Are marsquakes anything like earthquakes? NASA is about to find out.

On Earth, we call them earthquakes, and
on the moon they’re called moonquakes. On Mars^[1]? They’d be
marsquakes—except no one really knows how frequently the red planet
jiggles and shakes, or how big those marsquakes can get.

But humans could soon find out just how
much the fourth rock from the sun is rocking and rolling: NASA’s
newest Mars-exploring spacecraft, called
InSight^[2], blasted off from
California’s Vandenberg Air Force Base on Saturday at 4:05 a.m.
Pacific time, marking the first time an interplanetary probe has
launched from the West Coast. The spacecraft has since been
cruising through the solar system and is due to rendezvous with
Mars around 3 p.m. ET on November 26.

Unlike many Mars missions that have come before, InSight will
not be exploring the red planet’s surface. Instead, as the name
suggests, the spacecraft will peer deep into the Martian interior
and try to paint a picture of how this alien world works from its
core on outward, which could help us understand what’s happening on
even more distant alien worlds.

“What goes on in the interior of a planet drives the surface
geologic activity and even the atmospheric evolution,” says Suzanne
Smrekar^[3] of NASA’s Jet Propulsion
Laboratory, a deputy principal investigator for the InSight
mission. “You really need to understand the overall geological
evolution to begin to understand the habitability of planets.”

After parachuting through the Martian atmosphere, the spacecraft
will park itself in Elysium Planitia, a region selected
specifically because it’s more or less geologically unremarkable
and because it’s on the equator, where more prolonged sunshine will
be good for the solar-powered spacecraft.

“For InSight, whose primary focus is to look to the interior of
the planet, what the surface looks like where we land doesn’t
matter as much,” says Renee Weber^[4] of NASA’s Marshall Space
Flight Center.

Nowhere. Unlike the fleet of rovers that have stumbled, rolled,
and climbed their way across evaporated lakes and into craters,
InSight is staying in one place. Its job is basically to stay as
still as possible, the better to detect the motion of Mars
itself.

It’s true, seeing through a planet is tricky even for the most
insightful of spacecraft, so the lander will rely on several
instruments to peer into the Martian underground. These include a
probe that will burrow between 10 and 16 feet deep and measure heat
radiating inside the planet, as well as an extremely sensitive
seismometer, built by the French national space agency, that’s
designed to detect even the most gentle of marsquakes. (Here’s
how
governments and private companies plan to one day get humans to
Mars^[5].)

“The seismometer is so sensitive that even the motion of its
parts against the atmosphere creates noise that we want to
eliminate,” Weber says. Because of its extreme sensitivity, the
seismometer requires some hefty vacuum-sealed shielding to
eliminate vibrations caused by wind or other surface events that
can create annoying noise in the data. A leak in that vacuum
chamber delayed the spacecraft’s original launch date by 26 months.
Now, though, the team is confident this crucial instrument is ready
to ride.

After a few months on Mars, InSight will drop the seismometer
directly onto the planet’s surface, a configuration that (the team
hopes) will eliminate some of the problems that confounded a
similar experiment on the ‘70s-era Viking landers. Then, if all
goes well, the spacecraft and its instruments will keep track of
the planet’s beats and spasms for two Earth years, or the
equivalent of roughly one Martian year.

On Earth, quakes are caused by tectonic activity, most of which
are produced when gigantic plates in Earth’s crust go slipping,
sliding, or diving beneath one another, or by magmatic activity
associated with volcanoes. But unlike Earth, Mars doesn’t have a
crust broken into plates (or at least there’s no evidence for such
a thing).

“We have no volcanic system on the Earth that has lasted for
billions of years,” Smrekar says.

(The moon, which also lacks tectonic plates, still experiences
moonquakes. Mostly these are the result of tidal forces yanking on
the moon, but some are caused by meteorite impacts.)

No one knows. One of the mission’s primary goals is to figure
out how tectonically active Mars is—how often the planet wiggles,
how big those tremors are, and where they come from. As with the
moon, the team expects the lander to sense vibrations produced by
meteorite impacts, as well as quakes caused as the planet cools,
and maybe even the rumblings of distant magma. (Find out why
scienstists think Mars has abundant water deep inside^[6].)

“About a thousand miles away, there’s been volcanism within the
last one to 10 million years,” Smrekar says. “In geological terms,
that’s yesterday.”

Marsquakes will be measured in magnitude, as Earth’s are,
although the way a magnitude 5 quake feels on Mars won’t
necessarily be the same as on our home world because of differing
gravity and rock composition.

“We think that the seismicity of Mars will probably lie
somewhere between Earth and the moon,” Weber says.

You wouldn’t want to build a house in a Martian lava tube and
then have that tube collapse on your head in a marsquake, would
you? No. But that’s a scenario for the future.

For now, knowing how frequently and at what magnitude Mars
shakes will not only reveal how tectonically active the planet is,
but will also offer clues about how it evolved. As well, marsquakes
will allow the team to directly map the planet’s insides. As they
travel, seismic waves move through materials of differing density
and composition, sometimes being bounced off boundaries between
layers, and they carry information about what they’ve moved through
before reaching the seismometer.

“Once you are able to locate the event, then you can learn what
the structure of the planet is along that wave path,” Weber
explains. “Really, all we need once we get there is just to record
some quakes!”

By snaring enough of these waves and disentangling the
information they carry, scientists will be able to figure out how
thick the Martian crust is, whether the planet’s mantle is layered,
the size of its core, and whether that core is liquid or solid. On
Mars, those layers haven’t been mixed by convection and plate
tectonics as on Earth, so scientists expect the planet’s interior
to retain a record of its early history and composition.

“One of the big questions that we’re trying to understand better
is how a planet goes from being molten to having the interior
layers that all rocky bodies have,” Smrekar says.

Kind of crazy, right? There’s also a chance that data from
InSight could be correlated with a Mars-orbiting spacecraft that’s
sniffing for methane in the planet’s atmosphere. Long a conundrum,
Martian methane is suspected to be geologically produced—although
there’s a chance it could be biologically produced as well. If that
spacecraft, called the ExoMars Trace
Gas Orbiter^[7], detects methane in
areas where InSight detects recent tectonic activity, it could
strengthen the case for the gas’s non-biological origin, Smrekar
says.

The spacecraft is also carrying several cameras, a radio science
experiment, a laser retroreflector, some meteorological sensors,
and a few other gadgets. And it will be trailed by a pair
of CubeSats^[8] that will relay
information as InSight enters the Martian atmosphere, descends, and
lands.

There’s even the tantalizing possibility of an app that will let
Earthlings know when the red planet next door is quaking, so all
those in training to live on Mars can practice ducking and
covering.