High above the surface of Mars, winds circulate from dayside
to night, and the air undulates as it passes over mountains and valleys far
below, a new study shows.

These insights come courtesy of NASA’s MAVEN spacecraft,
which now has provided the first
detailed maps of winds in the Martian thermosphere
, one of the highest
layers of the planet’s atmosphere. The data, described in the Dec. 13 Science,
could help researchers better understand how the Red Planet’s climate has
changed over time by looking into how Mars’ atmosphere bleeds into space.

“Looking at how gas circulates in that layer allows us to
better understand the rate at which the atmosphere is being lost and the way it’s
being lost,” says study author Mehdi Benna, a planetary scientist at NASA’s
Goddard Space Flight Center in Greenbelt, Md.

Wind movement in Mars’ thermosphere is much simpler than on
Earth, data from the orbiter show. A single circulating flow persists from
season to season, continually moving air from the planet’s dayside to its nightside,
whereas on Earth there are multiple flow patterns at any one time. “Oceans on
Earth complicate the circulation patterns,” Benna says. “Mars doesn’t have all
that.”

The spacecraft, which
arrived at Mars in 2014
, also recorded waves in the thermosphere generated
by winds near the ground diverting around mountains and canyons (SN: 9/22/14).
“When the spacecraft is flying over a mountain, we can see the wind shifting to
accommodate the presence of that mountain 200 kilometers below,” Benna says.
“MAVEN doesn’t carry [traditional] cameras … but we can see a picture of the
topography in the winds.”

In all, the researchers tracked winds for one and a half
Martian years. While it’s still too early to say precisely what this all means
for the trickle of Mars’ atmosphere into space, Benna says that these maps lay
the foundation for improved computer simulations that will help researchers
figure it out.