Insight into the inside of Mars

While NASA’s Perseverance rover has captured headlines with stunning pictures of the Martian landscape this year, an older, less-celebrated Mars mission just delivered a big discovery.

For more than two years, NASA’s InSight robotic lander has stayed in one place on Mars’ surface listening for seismic waves and probing the planet’s depths. Now, in a trio of papers in Science, researchers working with NASA’s Jet Propulsion Laboratory and data from InSight revealed the first model of Mars’ interior structure.

“This study is a once-in-a-lifetime chance,” said Swiss researcher Simon Stähler, who served as lead author for one of the papers. “It took scientists hundreds of years to measure Earth’s core; after the Apollo missions, it took them 40 years to measure the moon’s core. InSight took just two years to measure Mars’ core.”

InSight is one of four ongoing missions on the red planet. Along with the derelict hulks of previous American and Soviet missions, Mars currently hosts a Chinese rover that landed in May, the Perseverance rover with the Ingenuity helicopter that landed earlier this year, and the Curiosity rover that touched down in 2012. While the rovers are designed to study Martian topography and study the planet’s surface, NASA engineers designed InSight for a different mission.

The nearly 800-pound InSight lander arrived in November 2018 and within months began conducting experiments. InSight uses a seismometer to track seismic activity—marsquakes—and help researchers create the first accurate model of Mars’ interior structure.

Just like Earth, Mars has a crust that forms the surface of the planet, a mantle below that, and a core. But that may be where the similarities end. Earth’s crust is separated into tectonic plates that slide or rub against one another to create earthquakes. According to the researchers, Mars’ lacks a system of plate tectonics. But the red planet still produces seismic activity because of fissures that have developed in the planet’s crust as it cools and shrinks. Since touching down in 2018, InSight’s ultrasensitive seismometer has detected 733 separate marsquakes, including about three dozen that would reach 3.0 to 4.0 magnitude if measured on Earth.

Studying how waves produced by the marsquakes bounce around the planetary interior led to arguably one of the project’s most surprising discoveries. The InSight team says Mars’ core is much larger than expected: Its radius is 1,137 miles—about half the radius of the entire planet. Despite being so big relative to the planet, the core is also significantly less dense than previously assumed, the researchers say.

“The core is quite large—on the high end of what we expected before the mission. And the density is on the low end of what we expected. And the reason that’s interesting is because there are big implications for how Mars created its magnetic field long ago,” said InSight researcher and Johns Hopkins planetary physicist Sabine Stanley. “That has important implications for Mars’s atmosphere. And as soon as you start mentioning atmospheres, you start connecting to whether or not Mars was habitable in its early life.”