NASA’s MAVEN spacecraft revealed how Mars lost its atmosphere and water

What is the achilles’ heel of Mars? MAVEN found out.

NASA launched the MAVEN mission to Mars in 2013, around the same time as India’s popular Mangalyaan spacecraft, and entered martian orbit the year after. In the six years since, MAVEN has been unravelling how exactly Mars loses its atmosphere to space, providing clues on how and when the planet lost its water.

Artist’s concept of the NASA MAVEN spacecraft orbiting Mars. Credit: NASA

Why NASA launched MAVEN?

Earth’s magnetic field protects us from high-energy particles coming from the Sun by deflecting them away from the planet, avoiding our atmosphere from being stripped away. Mars doesn’t have a magnetic field of its own, so solar radiation strikes its atmosphere directly, knocking atoms off into space. Scientists think this is how Mars lost most of its once dense atmosphere 3 billion years ago, turning a warm, watery planet into a chilly, dry desert world.

This artist’s concept depicts the cold, dry Mars today (left) versus the early warm martian environment (right), believed to contain liquid water. Credit: NASA

Without much of an atmosphere, Mars lost its surface water, essential for life as we know it, which once flowed freely on Mars. This is evident in features resembling dry riverbeds and minerals that only form in the presence of liquid water. MAVEN is studying Mars’ atmosphere to help us understand exactly what happened in Mars’ past. This gives us clues about possible past life there, and what planetary processes make Earth a haven for life.

MAVEN is part of NASA’s Mars Exploration Program, an unprecedented, multi-decade campaign to comprehensively understand Mars and its suitability to host past or present life. Within just weeks of arriving at Mars, MAVEN observed oxygen, carbon and hydrogen escaping from the planet’s atmosphere into space. These atoms were once a part of carbon dioxide and water vapor molecules near the surface.

WHAT MAVEN SEES: NASA’s MAVEN spacecraft observes Mars with an ultraviolet instrument that allows it to detect carbon (left), oxygen (center) and hydrogen (right) escaping from the planet’s atmosphere. The outline of the planet itself is drawn with a red circle. The hydrogen gas in particular form extend up to thousands of kilometers above the planet’s surface. Credits: University of Colorado/NASA

MAVEN found that Mars’ atmospheric loss is primarily driven by the Sun. The Sun emits a stream of hot, highly energetic particles collectively known as the solar wind. When this solar wind hits the unprotected Martian atmosphere, it imparts energy to atmospheric atoms and molecules, giving them enough velocity to escape martian gravity. MAVEN learned that the solar wind penetrates more deeply into Mars’ atmosphere than previously thought.

In this artist’s concept, the solar wind directly interacts with Mars’ upper atmosphere, but is deflected by Earth’s protective global magnetic field. Credit: NASA

Because of its egg-shaped orbit, Mars is closer to the Sun at some points than others. MAVEN saw that Mars lost 10 times more hydrogen at the nearest points than at its farthest. This is due to Mars receiving about 40% more sunlight and solar wind there, as well as increased summer heat kicking off gases from near the surface to the upper atmosphere, where the atmospheric loss strengthens.

Aurorae on Mars

Aurorae on Earth are caused by energetic charged particles from space crashing down into the atmosphere along Earth’s magnetic field lines, causing gases to glow near the poles. Since Mars has no strong magnetic field, the solar wind penetrates deeper and causes bright, planet-wide aurorae.

MAVEN orbiter captures a bright aurora on Mars during a solar storm in September 2017. The purple-white colors show the intensity of ultraviolet light on Mars’ night side before (left) and during (right) the event. Credits: University of Colorado/NASA

MAVEN’s observations helped scientists understand that increased upper atmospheric gases during summer cause enhanced atmospheric loss as well as increased auroral glow, linking the two phenomena together.

Can Mars be terraformed?

While life on Earth was taking shape and spreading over three billion years ago, Mars was rapidly losing its atmosphere and water, including carbon dioxide that would have kept the planet warm for a longer period. In fact, data from recent NASA’s Mars orbiters have pointed out Mars has so little carbon dioxide left that artificially warming the planet up to make it habitable isn’t possible with present-day technologies. This means that any liquid water introduced on Mars’ surface would evaporate and eventually escape. Sorry, would-be Martians: Mars can’t be terraformed!

MAVEN has also contributed to other aspects of martian science, like observing pristine metallic comet dust in Mars’ atmosphere after a comet flew by the planet, and detecting mirror-like plasma layers in Mars’ upper atmosphere, the same kind that causes radio interference on Earth. MAVEN created a global wind map of the planet’s upper atmosphere, a first for any planet other than Earth and saw huge clouds spanning hundreds of kilometers being formed in a matter of hours!

MAVEN also acts as a high-speed communications relay between surface spacecraft and Earth, allowing us to get more science data back from Mars than would be otherwise possible.

How MAVEN studies Mars’ atmosphere

One of MAVEN’s flagship instruments is the Imaging UltraViolet Spectrograph, or IUVS, a camera tailored to ‘see’ ultraviolet light. This helps MAVEN directly see and measure gases leaving Mars’ atmosphere since they reflect and scratter ultraviolet light. The same instrument also allows MAVEN to observe the planet-wide aurorae whose gases glow in ultraviolet.

MAVEN also detects solar wind entering Mars’ upper atmosphere using a mass spectrometer, a device that determines the elemental makeup of materials passing through it. A magnetometer on the spacecraft measures the electrical charge created when the solar wind hits atmospheric particles, which creates a weak magnetic field that accelerates the particles away from the planet.

The solar wind wraps around Mars, inducing electric currents (blue and red arrows) and subsequently a weak magnetic field around the planet. Credits: NASA/MAVEN/Cindy Starr

By continuously and extensively tracking the upper atmosphere for almost three Martian years i.e. roughly six Earth years, MAVEN has shown for the first time how exactly Mars loses its atmosphere and at what rate. MAVEN Remote Sensing Team member Justin Deighan of the University of Colorado, Boulder said:

With these maps we have the kind of complete and simultaneous coverage of Mars that is usually only possible for Earth.

In 2019, mission operators lowered MAVEN’s orbit so that it can relay data between Earth and NASA’s Perseverance rover. MAVEN has enough fuel to be operational until at least 2030, so it will be increasingly tasked with replacing communication relay responsibilities of aging orbiters like MRO and Mars Odyssey. While not conducting relay communications, MAVEN will continue to study Mars’ atmosphere.

Left: MAVEN’s orbit until 2019 for the science phase of its mission. Center: MAVEN performed a series of “deep dip” orbits approaching within about 125 kilometers of Mars, causing drag from the atmosphere to reduce its orbit. Right: Tighter post-aerobraking orbit allowing for enhanced relay communications. Credits: NASA, Kel Elkins and Dan Gallagher

Originally published at The Planetary Society.

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