The lander cleared enough dust from one solar panel to keep its seismometer
on through the summer, allowing scientists to study the three biggest quakes
they’ve seen on Mars.
On Sept. 18, NASA’s InSight lander celebrated its 1,000th Martian day, or
sol, by measuring one of the biggest, longest-lasting marsquakes the mission
has ever detected. The temblor is estimated to be about a magnitude 4.2 and
shook for nearly an hour-and-a-half.
This is the third major quake InSight has detected in a month: On Aug. 25,
the mission’s seismometer detected two quakes of magnitudes 4.2 and 4.1. For
comparison, a magnitude 4.2 quake has five times the energy of the mission’s
previous record holder, a magnitude 3.7 quake detected in 2019.
The mission studies seismic waves to learn more about Mars' interior. The
waves change as they travel through a planet's crust, mantle, and core,
providing scientists a way to peer deep below the surface. What they learn
can shed light on how all rocky worlds form, including Earth and its Moon.
The quakes might not have been detected at all had the mission not taken
action earlier in the year, as Mars' highly elliptical orbit took it farther
from the Sun. Lower temperatures required the spacecraft to rely more on its
heaters to keep warm; that, plus dust buildup on InSight's solar panels, has
reduced the lander's power levels, requiring the mission to conserve energy
by temporarily turning off certain instruments.
The team managed to keep the seismometer on by taking a counterintuitive
approach: They used InSight's robotic arm to trickle sand near one solar
panel in the hopes that, as wind gusts carried it across the panel, the
granules would sweep off some of the dust. The plan worked, and over several
dust-clearing activities, the team saw power levels remain fairly steady.
Now that Mars is approaching the Sun once again, power is starting to inch
back up.
"If we hadn't acted quickly earlier this year, we might have missed out on
some great science," said InSight's principal investigator, Bruce Banerdt of
NASA's Jet Propulsion Laboratory in Southern California, which leads the
mission. "Even after more than two years, Mars seems to have given us
something new with these two quakes, which have unique characteristics."
Temblor Insights
While the Sept. 18 quake is still being studied, scientists already know
more about the Aug. 25 quakes: The magnitude 4.2 event occurred about 5,280
miles (8,500 kilometers) from InSight—the most distant temblor the lander
has detected so far.
Scientists are working to pinpoint the source and which direction the
seismic waves traveled, but they know the shaking occurred too far to have
originated where InSight has detected almost all of its previous large
quakes: Cerberus Fossae, a region roughly 1,000 miles (1,609 kilometers)
away where lava may have flowed within the last few million years. One
especially intriguing possibility is Valles Marineris, the epically long
canyon system that scars the Martian equator. The approximate center of that
canyon system is 6,027 miles (9,700 kilometers) from InSight.
To the surprise of scientists, the Aug. 25 quakes were two different types,
as well. The magnitude 4.2 quake was dominated by slow, low-frequency
vibrations, while fast, high-frequency vibrations characterized the
magnitude 4.1 quake. The magnitude 4.1 quake was also much closer to the
lander—only about 575 miles (925 kilometers) away.
That's good news for seismologists: Recording different quakes from a range
of distances and with different kinds of seismic waves provides more
information about a planet's inner structure. This summer, the mission's
scientists used previous marsquake data to detail the depth and thickness of
the planet's crust and mantle, plus the size of its molten core.
Despite their differences, the two August quakes do have something in common
other than being big: Both occurred during the day, the windiest—and, to a
seismometer, noisiest—time on Mars. InSight's seismometer usually finds
marsquakes at night, when the planet cools off and winds are low. But the
signals from these quakes were large enough to rise above any noise caused
by wind.
Looking ahead, the mission's team is considering whether to perform more
dust cleanings after Mars solar conjunction, when Earth and Mars are on
opposite sides of the Sun. Because the Sun's radiation can affect radio
signals, interfering with communications, the team will stop issuing
commands to the lander on Sept. 29, though the seismometer will continue to
listen for quakes throughout conjunction.
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