In May 2018, NASA’s interior exploration with seismic investigations, geodesy and heat transport (InSight) landed on the surface of Mars. This mission is the first of its kind, as all previous orbiters, landers and rovers have focused on studying the surface and atmosphere of Mars. In contrast, InSight was tasked with characterizing the internal structure of Mars and measuring the core, mantle and crust by reading its seismic activity (also known as “Marsquakes”).
The aim is to learn more about the geological development of Mars since its formation 4.5 billion years ago, which should also provide insights into the formation of the earth. According to three recently published articles, the data obtained by InSight has led to new analyzes of the depth and composition of the Martian crust and mantle and confirmed the theory that the planet’s inner core has melted.
The three studies that appeared in the July 23rd issue of Science were directed by Brigitte Knapmeyer-Endrun from the Bensberg observatory at the University of Cologne; Amir Khan, researcher at the Physics Institute of the University of Zurich; and Simon Stähler, researcher at the Institute for Geophysics at ETH Zurich. These publications addressed the new knowledge about the thickness and structure of the Martian crust, the upper mantle structure, and the molten core (each).
Clouds move over the dome-covered seismometer known as SEIS, which is part of NASA’s InSight lander on Mars. Photo credit: NASA / JPL-Caltech
Bruce Banerdt, InSight’s lead researcher at NASA’s Jet Propulsion Laboratory (JPL), said in a recent press release from NASA JPL: We were hoping to be finished. This is the culmination of all the work and worries of the past ten years. “
The data that led to all three publications came from InSight’s seismometer known as the Seismic Experiment for Interior Structure (SEIS). On Mars, seismic activity is largely the result of surface impacts that cause sound waves to travel through the mantle and core to the other side of the planet. The ultra-sensitive SIES was developed so that scientists can hear these sound waves, the speed and shape of which vary depending on the material.
These variations have given seismologists an opportunity to study the internal structure of Mars and learn more about how all rocky planets – including Earth, Venus, and Mercury – work. In all cases, the rocky planets formed from the protoplanetary disk, which consisted of dust and meteoric material left over when the sun was formed. When this material came together, it became a giant ball of molten silicate minerals, metals, and other elements.
Over the course of tens of millions of years, the planet cooled and differentiated into three different layers – the crust, mantle, and core – with the lighter silicate elements settling near the tip and heavier elements (such as iron and nickel) in the core. Measuring the depth, size and structure of these three layers has always been a central part of InSight’s mission and the purpose for which SEIS was developed.
NASA’s InSight lander discovered on July 25, 2019, the 235th seismologists examine the wobble in seismograms to confirm whether they are really seeing a quake or a sound made by the wind. Photo credit: NASA / JPL-Caltech
Since the SEIS was first placed on the Martian surface, it has recorded 733 different Martian quakes, 35 of which (all between magnitudes 3.0 and 4.0) provided the data for all three papers. From this data, Knapmeyer-Endrun and her colleagues determined that the Martian crust is thinner than expected and may have two or three sub-layers. If there are two sub-layers, the crust extends 20 km (12 miles) below the surface or 37 km (23 miles) if there are three.
Meanwhile, Khan and colleagues found that the mantle extends 1560 km (969 miles) below the surface, while Stähler and colleagues found that the core is liquid and has a radius of about 1830 km (1,137 miles). This study is a unique opportunity, ”says Stähler. “It took scientists hundreds of years to measure the Earth’s core; after the Apollo missions it took them 40 years to measure the core of the moon. It took InSight only two years to measure the core of Mars. “
One surprising find was that all of the most significant marsquakes discovered by InSight came from one area: Cerberus Fossae, a region that is volcanically active enough that geophysicists believe that lava may have flowed there in the past eons. This is based, in part, on images captured by orbiting spacecraft that discovered rocky tracks and other landslide features that appear to have been caused by marsquakes.
Another surprise was that none of these quakes came from the more prominent volcanic regions like Tharsis, where the three of the largest volcanoes on Mars are (collectively known as Tharsis Montes). However, there can be many quakes (large and small) that InSight cannot detect due to shadow zones caused by the core breaking seismic waves away from certain areas.
The two largest quakes detected by NASA’s InSight appear to have originated in a region of Mars called Cerberus Fossae. Credits: NASA / JPL-Caltech / Univ. from Arizona.
Meanwhile, InSight’s seismometer detects new marsquakes every day, and the mission team is hoping to detect a marsquake greater than 4.0. “We’d still love to see the big one,” said JPL’s Mark Panning, co-lead author of the paper on the crust. “We have to do a lot of careful processing to get what we want from this data. A bigger event would make everything easier. “
These results are the first of many to come from InSight’s seismic data, which is helping scientists refine their models of Mars and how it was formed. They will also provide valuable information on how Mars lost its magnetosphere about 4.2 billion years ago, followed by the slow depletion of its atmosphere by solar wind over the course of several hundred million years.
This process resulted in Mars moving from a warmer, wetter planet that could have hosted microbial life on its surface, to the icy and arid planet it is today. Knowing how and why this transition occurred will also shed light on how terrestrial planets remain (or do not) inhabitable as they evolve. This knowledge will also help astrobiologists who want to characterize extrasolar planets and limit their potential habitability.
The research was also the subject of a live streaming discussion held on Friday, July 23rd, on NASA TV (which you can watch below), as well as on the NASA app, the agency’s website, and YouTube and Facebook Channels of the JPL appeared. The panel included Mike Panning from NASA Jet Propulsion Laboratory, Amir Khan and Sabine Stanely from John Hopkins University.
Further reading: NASA