Twenty-four were relatively strong — magnitude
3 to 4 — and apparently stemmed from distant
underground triggers. The rest were smaller,
with uncertain magnitude and origin. Even the
stronger quakes would not have posed a hazard
to anybody on the planet’s surface, researchers
said in a press conference.
The overall tally has since jumped to more than
450 marsquakes, most of them small, InSight’s
lead scientist, Bruce Banerdt of NASA’s Jet
Propulsion Laboratory, said in an email.
The basic cause of Martian quakes is a long-term
cooling of the planet, which makes it contract,
fracturing its brittle outer layers, Banerdt
told reporters. But it’s not clear what detailed
mechanisms bring on specific quakes, he said.
While the team cannot rule out meteor
impacts, the source of the tremors appears to
be underground, according to the researchers.
Nevertheless, Mars-orbiting spacecraft are on
the lookout for signs of recent impacts, and
InSight’s cameras scan the night sky for meteors.
So far, they’ve come up empty.
Banerdt said he had hoped to find more larger
quakes, which are useful for probing deeper
under the planet’s surface. In an email, he said
“another year of observations will be needed to
complete the goals of the mission.”
InSight landed in a small crater in Mars’
Elysium Planitia in November 2018. Its French
seismometer was placed directly on the volcanic
plain the following month.
This region has especially turbulent weather,
with dust devil-like vortexes.
The lander still has another year of geologic
observations for a total of two years, or one