For the first time in history, the landing of a spacecraft on Mars might be 鈥渉eard鈥� in an unusual way 鈥� by the seismic waves it produces as it punches the surface of the planet.
The ears in this scenario are built into NASA鈥檚 InSight lander, which touched down in a region called Elysium Planitia on Mars in 2018. Since then, the stationary lander has been using instruments to study the planet鈥檚 geology, including a seismometer to detect seismic waves, and has found hundreds of seismic events known as marsquakes.
The lander will soon be joined on Mars by NASA鈥檚 Perseverance rover, which is scheduled to touch down on 18 February 2021. Benjamin Fernando at the University of Oxford and his colleagues have found that InSight might be able to detect the seismic waves from the landing, a first in planetary exploration.
Advertisement
鈥淚t鈥檚 never been done before because there hasn鈥檛 been a seismometer on the surface of another planet before,鈥� he says, although seismometers deployed on the moon by some of the Apollo missions did catch the impacts of rocket boosters from later missions that struck the surface. Fernando and his team鈥檚 research was presented at a meeting of the American Geophysical Union on 10 December.
Perseverance鈥檚 entry capsule will hit Mars鈥檚 atmosphere at about 19,000 kilometres per hour, then take around 7 minutes to reach the surface. This will create an enormous sonic boom that InSight could detect,聽says Fernando,聽but he stresses that the lander鈥檚 seismometer is unlikely to be sensitive enough to do so.
What is more plausible is that seismic waves may be detected when Perseverance drops two stabilising dummy weights called the cruise mass balance devices聽during the landing process, which are blocks of tungsten weighing 77 kilograms each. These will strike the surface with a force comparable to a small car making impact at thousands of kilometres per hour, sending so-called body waves through the interior of Mars, says Fernando.
Despite InSight being located about 3500 kilometres away from Perseverance鈥檚 landing site at Jezero crater, these impacts could be seismically loud enough for InSight to hear them as long as there isn鈥檛 too much background noise from the local Martian weather.
If conditions are just right, both a non-detection or detection would be useful. The former would provide a limit for the seismometer鈥檚 sensitivity, while the latter would give the precise date, time and magnitude of an impact of known size. This could help identify meteorite impacts in InSight鈥檚 seismic data, which were expected but haven鈥檛 been found yet 鈥� even when a small聽new crater formed near the lander in 2019.
鈥淲e can look at some of our previous detections and see if they have some of the same characteristics,鈥� says Bruce Banerdt at NASA鈥檚 Jet Propulsion Laboratory in California, the InSight mission鈥檚 lead.
The landing of China鈥檚 Tianwen-1 rover, which is expected by April 2021, could also be heard by InSight, but more information about how and when it will touch down is needed. 鈥淚f anyone who does have the right information about Tianwen-1 is happy to collaborate, that would be really great,鈥� says Fernando.
Sign up to our free Launchpad newsletter for a voyage across the galaxy and beyond, every Friday
