NASA’s InSight Lander Gives First Look at Mars Interior, Yielding a Big Surprise

Analysis of marsquakes detected by space agency reveals a planet with a large molten region and inner structures markedly different from Earth’s

By Robert Lee Hotz and Merrill Sherman

This artist's concept depicts NASA’s InSight lander after it deployed its instruments on the Martian surface. NASA/JPL-CALTECH

NASA-funded researchers said Thursday they had mapped the interior of Mars, using seismic data collected by the agency’s Mars InSight lander to reveal a planet with a molten core whose size and composition came as major surprises.

The interior map—the first ever created of another planet—shows that the internal structure of Mars differs dramatically from Earth’s. 

Mars has a thicker crust and a thinner underlying mantle layer as well as a core that is bigger, less dense and more liquid than the researchers had expected.

The scientists said their findings, which were described in three papers published Thursday in the journal Science, suggest that Mars formed millions of years before Earth, when the sun was still condensing from a cloud of glowing gas.

“It gives us our first sample of the inside of another rocky planet like Earth, built out of the same materials but very, very different,” Sanne Cottaar, a seismologist at the U.K.’s University of Cambridge, said of the new research. “It is impressive.”

Dr. Cottaar, who wasn’t involved in the new research, called the findings “a major leap forward in planetary seismology.”

The new in-depth portrait of Mars was assembled by an international team of more than 40 scientists working at research centers from Pasadena to Moscow.

The scientists peered into the innards of the red planet using French-built seismometers on board the space agency’s $828 million InSight lander, which in 2018 landed on a smooth plain along the Martian equator called Elysium Planitia.

The instruments captured detailed information about hundreds of marsquakes, including the way the vibrations caused by the alien temblors were reflected and refracted by subsurface layers to reveal their positions and densities.

“The clues don’t lie on the surface,” said Amir Khan, a geophysicist at the University of Zurich in Switzerland and a member of the research team. 

“You have to look inside for the fundamental building blocks that make a planet: the crust, the mantle, the core and the separation of materials that happens as the planet forms.”

The InSight lander has recorded more than 700 marsquakes since beginning operations in February 2019, fewer and less intense than the scientists had expected.

Even the strongest of them, registering at about magnitude 4.0, would barely rattle the windows on Earth. 

The largest quake on Earth in 2020—a magnitude 7.8 temblor that struck Perryville, Alaska—was about 6,000 times more powerful than the biggest marsquake recorded by InSight.

Mars is so seismically stable that InSight’s sensors were able to detect tiny shivers from faults thousands of kilometers away, the scientists said. 

“It is a testament to the quietness of Mars,” said team leader Mark Panning, InSight project scientist at NASA’s Jet Propulsion Laboratory in Southern California. 

“You would never get that quiet on Earth because, no matter where you go, the oceans are always making seismic noise.”

The research showed that the core of Mars has a radius of nearly 1,137 miles (1,830 kilometers) and extends about midway to the planet’s surface. 

As best as the scientists can tell, the molten core isn’t very dense and likely contains a mixture of light elements such as hydrogen, oxygen, carbon and sulfur.

Wrapped around the core is a relatively thin mantle, composed perhaps of just two or three rocky layers. 

These are topped by an unusually thick and rigid outer shell of upper mantle and crust, called the lithosphere, which the scientists said seems to be two or three times thicker than a similar formation on Earth. 

The crust itself was found to have a thickness of between 14 and 44 miles (24 and 72 kilometers).

But Mars might not have given up all its structural secrets. 

The scientists discovered that the rocky soil beneath the lander dissipates seismic energy, meaning that the 794-pound, solar-powered craft may be located within a vast seismic “shadow” where some marsquakes might elude detection.

The new findings from InSight come as NASA’s six-wheeled Perseverance rover prepared to collect its first samples of Martian rock at its landing site, located 2,100 miles from InSight in the Jezero crater. 

Plans call for the $2.7 billion rover to collect up to 43 samples that might contain chemical traces of ancient microbial life—if any ever existed on the now-barren planet—for eventual transport back to Earth.

In this artist’s concept of NASA's InSight lander on Mars, layers of the planet's subsurface can be seen below and dust devils can be seen in the background. / PHOTO: IPGP/NICOLAS SARTER

InSight has been struggling in recent months, as wind-whipped Martian dust collected on its solar panels and cut their ability to generate electrical power. 

In May, NASA engineers directed the probe’s digging tool to pile sand on the lander’s deck so that the wind would blow it across the solar panels and, like a whisk broom, sweep away the dust.

“We dump sand on ourselves to get rid of dust,” Dr. Panning said, adding that the fix seemed to be working.

The lander recently was granted a two-year extension for scientific work, now lasting until the end of 2022.

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