NASA's InSight Mars lander acquired on Feb. 18 this image of the area in front of it.
Photo: JPL-Caltech/NASAMars trembles with quakes as it cools, and the Martian crust shrinks like a wizened apple, according to new findings from the National Aeronautics and Space Administration’s InSight lander. These faint tremors are the first ever detected on Mars or any world other than Earth or the Moon, mission scientists said.
Since the InSight’s safe landing on the red planet almost 15 months ago, the spacecraft’s six onboard seismic sensors have detected more than 450 mild marsquakes, the scientists said. The seismic waves, crisscrossing inside the planet’s crust in a variety of frequencies, are giving scientists their first look under the planet’s skin.
“We have finally for the first time established that Mars is a seismically active planet,” said geophysicist Bruce Banerdt at NASA’s Jet Propulsion Laboratory in Pasadena, Calif. He directs an international science team drawn from more than three dozen research facilities. “The seismicity is greater than the Moon but less than the Earth.”
On Monday, the scientists published their initial findings about the Martian interior, atmosphere and magnetic field from the $828 million mission in a series of research papers in Nature Geoscience and Nature Communications.
Quakes may be common on Mars, the scientists said. However, the atmosphere around the shallow impact crater—nicknamed Homestead Hollow—where the InSight probe landed is stirred by thousands of dust-devil swirls that make the area home to the planet’s most turbulent winds.
Inside Mars
Sensors on NASA's Mars InSight lander recorded 450 "marsquakes" in the past year or so giving scientists their first look at the planet's hidden interior.
Estimated depths of Mars’s layers
Wind-blown sand and rocky grit make up a surface crust about 16 feet or so deep. It is so compacted that the probe has been unable to drill more than a few inches deep.
miles
0
Competent basaltic
lava flows
Ancient lava flows make up a layer of heavily fractured bedrock about 5 kilometers thick.
5
Strongly
magnetized
basement rock
10
Rocks with traces of a magnetic field make up a layer from 5 kilometers to about 30 kilometers thick.
15
20
The deep mantle and core of Mars remain a mystery. Scientists hope that stronger marsquakes in the year ahead will generate seismic waves powerful enough to reveal its composition.
Mantle
25
30
Inside Mars
Sensors on NASA's Mars InSight lander recorded 450 "marsquakes" in the past year or so giving scientists their first look at the planet's hidden interior.
Estimated depths of Mars’s layers
Wind-blown sand and rocky grit make up a surface crust about 16 feet or so deep. It is so compacted that the probe has been unable to drill more than a few inches deep.
miles
0
Competent basaltic
lava flows
Ancient lava flows make up a layer of heavily fractured bedrock about 5 kilometers thick.
5
Strongly
magnetized
basement rock
10
Rocks with traces of a magnetic field make up a layer from 5 kilometers to about 30 kilometers thick.
15
20
The deep mantle and core of Mars remain a mystery. Scientists hope that stronger marsquakes in the year ahead will generate seismic waves powerful enough to reveal its composition.
Mantle
25
30
Inside Mars
Sensors on NASA's Mars InSight lander recorded 450 "marsquakes" in the past year or so giving scientists their first look at the planet's hidden interior.
Estimated depths of Mars’s layers
Wind-blown sand and rocky grit make up a surface crust about 16 feet or so deep. It is so compacted that the probe has been unable to drill more than a few inches deep.
miles
0
Competent basaltic
lava flows
Ancient lava flows make up a layer of heavily fractured bedrock about 5 kilometers thick.
5
10
Strongly
magnetized
basement rock
Rocks with traces of a magnetic field make up a layer from 5 kilometers to about 30 kilometers thick.
15
20
The deep mantle and core of Mars remain a mystery. Scientists hope that stronger marsquakes in the year ahead will generate seismic waves powerful enough to reveal its composition.
Mantle
25
30
Estimated depths of Mars’s layers
Wind-blown sand and rocky grit make up a surface crust about 16 feet or so deep. It is so compacted that the probe has been unable to drill more than a few inches deep.
miles
0
Ancient lava flows make up a layer of heavily fractured bedrock about 5 kilometers thick.
Competent basaltic
lava flows
5
10
Rocks with traces of a magnetic field make up a layer from 5 kilometers to about 30 kilometers thick.
Strongly
magnetized
basement rock
15
20
The deep mantle and core of Mars remain a mystery. Scientists hope that stronger marsquakes in the year ahead will generate seismic waves powerful enough to reveal its composition.
Mantle
25
30
Moreover, surprisingly strong traces of the planet’s primordial magnetic field billions of years ago still linger in some rocks around the landing zone, the scientists said. Unlike Mars, Earth today has a protective magnetic field generated by electric currents from the motion of molten iron in the planet’s core, shielding the surface from cosmic rays and charged solar particles.
“We unexpectedly see that there is today a [magnetic] field about 10 times stronger than predicted by satellite observations,” said mission scientist Catherine Johnson, a geophysicist at the University of British Columbia. “That magnetism is essentially frozen in the rocks.”
Mars appears to experience about two tiny quakes a day, although the number has gradually increased over the past year. The scientists don’t know why.
By contrast, geophysicists normally detect about 14,000 sizable quakes on Earth every year. After a powerful earthquake, such as the magnitude 7.1 Ridgecrest earthquake that shook California’s Mojave Desert last July, scientists recorded about 80,000 or so aftershocks within a few weeks of the event.
Of the 174 marsquakes fully analyzed so far, about 150 are high-frequency seismic squeaks that would not rattle a window on Earth, the scientists said.
Related
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- Musk’s Timetable for Mars Spaceship Contrasts With Delays for NASA Capsules (Sept. 30, 2019)
- NASA Calls It Quits for Opportunity Mars Rover (Feb. 13, 2019)
- Scientists Find Evidence of Hidden Lake on Mars (July 25, 2018)
In fact, they appear to be so small that the scientists couldn't determine how far away the epicenters were located or their precise magnitude. None of them would pose a danger to future astronauts or colonists, NASA scientists said.
“We can probably say that Mars is a place where the seismic hazard is extremely low,” said Philippe Lognonné, a geophysicist at the Institut de Physique du Globe de Paris and the lead investigator for the InSight’s seismic experiments.
Marsquakes often originate at much greater depths than on Earth, so their energy usually dissipates before reaching the surface.
Generally, most of the marsquakes likely are caused by the planet gradually cooling and shrinking, the scientists said.
Some of these small tremors might have been caused by the impact of large meteors hitting the ground. Scientists set the lander’s onboard cameras to scan the nighttime Martian sky for telltale streaks of shooting stars but so far haven’t detected any, the scientists said.
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They tracked two of the strongest quakes, measuring about magnitude 4.0, to a region called Cerberus Fossae almost 1,000 miles away, an area of fissures, fault lines and lava flows with signs of ancient volcanic activity.
“That is really intriguing,” said mission deputy principal investigator Suzanne Smrekar at the Jet Propulsion Laboratory. “We wouldn’t expect such recent volcanism in that area.”
For now, however, the deep heart of Mars remains a mystery. No marsquake has generated seismic waves strong enough yet to reveal the composition of the planet’s core. The scientists hope that more powerful quakes in the year ahead will reveal its structure and composition.
“Right now, we have a lot more data than we have conclusions,” said Dr. Banerdt. “It’s still a very mysterious situation.”
Write to Robert Lee Hotz at sciencejournal@wsj.com
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2020-02-24 16:00:00Z
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