The high-speed barrages last year sent seismic waves
rippling thousands of miles across Mars, the first ever detected near the
surface of another planet, and carved out craters nearly 500 feet (150 meters)
across, scientists reported Thursday in the journal Science.
The larger of the two strikes churned out boulder-size slabs
of ice, which may help researchers look for ways future astronauts can tap into
Mars' natural resources.
The Insight lander measured the seismic shocks, while the
Mars Reconnaissance Orbiter provided stunning pictures of the resulting
craters.
Imaging the craters “would have been huge already,” but
matching it to the seismic ripples was a bonus, said co-author Liliya Posiolova
of Malin Space Science Systems in San Diego. “We were so lucky.”
Mars' atmosphere is thin unlike on Earth, where the thick
atmosphere prevents most space rocks from reaching the ground, instead breaking
and incinerating them.
A separate study last month linked a recent series of
smaller Martian meteoroid impacts with smaller craters closer to InSight, using
data from the same lander and orbiter.
The impact observations come as InSight nears the end of its
mission because of dwindling power, its solar panels blanketed by dust storms.
InSight landed on the equatorial plains of Mars in 2018 and has since recorded
more than 1,300 marsquakes.
“It's going to be heartbreaking when we finally lose communication
with InSight,” said Bruce Banerdt of NASA's Jet Propulsion Laboratory, the
lander's chief scientist who took part in the studies. “But the data it has
sent us will certainly keep us busy for years to come."
The incoming space rocks were between 16 feet and 40 feet (5
meters and 12 meters) in diameter, said Posiolova. The impacts registered about
magnitude 4.
The larger of the two struck last December some 2,200 miles
(3,500 kms) from InSight, creating a crater roughly 70 feet (21 meters) deep.
The orbiter's cameras showed debris hurled up to 25 miles (40 kms) from the
impact, as well as white patches of ice around the crater, the most frozen
water observed at such low latitudes, Posiolova said.
Posiolova spotted the crater earlier this year after taking
extra pictures of the region from orbit. The crater was missing from earlier
photos, and after poring through the archives, she pinpointed the impact to
late December. She remembered a large seismic event recorded by InSight around
that time and with help from that team, matched the fresh hole to what was
undoubtedly a meteoroid strike. The blast wave was clearly visible.
Scientists also learned the lander and orbiter teamed up for
an earlier meteoroid strike, more than double the distance of the December one
and slightly smaller.
“Everybody was just shocked and amazed. Another one? Yep,”
she recalled.
The seismic readings from the two impacts indicate a denser
Martian crust beyond InSight's location.
“We still have a long way to go to understanding the
interior structure and dynamics of Mars, which remain largely enigmatic,” said
Doyeon Kim of ETH Zurich's Institute of Geophysics in Switzerland, who was part
of the research.
Outside scientists said future landers from Europe and China
will carry even more advanced seismometers. Future missions will “paint a
clearer picture” of how Mars evolved, Yingjie Yang and Xiaofei Chen from
China's Southern University of Science and Technology in Shenzhen wrote in an
accompanying editorial.
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