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When the Perseverance rover lands on Mars on Thursday, another NASA spacecraft already there will listen for the thudding that will occur when the newcomer arrives.
The hope is that these muffled noises will create enough jerks to be detected by InSight, a stationary NASA probe that arrived in 2018 to listen to earthquakes with an extremely sensitive seismometer. The InSight lander sits over 2,000 miles east of where Perseverance is to land.
“We have a reasonable chance to see it,” said Benjamin Fernando, a graduate student at the University of Oxford in England and a member of the InSight science team.
Unless something goes wrong, any seismic signals InSight might hear will not emanate from the rover itself. Perseverance should be lowered to the surface of a hovering crane, gently hitting the ground at less than 2 miles per hour.
Instead, scientists will sift through InSight’s seismic data for signs of impact from two 170-pound metallic tungsten blocks that helped keep Perseverance in a stable and balanced rotation during its 300-million-mile journey. kilometers from Earth. At an altitude of 900 miles above Mars, they will be dropped like debris, and without parachutes or retrorockets to slow them down, they will then slam into the surface at around 9,000 mph.
“This tremendous speed means they will create a pretty big crater,” Fernando said. In 2012, similar tungsten blocks from the Curiosity rover, which are almost of the same design as Perseverance, left scars visible from orbit.
Arriving at a shallow 10-degree angle, the impact of the blocks will be to the east, which should create a splash of seismic energy toward InSight that would increase the chances of detecting vibrations.
If the impact waves are detected, it will not be just a technical feat. The data could help shed light on the structure of the crust of Mars.
The main purpose of the seismometer on InSight is to record marsquakes, and the spacecraft has so far recorded more than 400 such tremors. Scientists also expected InSight to detect jerks caused by space rocks occasionally crashing into Mars.
But so far, the number of recorded meteor strikes is zero. Or at least, there aren’t any tremors that scientists could confidently conclude were generated by such collisions. The lack of obvious signals suggests that the crust of Mars may be more similar to that of the Earth’s moon than that of Earth.
Seismic waves travel farther through solid rock than a heap of loose material like sand. On Earth, the constant churning of plate tectonics generates new solid rocks on the surface. On the moon, there are no more eruptions of lava, and for billions of years the meteor bombardment has shattered the ancient lunar crust into small pieces. The result is a loose top layer, which is why astronauts left so many boot prints on their visits.
“Mars is probably somewhere between the moon and Earth,” Fernando said.
With Perseverance, however, the exact time and location of the landing will be known, and so InSight scientists will know where to look in the seismic data and pull out a tiny signal that would normally be overlooked.
It sounds like how scientists were able to calibrate decades ago the seismometers left on the moon by NASA’s Apollo astronauts when pieces of rockets and moon landers crashed into the moon.
With that knowledge, they could then sift through past data and look for similar patterns that could be meteor impacts.
Fernando and the other InSight scientists also looked at other signals the seismometer could pick up. Perhaps the air pressure waves of the sound boom of the arrival of Perseverance would be enough. Or the sound boom would shake the ground, generating a wave that would travel to InSight.
But their calculations showed that these rumblings would be too small to be detectable.
They also considered looking for bigger parts of the spacecraft, like the heat shield that would also hit the ground. But these will be dropped at lower altitudes and will not travel as fast, generating small seismic waves.
The weather could pose another complication. If winds on Mars are too strong on Thursday, they could disrupt InSight’s seismometer, creating noise that could also obscure the signal of Perseverance’s arrival.
What lies beneath the surface of Mars remains largely a mystery. Indeed, the bowels of the planet have thwarted InSight’s other main objective, to deploy a thermal probe, dubbed the mole, that would sink about 16 feet into Martian soil. But the probe continued to bounce.
The sand around the mole exhibited an unexpected property of agglutination, which prevented sufficient friction for the device to propel more than 14 inches below the surface.
In January, NASA announced it was abandoning the mole. However, the Insight mission has been extended until December 2022, in an effort to collect more seismic data.
From now on, InSight will have to survive the Martian winter. Its solar panels, shrouded in dust, now generate only 27% of energy compared to when they were new and clean. None of the hundreds of dust devils – essentially tiny tornado whirlpools – in the neighborhood came close enough to drive the dust away. Those responsible for the mission are therefore seeking to make the spacecraft operate with less energy, in particular by turning off certain scientific instruments. That should be enough to keep him from freezing to death, which was the fate of NASA’s rover Opportunity in 2018 after it was enveloped in a planet-wide dust storm.
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