape of hydrogen is important, because hydrogen is the primary ingredient in water.

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While previous Mars orbiters have peered down at the planet's surface,

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MAVEN is spending part of its time gazing at the stars, observing the Martian atmosphere through a series of stellar occultations.

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Jakosky: The imaging ultraviolet spectrograph, the IUVS instrument,

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can determine properties of the upper atmosphere all the way down to the lower atmosphere,

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by looking at a star, as the star sets behind the planet as seen from the spacecraft.

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And by looking at the diminution, the weakening of the starlight as it sets, we can measure the composition of the upper atmosphere.

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Narrator: The relative motion of the stars allows MAVEN to look at columns of the atmosphere,

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revealing how its composition changes with altitude.

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At the same time, MAVEN's orbit passes close to the Martian polar caps, giving it north-to-south coverage of the planet.

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Mars itself rotates once a day beneath MAVEN, providing east-to-west coverage.

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This combination allows MAVEN to observe the entire atmosphere.

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Jakosky: My goal with MAVEN is to put together a data set that the Mars science community can spend the next decade or two working on.

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We're making very few measurements that have never been made at all before at Mars,

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but what we're doing is, we're making them in parts of the atmosphere where they haven't been measured,

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we're making comprehensive measurements for a full year rather than, for example with the Viking lander,

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a one-time entry, one profile. We're going to get hundreds and hundreds of profiles,

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and be able to see how the upper atmosphere responds to the changing solar conditions,

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and really put together a picture of the upper atmosphere that we haven't been able to put together before.

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[ music ]

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[ satellite beeping ]