Before the NASA InSight lander plunged through Mars’ atmosphere and parachuted its way down to the planet’s surface, scientists were already pretty familiar with the surface of Mars, but not what was on the inside.

“We’ve got 15 years of information about the surface, we’ve measured the topography, the atmosphere, the magnetic field — but we really haven’t had any understanding of what it’s made out of,” Bruce Banerdt, principal investigator of InSight Mission, tells Inverse. “Understanding the basic building blocks of the planet has been pretty much guesswork up until now.”

InSight was packed with a host of instruments to look deep into Mars. A new discovery found deep layers of lava flows dating back billions of years. Mars’ ancient volcanic activity can help scientists put together the events of its potentially habitable past and understand Earth’s evolutionary past as well.

A team of planetary scientists including Barendt published their findings in a paper released Monday in the journal Nature Communications.

HERE’S THE BACKGROUND — Mars has some of the largest volcanoes amongst all the other planets of the Solar System. Although the planet’s volcanoes are not active today, their past activity has left tracks that mark the surface of Mars.

The Mars Odyssey mission captured an overview of the long volcanic fields in Mars’ Tharsis region.NASA/JPL-Caltech/ASU

Previous missions to Mars captured images of the surface showing lava flows extending for hundreds of miles. NASA’s Viking Lander, the first spacecraft to land on Mars in 1976, captured images of lava flows from the Martian volcano Elysium, which extended across plains near Mars’ equator.

More than 40 years later, InSight landed at the Elysium Planitia region of Mars to probe into its internal structure and explore beneath its surface. NASA’s InSight mission is the first to measure the subsurface of Mars using seismic methods, studying elastic waves inside the planet itself to detail its subsurface.

WHAT’S NEW — The scientists behind the recent discovery analyzed seismic data that had been collected by the InSight mission to uncover the composition of Elysium Planitia.

They picked up signals from about 200 meters beneath the planet’s surface and found different layers of ancient lava flows and sedimentary rock.

The Elysium Planitia region has a top layer of sandy material that extends about three meters beneath the surface, followed by a 15-meter layer of a coarse rocky layer that was likely ejected following a meteorite impact before falling back onto the surface.

Beneath the top layer is around 150 meters of dried lava flows dating back to about 1.7 billion years ago, during Mars’ Amazonian period. Scientists believe this period to have begun about 3 billion years ago when Mars experienced similar conditions to the way it is today, with a lower rate of asteroid and meteorite impacts and lower temperatures.

The scientists also identified an older layer of lava flows dating back to about 3.6 billion years during the Hesperian period, which experienced a high rate of volcanic activity.

These two layers of lava flows had a layer of sedimentary rock wedged in between, which was about 30 to 40 meters thick.

“The nice thing about this investigation is it gives a really clear indication of a lava flow over a sedimentary layer which overlays another lava flow,” Banerdt, a co-author on the paper, says.

Although other evidence has shown lava flow structures across Mars, this discovery provides a clear timeline of volcanic activity on Mars based on the different layers that have formed beneath the planet’s surface.

“This helps to tie this to trying to figure out what the timing was between the various different activities,” Banerdt says. “The fact that you’ve got this sedimentary layer that is sandwiched between these two volcanic stones tells that there was a pause in the volcanic activity, a fairly long pause because it takes a long time for the sedimentary rocks to form.”

“This is giving the geologists information about the fact that we’ve got not just sort of a uniform history of volcanism, but that maybe it happens in several different pulses,” he adds.

WHAT’S NEXT — Over the past decades, several missions to Mars have captured little pieces of information that put together the larger picture of the planet’s history.

This information not only helps scientists better understand Mars’ potential past habitability and whether or not the planet ever harbored life, but it also helps them get a better idea of how Earth evolved over time.

Out of the planets in the Solar System, Mars is the most similar to Earth in composition. By investigating the planet’s evolution over time, scientists are also trying to figure out how Earth became the rocky body it is today.

“We have a pretty good idea of the structure of the Earth, but we don’t understand really well how it got to be that way,” Banerdt says.

On Mars, a lot of the data of the early processes that shaped the planet are still fairly intact since the planet did not undergo a lot of the same geological activity as Earth.

“It’s a lot more pristine on Mars,” Banerdt says. “And so we can look at Mars’ internal structure, and infer to a large extent that that’s what the Earth might have looked like 4.5 billion years ago and basically be able to understand better how the Earth formed.”

Abstract: Orbital and surface observations can shed light on the internal structure of Mars. NASA’s InSight mission allows mapping the shallow subsurface of Elysium Planitia using seismic data. In this work, we apply a classical seismological technique of inverting Rayleigh wave ellipticity curves extracted from ambient seismic vibrations to resolve, for the first time on Mars, the shallow subsurface to around 200 m depth. While our seismic velocity model is largely consistent with the expected layered subsurface consisting of a thin regolith layer above stacks of lava flows, we find a seismic low-velocity zone at about 30 to 75 m depth that we interpret as a sedimentary layer sandwiched somewhere within the underlying Hesperian and Amazonian aged basalt layers. A prominent amplitude peak observed in the seismic data at 2.4 Hz is interpreted as an Airy phase related to surface wave energy trapped in this local low-velocity channel.



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