The successful Mars InSight mission employed a NASA/European Space Agency robotic lander designed to study the interior of Mars. The mission recently ended with last contact on Dec. 15, 2022 as its dust choked solar panels failed to deliver enough electricity to keep InSight going.
The “Interior Exploration using Seismic Investigations, Geodesy and Heat Transport” lander was managed by NASA’s Jet Propulsion Laboratory and manufactured by Lockheed Martin Space, and most of its scientific instruments were provided by European agencies. The mission was launched on May 5, 2018. InSight landed in Elysium Planitia on Mars on Nov. 26, 2018.
InSight had two science goals:
- Seek to determine the interior structure and composition of Mars and to reveal how a rocky planet forms
- Study the rate of Martian tectonic activity and meteorite impacts
Seismic Results
InSight deployed a successful, very sensitive seismometer on Mars’ surface for the first time. The seismometer was covered with a windshield to avoid false signals from windstorms.
InSight’s seismometer recorded more than 1,300 seismic events. Most of these were Mars quakes, but the seismometer also recorded meteor impacts. One registered magnitude 4. The impact crater that formed Dec. 24, 2021, by a meteoroid strike in the Amazonis Planitia region of Mars, is about 150 meters across. It was discovered by the orbiting Mars Reconnaissance Orbiter. More than 50 events provided strong, clear signals to enable the team to derive quake or meteor impact location on Mars. This region has evidence of recent volcanism within the last 2 million years. The six largest events were recorded since mid-2021. The strongest was in May 2022. It was estimated to be magnitude 5, with reverberations through Mars for six hours.
InSight had a second geophysical instrument package designed to measure Mars’ heat flow. The instrument was named Heat Flow and Physical Properties Package (HP3), also known as “the mole.” The mole is a 40-centimeter-long pile driver with embedded temperature sensors connected to the lander by a tether. The sensors were to measure heat flowing from Mars’ interior once the mole dug at least 3 meters deep. The mole was unable to gain the friction it needed to dig into Mars’ soil regolith. The team stopped attempts to drive in the mole in January 2021.
Mars, like Earth, heated up and melted as the gas, dust and meteoritic material accreted by gravity in the early solar system. Over time, Mars differentiated into distinct layers of crust, mantle and core. InSight’s goal was to define the depth, thickness and density of these layers. We use the Earth as a laboratory to understand the geology of Mars’ crust and mantle. Geologists study surface geology and drill cores to learn about Earth’s crust. We know about the composition of Earth’s mantle from rare geologic processes that bring mantle material to the surface.
Obduction is a tectonic process that thrusts oceanic crust and even upper mantle onto continental crust at a convergent plate boundary. This allows us to sample upper mantle material such as peridotite, a dense, coarse-grained igneous rock consisting mainly of olivine and pyroxene. It is rich in magnesium and iron. Kimberlite pipes on Earth allow us to sample material from the lower mantle. Kimberlite is an igneous rock variant of peridotite.
We understand the composition of Earth’s core by knowing its density from seismology and by analogy to meteorites derived from early solar system planetesimals that were differentiated into crust, mantle and core. Many planetesimals were completely disrupted by cataclysmic collisions early in the history of the solar system. Their debris falling as meteorites tell the story. Iron meteorites are primarily composed of nickel and iron derived from the disrupted core of such a planetesimal.
S waves cannot pass through liquids, and do not pass through Earth’s core because the outer core is molten liquid. Seismic P waves pass through all layers of the Earth, while S waves cannot pass through the liquid core, resulting in an S-wave shadow on the opposite side of the quake event.
The earthquakes most people feel come from faults, or rock fractures, slipping along tectonic plate boundaries. Mars has no tectonic plate boundaries, so its crust is like one giant plate. However, faults do form in the Martian crust due to compressional stresses from the slight shrinking of Mars as it continues to cool.
The initial seismogram wiggles are P waves followed by S waves. These waves can return after reflecting off layers inside the planet. This facilitates analysis of the internal layers and detail sub-layers within the crust.
The core at the center of Mars has a radius of 1,830 kilometers. By analogy to Earth and P-wave velocity measurements, the core is composed of iron, nickel and sulfur. The Martian core is richer in sulfur than Earth’s. Determining that the core is molten and measuring its size was an exciting result.
Seismologist Simon Stähler of ETH Zurich said, “This study is a once-in-a-lifetime chance. 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.”
Surrounding the Martian core is a rocky mantle between 1,240 and 1,880-kilometers thick. The Martian mantle, like Earth, is rich in iron and magnesium but richer in potassium and phosphorus than Earth’s. The crust of Mars is between 10 and 50-kilometers thick. The crust is made of iron, magnesium, aluminum, calcium and potassium. Igneous basalt is common.
Volcanism on Mars
Scientists from the University of Arizona have given more perspective on Martian geodynamics with a report on the discovery of an active mantle plume raising the surface and generating earthquakes and recent volcanic eruptions.
“Our study presents multiple lines of evidence that reveal the presence of a giant active mantle plume on present-day Mars,” said Adrien Broquet of the Lunar and Planetary Laboratory at University of Arizona.
Elysium Planitia, where the InSight probe landed, has the youngest volcanic eruption known on Mars. There was a small explosion of volcanic ash about 53,000 years ago. Volcanism there originates from young fissures known as Cerberus Fossae. They extend more than 1,300 kilometers across the Martian surface. NASA’s InSight team found that nearly all Mars quakes originate in this area. When researchers applied tectonic modeling to the area, they determined that a giant mantle plume, 4,000-kilometers wide, was the only way to explain the extension in Cerberus Fossae.
“We used to think that InSight landed in one of the most geologically boring regions on Mars – a nice flat surface that should be roughly representative of the planet’s lowlands,” said Broquet. “Instead, our study demonstrates that InSight landed right on top of an active plume head.”
‘Sad but Celebratory’
While InSight returned invaluable seismogram data and could have kept going recording Mars quakes, it succumbed to the thickening dust on its solar panels, drastically reducing energy to charge its batteries. The last communication with InSight was in December last year. InSight sent a very sad Tweet, “My power’s really low, so this may be the last image I can send. Don’t worry about me though: my time here has been both productive and serene. If I can keep talking to my mission team, I will – but I’ll be signing off here soon. Thanks for staying with me.”
NASA then concluded the InSight Mission. Associate administrator of NASA’s Science Mission Directorate, Thomas Zurbuchen, said, “I watched the launch and landing of this mission, and while saying goodbye to a spacecraft is always sad, the fascinating science InSight conducted is cause for celebration. The seismic data alone from this Discovery Program mission offers tremendous insights not just into Mars but other rocky bodies, including Earth.”
