Today, Mars is a cold, dry world
with a tenuous atmosphere only 1% as thick as Earth's.
But in the ancient past, water flowed freely across the Martian surface,
maintained by a thick, early atmosphere.
Since it first arrived at the Red Planet in September 2014,
NASA's MAVEN spacecraft has been studying how that atmosphere was lost to space -
and with it, the water. Now, as MAVEN continues its mission, we can look back on
its many remarkable discoveries during its first ten years
at Mars.
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In 2015,
MAVEN observed the solar wind eroding the Martian atmosphere.
The solar wind is a stream of electrically charged particles blowing from the sun.
MAVEN watched as ions from the Mars upper atmosphere
were accelerated by the solar wind’s, magnetic field and driven into space,
confirming that this process has deeply eroded the Martian atmosphere.
In 2017, MAVEN showed that a process called
“sputtering” has had an even greater effect on the atmosphere.
When ions from Mars get picked up by the solar wind’s magnetic field,
they can crash into neutral atoms at the top of the atmosphere,
sputtering them into space.
MAVEN measured
present-day isotopes of argon, which can be removed only by sputtering,
to determine that 65% of the noble gas has been lost over time.
This allowed scientists to estimate the escape of other gases
and determine that sputtering has been
the primary mechanism driving the atmosphere into space.
Later in 2017, MAVEN revealed
a twist in Mars's invisible magnetic tail.
When the sun's magnetic fields reach Mars, they pile up and wrap around the planet,
creating an induced magnetic field that is drawn out behind Mars
like a comet's tail.
The Martian crust also contains small pockets of its own
early magnetic field, which rotate along with the planet.
MAVEN discovered that when these two fields interact,
they put a twist in the magnetotail, confirming model predictions.
In 2018, a runaway series of dust storms
created a dust cloud so large that it enveloped the planet.
During this global dust storm, MAVEN observed an abrupt, unexpected spike
in the amount of water in the upper atmosphere.
It discovered that heating from dust storms can loft
water molecules far higher into the atmosphere than usual,
leading to a sudden surge in water lost to space.
Later in 2018, MAVEN
announced the discovery of a new type of aurora at Mars.
The mission had previously observed auroras during solar storms
after electrons from the sun struck the upper atmosphere,
causing it to glow with ultraviolet light.
MAVEN's 2018 discovery was the first observation of a Mars proton aurora.
When protons from the solar wind pick up electrons
from the Martian ionosphere, they can slip through the planet's
bow shock and plunge into its upper atmosphere, causing widespread auroras.
On Earth, proton auroras are isolated near the poles,
but on Mars they can bathe the dayside in ultraviolet radiation.
In 2019,
MAVEN produced the first map of wind currents in the Martian thermosphere,
revealing disturbances in high-altitude winds
caused by terrain features on the surface.
MAVEN sensed these disturbances as it skimmed through
the upper atmosphere,
feeling the imprint of mountains and valleys far below.
In 2020, data from MAVEN led to the creation of another new map
showing the Martian atmosphere's electric current systems for the first time.
MAVEN detected these currents indirectly,
by observing the solar wind’s magnetic field lines drape around the planet.
Mapping the electric current systems can help scientists
to better understand the forces that drive atmospheric escape.
In 2022, MAVEN watched
as the solar wind unexpectedly disappeared from Mars.
The event occurred when a fast-moving patch of the solar wind
overtook a slower-moving region, leaving a void in its wake.
In response, the Martian magnetosphere ballooned
outward by thousands of kilometers, engulfing MAVEN's orbit
and causing the solar wind to temporarily disappear from view.
In 2022 and 2023, MAVEN captured stunning ultraviolet
images of Mars when the planet was near opposite ends of its elliptical orbit.
The first image was taken when the southern hemisphere
was in summer, which coincides with Mars's closest approach to the sun.
Canyons and basins are covered with a thin haze
of ozone, indicated by a tinge of pink.
The second image was taken during northern spring,
after Mars had passed its furthest point from the sun.
White clouds hint at rapidly changing conditions in the northern polar
regions, while deep magenta signals a buildup of ozone during the frigid winter.
In 2024, MAVEN
observed the aftermath of an X-class solar flare,
the strongest type of eruption from the sun.
The flare was quickly followed by a burst of charged particles crashing into Mars,
leaving black and white streaks on images taken by NASA's Curiosity rover.
MAVEN watched from above as auroras lit up the planet
in a brilliant display of celestial fireworks.
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In its first decade at Mars, MAVEN has vastly expanded
our understanding of the Red Planet and its climate history.
Today, it continues to be a critical member
of NASA's fleet of robotic explorers, observing
the interaction between the solar wind and the Martian atmosphere
and providing a window into the ongoing evolution of Mars.
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