On May 4, three and a half years into its mission, NASA’s InSight lander recorded the largest “earthquake” ever detected. The magnitude 5.0 quake was nearly 10 times stronger than the Red Planet’s previous record-breaking quake, hitting the upper limits of what NASA geologists had dreamed of finding on Mars. And that could turn out to be the swan song of the mission.
Less than two weeks after the record-breaking earthquake, NASA announced that InSight was in trouble, not from seismic activity, but from a layer of rusty-red dust that was slowly building up on its solar panels. Barring a fortuitous gust of wind blowing the dust away, the lander could be dead in early to mid-July. Now NASA engineers are scrambling to collect as much data as possible during InSight’s remaining time.
InSight has faced a host of unique challenges since its crash on Mars in late 2018. On Earth, geologists typically collect earthquake data using suites of seismic stations strategically placed in geologically active areas and solidly anchored in the ground to shelter them from excessive vibrations caused by wind, water and people walking around.
By contrast, “on Mars, we only have one seismometer,” says Ingrid Daubar, a planetary scientist at Brown University who helped plan InSight’s goals. It is therefore difficult to determine where exactly an earthquake comes from.
In addition to being limited to a single station, most of InSight’s equipment sits above ground because burying it would be exceptionally difficult. “You can’t send a backhoe to Mars,” says Suzan van der Lee, a seismologist at Northwestern University who was not on the InSight mission. Even with its wind and sun shields deployed, InSight’s equipment is still likely to pick up noise from natural phenomena that land-based seismometers simply don’t have to deal with.
The mission was equipped with an underground instrument, but unfortunately it did not work as expected. InSight’s set of heat fluxes and physical properties, affectionately nicknamed “the mole”, was intended to measure the amount of heat rising from deep within the earth’s crust. But when the mole was deployed in 2019, it immediately ran into trouble. Mars’ soil turned out to have less friction than InSight geologists predicted, rendering the probe unable to reach its predicted depth of about five meters. Instead, the mole managed to penetrate just five centimeters into the Martian surface.
“Not being able to get this heat flux measurement was probably the biggest disappointment of the mission,” InSight principal investigator Bruce Banerdt said at a May 17 press conference.
Nevertheless, InSight has given geologists an unprecedented window into Mars’ internal activities. In fact, the mission was successful enough for NASA to greenlight a two-year extension after achieving its primary goals in late 2020. Based on data collected from more than 1,300 Marchquakes, the Scientists now have a clearer idea of the size and density of the planet’s core, which is larger and less compact than previously thought. And they learned a lot about the mechanisms that govern the geological activity of Mars.
Earthquakes on rocky celestial bodies can be triggered by a number of different things: fault lines, volcanoes, meteor impacts, and even influence from other planets. “Many moonquakes are due to gravitational forces imposed by the Earth,” van der Lee explains.
About 90% of earthquakes on Earth are produced by the movement of tectonic plates, massive slabs of the planet’s lithosphere that slide over the semi-solid asthenosphere layer and sometimes collide with each other. Earth’s tectonic plates are quite active, especially around certain fault lines (think San Andreas). Pressure builds up under the plates along these areas as they grind together and periodically releases in the form of tremors.
However, the lithosphere of Mars does not have these distinct plate boundaries. “Instead of having multiple tectonic plates, it’s kind of a thick plate,” says Daubar. This means that, rather than being the result of plate tectonic shifting or grinding, the Red Planet’s seismic activity must be coming from some other mechanism. Scientists now suspect that most Mars quakes are triggered by the gradual cooling of the planet’s interior, which eons ago was hot enough to blow up towering supervolcanoes such as Olympus Mons, the tallest and the largest peak in the entire solar system. As the ground around these volcanic hotspots settles on geologic timescales, the Martian crust is cracking like a fallen blast, sending shock waves rippling through the planet.
Such activity likely caused the 5.0 magnitude earthquake. Without dramatic tectonic plate movements, planetary scientists don’t believe quakes can match earthquakes in intensity, which regularly register magnitude 7.0 and above.
Despite InSight’s successful studies, geologists still have lingering questions about Mars’ seismic activity. For example, earthquakes are sometimes shallow enough to generate undulating “roller coaster” waves on the surface of our planet. “We haven’t really seen them on Mars yet,” van der Lee says. “And it’s not entirely clear why.” And the exact origin of the recent massive earthquake is still unclear.
But most likely, those questions will have to wait at least until — or if — the European Space Agency’s ExoMars rover mission lifts off. InSight’s likely expiration date is approaching as its solar panels fail due to dust. The experiment normally requires 5,000 watt-hours per Martian day to run. “Today we’re about a tenth of that available power,” Kathya Zamora Garcia, a system engineer at NASA’s Jet Propulsion and deputy project manager for InSight, said at the May 17 press conference. ExoMars, which was due to take off later this year, is also equipped with a seismometer. Unfortunately, the project was anchored indefinitely by Russia’s invasion of Ukraine, leaving InSight without a clear successor.
It’s possible that a swirling dust devil – a common Martian phenomenon – is coming to clean the panels. Such events have kept NASA’s Spirit and Opportunity rovers alive for years beyond their expected three-month lifespan. However, this possibility seems increasingly remote. “Maybe we’ll get a nice thick dust devil and we’ll have enough power to keep going for a while,” Daubar says. “But we haven’t seen a lot of that yet.”
Until then, the InSight team plans to continue extracting as much seismic data from their lander as possible. And researchers will continue to study all of the sightings it has already returned for years to come. Daubar sees it as a bittersweet end and an exciting beginning. “For planetary scientists, that’s where it’s at.”