Every planet has a past. Earth’s geologic history lives in layers, shifting beneath mountain peaks and fallen forests, retreating rivers and rising seas. While we dig for evidence of where we came from, the forces that formed our world billions of years ago continue to churn, burn and make themselves known. With every volcanic blast and earthquake, we understand more about our planet.
In the spirit of discovery, researchers have longed to carry out seismic studies on other planets. However, the opportunity to answer fundamental questions, like, “Are there earthquakes on Mars?”, or marsquakes, was rare — until recently.
Looking Into Mars’ Layers
True to its name, since it arrived on the scene, the Mars InSight lander has been literally looking into what’s going on inside the fourth planet from the sun. InSight is short for Interior Exploration using Seismic Investigations, Geodesy and Heat Transport. It arrived on Mars in a neatly packed, 789-pound (358-kilogram) bundle on November 26, 2018. The landing site near Elysium Mons is known for landslides, evidence of which can be seen from orbit, and two long, shallow trenches around 1,000 kilometers long.
On Earth, such enormous formations are usually caused by geologic activity. Abundant evidence gathered from spacecraft, as well as ground-based telescopes, points to Mars being geologically active in its distant past. Mars is, after all, home to the largest known volcano in the solar system. Soil samples collected by robotic explorers indicate that Martian volcanoes were active as recently as 180 millions years ago — a blink of an eye in geologic time.
The question is: Is Mars still active, with a beating planet heart somewhere beneath the swirling dust and broken, dry lake beds? Are there earthquakes on Mars? Is the core molten or silent and dead?
The answer is yes to all of the above. Geologically speaking, the fourth planet from the sun is very much alive and kicking. Marsquakes rock the surface, subsurface and deep interior of our planetary neighbor. These quakes, while they may appear similar to earthquakes, are motivated by slightly different forces.
Earthquakes vs. Marsquakes
Earthquakes occur as our tectonic plates float on the mantle, colliding and slipping past each other. Quakes on Mars are a result of the entire planet contracting as it cools from its initial formation more than four billion years ago.
It’s also believed that, though there is no spinning dynamo in Mars’ heart to generate a planet-wide magnetic field, magma exists beneath the surface. When the magma moves upward, it creates pressure that pulses through the surface in the form of seismic waves. This form of magmatism can create pressure waves detectable by InSight’s external seismometer, the Seismic Experiment for Interior Structure (SEIS), the first of its kind to reside in the open on the surface of another planet.
What We’ve Learned
The moving and shaking going on beneath Mars’ breathtaking landscape in the last year has taught us much about the planet’s past and present. In July 2021, multiple marsquakes of different sizes allowed planetary scientists to accurately gauge that the core of Mars may still be molten. The scientists running the InSight project have also noticed more quakes happen on the night side of the planet, when cooler temperatures make it easier for the ground to contract. Then, on September 18, a quake larger and longer than any felt before rolled right into SEIS.
SEIS supposedly can hear the tiniest movements, including the shaking of a hydrogen atom. Hearing so exquisitely sensitive has been hardly necessary during this mission. As it turns out, Mars has plenty of high-volume activity, even without the marsquakes. Meteorite strikes, wind, dust devils and landslides all make sounds that SEIS can detect and send back to Earth. Then, as if in celebration of InSight’s 1,000th Sol on Mars, a marsquake not only occurred during the day but also lasted for a full hour and a half.
At magnitude 4.2 on the Richter scale, the September event was one of three marsquakes over 4.0 detected since the beginning of August 2021. This quake was unlike many others InSight has detected since 2018. It didn’t come from Cerberus Fossae, home of the two mysterious rifts in the Martian soil that made it seem likely that Mars was still geologically active. It didn’t come from Elysium Planitia, where InSight is permanently parked. Instead, it came from far away, possibly as far as Valles Marineris, on the other side of the planet. Quakes that pass through an entire planet can provide an unparalleled look into what a world is made of: core, mantle, crust and all the layers in-between.
“Are there earthquakes on Mars?” was answered definitely when InSight detected its first quake on April 6, 2019. Between then and now, all the moving and shaking has allowed humankind to confirm the depth of Mars’ crust, the size of its mantle (969 miles/1,560 kilometers below the surface) and the size of its molten core. Compared to how many decades it took us to measure the Moon’s core (four) and the Earth’s core (dozens), it seems as though humanity’s insight into planetary science has taken a giant, if shaky, leap forward.
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