On Earth, we call them earthquakes, and on the moon they’re called moonquakes. On Mars? 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, 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 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.”
Where is InSight landing?
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 of NASA’s Marshall Space Flight Center.
OK. Where’s it going after that?
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.
How does one simply … peer into a planet?
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.)
“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.
So about marsquakes—how do they work?
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).
Even so, it does have tectonic activity, meaning that there are faults where the Martian crust is buckling or folding, and plumes of hot material that rise up from the interior are responsible for building some of the biggest volcanoes in the solar system. Those, the Tharsis volcanoes, have been around for billions of years. (See the surprising ways Mars has changed over three billion years with our interactive red planet.)
“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.)
How big are marsquakes?
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.)
“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.
Why do we care about marsquakes?
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.
That sounds like a lot for one spacecraft to do!
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, 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 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.