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

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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.

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