On May 4, three and a half years after its mission, NASA’s InSight lander recorded the largest “tremor” ever detected. A magnitude 5.0 earthquake was almost 10 times stronger than the previous record shock on the Red Planet, reaching the upper limit of what NASA geologists dreamed of finding on Mars. And it could turn out to be a swan song mission.
Less than two weeks after the record-breaking earthquake, NASA announced that InSight was in trouble – not because of seismic activity, but because of the slow build-up of a layer of red rust dust on solar panels. Except for an accidental gust of wind to clear the dust, the planter may be dead by early to mid-July. Now NASA engineers are fussing to gather as much data as possible for the time left by InSight.
Since then, InSight has faced many unique challenges committing the fall of the planet on Mars in late 2018. On Earth, geologists typically collect earthquake data using sets of strategically located seismic stations that are located in geologically active areas and firmly anchored in the ground to protect them from excessive vibrations caused by wind, water, and people.
In contrast, “we only have one seismometer on Mars,” said Ingrid Daubar, a planetary scientist at Brown University who helped plan InSight’s goals. This makes it difficult to pinpoint exactly where the earthquake comes from.
In addition to limiting one station, most InSight equipment is above ground because burying it would be extremely difficult. “You can’t send an excavator to Mars,” said Susan van der Lee, a seismologist at Northwestern University who was not involved in the InSight mission. Even with deployed wind and sun shields, InSight equipment still tends to pick up noise from natural phenomena that terrestrial seismometers simply don’t have to deal with.
The mission was equipped with one underground tool, but unfortunately he did not act as planned. The InSight package of heat fluxes and physical properties, affectionately known as the “mole”, was designed to measure the amount of heat emanating from beneath the planet’s crust. But when the mole was deployed in 2019, he was immediately faced with a problem. It turned out that the soil of Mars has less friction than planned by InSight geologists, as a result of which the probe was unable to reach the estimated depth of about five meters. Instead, the mole managed to penetrate only five inches into the surface of Mars.
“The inability to obtain this heat flux measurement was probably the mission’s biggest disappointment,” InSight chief researcher Bruce Banerdt told a news conference on May 17.
However, InSight gave geologists an unprecedented window in the internal events of Mars. In fact, the mission was successful enough for NASA to give the green permission for a two-year extension after it completed its major targets in late 2020. Based on data collected from more than 1,300 sea tremors, scientists now a clearer idea the size and density of the planet’s core, which is more and less compact than previously thought. And they learned a huge amount about the mechanisms that control the geological activity of Mars.
Earthquakes on rocky celestial bodies can be caused by a number of different things: fault lines, volcanoes, meteor strikes and even the influence of other planets. “A lot of earthquakes are due to gravitational forces acting on the Earth,” says van der Lee.
About 90 percent of the earthquakes on Earth are caused by the movement of tectonic plates, massive plates of the planet’s lithosphere, which slide over the top of the semi-solid layer of the asthenosphere and occasionally collide with each other. The Earth’s tectonic plates are quite active, especially around some fault lines (think San Andreas). The pressure builds up under the plates along these areas when they are crushed together and periodically erupts in the form of tremors.
However, the lithosphere of Mars lacks these clear plate boundaries. “Instead of having multiple tectonic plates, it’s one kind of thick plate,” Daubar explains. This means that the seismic activity of the Red Planet must arise as a result of some other mechanism and not as a result of sliding or grinding plates. Scientists now suspect that most of the shocks are causing a gradual cooling of the planet’s interior, which eons ago were hot enough to erupt high supervolcanoes such as Olympus – the highest and largest peak in the entire solar system. As the earth around these volcanic hotspots settles on a geological time scale, the Martian crust cracks like a falling souffle, sending shock waves sweeping across the planet.
Such activity probably caused a magnitude 5.0 earthquake. Without the sharp movements of tectonic plates, planetary scientists do not think that earthquakes can coincide with the intensity of earthquakes, which are regularly recorded with a magnitude of 7.0 and above.
Despite successful InSight studies, geologists still have protracted questions about the seismic activity of Mars. For example, earthquakes are sometimes small enough to generate wave-like “roller coaster” waves on the surface of our planet. “We haven’t seen them on Mars yet,” says van der Lee. “And it’s not entirely clear why.” And where exactly the recent powerful push came from is still unclear.
But most likely, these issues will have to wait, at least until – or when – the mission of the rover ExoMars of the European Space Agency to take off. The probable shelf life of InSight is approaching as the solar panels fail due to dust. The experiment typically requires 5,000 watt-hours on a Martian day. “Today we are about one-tenth of the available capacity,” said NASA Jet Propulsion Systems Engineer and InSight Deputy Project Manager Kathy Zamora Garcia at a news conference on May 17. ExoMars, which was due to take off later this year, is also equipped with a seismometer. Unfortunately, the project was uploaded indefinitely due to Russia’s invasion of Ukraineleaving InSight without a clear successor.
It is possible that the devil, spinning dust – a common Martian phenomenon – will come and take down the panels. Such events have been supported by NASA Spirit and Opportunity spacecraft for many years after their planned three-month lifespan. However, this possibility seems more and more remote. “Maybe we’ll get a nice thick dusty devil, and we’ll have enough strength to keep going for a while,” Daubar says. “But we haven’t seen much of it yet.”
Until then, the InSight team plans to continue squeezing as much seismic data as possible from its landing module. And researchers will continue to study all the observations he has already sent back over the years. Daubar sees in this a bitter end and an exciting beginning together. “For planetary scientists, this is the place.”