Scientists have been discovering new mysteries since landing the geophysics mission two years ago.
NASA’s InSight spacecraft touched down on Mars on November 26, 2018 to study the deep interior of the planet. Just over a Martian year later, the stationary lander has detected more than 480 earthquakes and collected the most complete meteorological data from any surface mission sent to Mars. The InSight spacecraft, which has struggled to dig underground to catch the planet’s temperature, has also advanced.
There was a time when the surfaces of Mars and Earth were very similar. Both were warm, humid, and surrounded by thick atmospheres. But 3 or 4 billion years ago, these two worlds took different paths. The mission of InSight (short for Inner Exploration through Seismic Research, Geodesy, and Heat Transport) has been to help scientists compare the Earth to its rusty brother. Studying what the depths of Mars are made of, how this material is layered, and how quickly heat drains could help scientists better understand how a planet’s starting materials make it more or less likely to support life.
While there’s more science to come from InSight, here are three findings about our red neighbor in the sky.
Weak rumors are the norm
The InSight seismometer, provided by the French space agency Center National d’Études Spatiales (CNES), is sensitive enough to detect slight rumors over long distances. But it was not until April 2019 that seismologists from the Earthquake Service, coordinated by ETH Zurich, detected its first earthquake. Since then, Mars has more than made up for lost time by shaking frequently, albeit gently, with no earthquakes larger than magnitude 3.7.
The lack of earthquakes larger than magnitude 4 represents a mystery, given the frequency with which the red planet shakes due to smaller earthquakes.
“It’s a little surprising that we haven’t seen any major events,” said seismologist Mark Panning of NASA’s Jet Propulsion Laboratory in Southern California, which runs the InSight mission. “It could be that he’s telling us something about Mars or that he’s telling us something about luck.”
In other words, it could be that Mars is more static than expected, or that InSight will land in a particularly quiet period.
Seismologists will have to keep patiently waiting for the largest earthquakes to study deep layers under the crust. “Sometimes you get great flashes of amazing information, but most of the time you’re testing out what nature has to say to you,” said Bruce Banerdt, principal investigator of JPL’s InSight. “It’s more like trying to follow a trail of tricky clues than presenting the answers in a very well-wrapped package.”
The wind can hide tremors
Once InSight began detecting earthquakes, they became so regular that at one point they happened every day. Then, in late June of this year, the detections essentially stopped. Since then, only five earthquakes have been detected, all since September.
Scientists believe that the wind on Mars is responsible for these seismic periods: the planet entered the windiest season of the Martian year around June. The mission knew the winds could affect InSight’s sensitive seismometer, which is equipped with a wind shield and dome. But the wind still shakes the earth and creates literal noises that cover earthquakes. This could also have contributed to what appears to be the long seismic silence before the first InSight earthquake, as the spacecraft landed while a regional dust storm was setting in.
“Before landing, we had to guess how the wind would affect surface vibrations,” Banerdt said. “Because we work with much smaller events than we would pay attention to on Earth, we find that we need to pay much more attention to the wind.”
Surface waves are missing
All earthquakes have two sets of body waves, which are waves that travel through the interior of the planet: primary waves (P waves) and secondary waves (S waves). They also roll along the top of the crust as part of a third category, called surface waves.
On Earth, seismologists use surface waves to learn more about the planet’s internal structure. Before reaching Mars, InSight seismologists expected these waves to offer views as deep as about 400 kilometers below the surface, toward a sub-crustal layer called the mantle. But Mars continues to offer mysteries: despite hundreds of earthquakes, none have included surface waves.
“It’s not entirely unheard of to have earthquakes without surface waves, but it’s been a surprise,” Panning said. “For example, you can’t see surface waves on the Moon. But that’s because the Moon has a lot more scattering than Mars.”
The dry lunar crust fractures more than Earth and Mars, causing seismic waves to bounce around a more diffuse pattern that can last more than an hour. The lack of surface waves on Mars may be related to an extensive fracture in the 10 kilometers above InSight. It could also mean that earthquakes detected by InSight come from the depths of the planet, as they would not produce strong surface waves.
Of course, unraveling these mysteries is a matter of science, and there are more things to come with InSight.
Learn more about the mission
JPL manages InSight for the direction of NASA’s science mission. InSight is part of NASA’s Discovery program, managed by the agency’s Marshall Space Flight Center in Huntsville, Alabama. Lockheed Martin Space of Denver built the InSight spacecraft, including its cruise stage and lander, and supports spacecraft operations for the mission.
Several European partners, including the National Center for Space Studies (CNES) in France and the German Aerospace Center (DLR), support the InSight mission. CNES provided the Seismic Experiment for Interior Structure (SEIS) instrument to NASA, with the principal investigator from the IPGP (Institut de Physique du Globe de Paris). IPGP made significant contributions to SIX; the Max Planck Solar System Research Institute (MPS) in Germany; the Swiss Federal Institute of Technology (ETH Zurich) in Switzerland; Imperial College London and Oxford University in the United Kingdom; and JPL. DLR provided the heat flux package and physical properties (HP3), with important contributions from the Center for Space Research (CBK) of the Polish Academy of Sciences and Astronika in Poland. The Spanish Center for Astrobiology (CAB) supplied temperature and wind sensors.
News media contacts
Andrew Good
Jet Propulsion Laboratory, Pasadena, California.
818-393-2433
[email protected]
Alana Johnson / Gray Hautaluoma
NASA Headquarters, Washington
202-672-4780 / 202-358-0668
[email protected] / [email protected]