NASA InSight Lander has detected 500 earthquakes on Mars, but without magnitude 4

NASA’s InSight lander has observed more than 500 earthquakes on Mars since it landed on the red planet in 2018. But there is a glaring hole in its catalog: the lander has not yet detected large noises.

“We would have expected a few magnitude 4 and maybe even magnitude 5 events right now, given the number of smaller earthquakes,” Bruce Banerdt, chief investigator for InSight, told Insider.

Instead, most of the quakes were so calm that the average Californian would not have even noticed them. The four largest earthquakes on Mars The InSight seismometer felt ranged from 3.1 to 3.6.

So seismologists on Mars are starting to scratch their heads. Either the InSight team just got unlucky, or Mars can’t make big earthquakes at all. If it’s the latter, Banerdt said, “we don’t really know what that means yet.”

The reason scientists are so interested in the motion of Mars is that measuring earthquakes can reveal what the inside of the planet looks like. So far, Insight readings have indicated that Mars may have Earth-like layers deep beneath its shell, which are wrapped in a moon-like outer shell that has been struck by asteroids.

NASA / JPL-Caltech

But really big earthquakes would help scientists see deep into the Martian core, which could provide clues about how the planet was born and how it evolved over time. A better understanding of the interior of Mars could be crucial in our efforts to find other worlds that could host life.

“Looking at the core of Mars and looking at the crust of Mars and understanding that they haven’t changed much in the last 4.5 billion years, we can take a look at what the Earth might have looked like very early on.” Banerdt said. “Mars helps us understand how formed the rocky planets are and how they evolve in general.”

Banerdt and his team hope to figure out why they don’t see large earthquakes on Mars – either to know how to look for them better in a future mission, or to be able to identify what’s happening to the Martian interior that makes earthquakes. major so rarely.

Earthquake Mars indicates an Earth-like crust with a moon-like crust

NASA / JPL-Caltech / ETH Zurich / Van Driel

Listening to the earthquakes of a planet is like doing a CAT scan. When doctors do this type of scan, a machine sends X-rays through your body, then analyzes how the waves return at different times and in different directions. This allows them to “put together the 3D geometry of what’s going on inside your body,” Banerdt said.

With InSight, he continued, we do the same thing with a planet, using earthquakes on Mars as “radiation waves,” and the seismometer is the detector.

Scientists used to believe that Mars must have a crust like that of Earth, which was smoothed by geological activity, such as the movement of tectonic plates and the boiling of molten magma from below. But the InSight seismometer painted a more nuanced picture.

“It’s somewhere between the moon and the earth in the way it transmits seismic waves,” Banerdt said.

On the moon, the crust was broken due to the impact of the asteroid, which gives seismic waves more cracks and surfaces to jump. It’s like taking a “drunk walk,” Banerdt said, making the earthquakes last for hours.

NASA / Eugene Cernan

On Earth, seismic waves do not reverberate as much, so they weaken rapidly. The moisture in the crust of our planet also allows it to absorb some of their energy. As a result, earthquakes usually last only a few seconds, although really big ones can last a few minutes.

Meanwhile, earthquakes on Mars appear to generally last between 10 and 40 minutes.

The first few hundred tremors that InSight brought to Mars behaved similarly to those on the moon. But because they were so small, they only allowed scientists to analyze the structure of the top layer of the crust. The handful of larger earthquakes – which gave the InSight team a look at the deeper layers – acted more like earthquakes.

“I think maybe Mars has an outer layer that’s pretty lunar,” Banerdt said. “It’s pretty far from the impacts. But deeper in the planet, in the mantle, it looks like it could be more like Earth.”

The mystery of the great missing

NASA / JPL-Caltech / Univ. from Arizona

InSight Mars earthquakes follow a similar pattern to earthquakes: the larger the magnitude, the rarer the earthquake.

“You get fewer and fewer earthquakes as you get more and more numbers and some kind of exponential law follows,” Banerdt said.

So far, the tail end of that exponential graph is missing. It could just be a quiet time on Mars – planets can have spells with a lot of seismic activity and dry periods without major earthquakes. But Banerdt suspects InSight data indicates a higher trend.

“There seem to be fewer large earthquakes on Mars, compared to the number of small earthquakes, than we would expect. It’s a little puzzling,” he said. “We’re still trying to figure out what the explanation might be.”

NASA may simply not have chosen a good place to hunt big earthquakes. On Earth, there are a lot of areas that never see major earthquakes. Or maybe Mars has never shaken so much.

“It could be related to gravity, it could be related to the thickness of the fragile layer, it could be related to a lot of things. But right now, we really don’t have a handle on that,” Banerdt said. “It’s an ongoing field of research.”

InSight is about to hibernate through the “optimal” earthquake time

NASA / JPL-Caltech

The longer InSight waits and listens, the more likely we are to catch a big earthquake. Unfortunately, the lander is about to take a break for a few weeks during the peak of listening to the earthquake.

That’s because Elysium Planitia, where InSight landed, surprised NASA with its lack of wind. There is some wind – enough to drown out the seismic noise of distant earthquakes. But it’s not enough to keep the red Martian dust on InSight’s solar panels.

Now, the Martian winter is settling in and a thick layer of dust is taxing the robot’s energy production. So NASA decided to hibernate InSight. In February, the lander began gradually shutting down its scientific instruments, keeping its power to warm itself.

In June, NASA expects to completely shut down InSight’s scientific operations until Mars returns to the sun in July.

The seismometer is still in operation, but Banerdt expects it to shut down in a month or so. It will be in the middle of the “optimal” time to detect earthquakes on Mars, he said, as the winds die in the depths of winter. The low wind allows the seismometer to catch distant earthquakes with less interference.

“We hope to keep the seismometer as long as possible, then turn it on again – you know, after we’ve spent this time on low power – turn it on as fast as we can,” Banerdt said. “But we’ll probably miss some things between them.”

If InSight survives its energy shortage, the seismometer could continue to listen for earthquakes until 2022.