Tuesday, April 30, 2019

What's a Marsquake?

On April 23rd, NASA InSight scientists announced they had detected a small seismic event on Mars, aptly referred to as a marsquake. This event, the first of its kind ever detected, promises to bring revolutionary insights about planetary interiors and seismic activity on other worlds.

"InSight's first readings carry on the science that began with NASA's Apollo missions," said InSight Principal Investigator Bruce Banerdt at the Jet Propulsion Laboratory in Pasadena, California. "We've been collecting background noise up until now, but this first event officially kicks off a new field: Martian seismology."

A recording of the quake, which occurred on Martian sol 128 (known to earthlings as April 6th), emits a faint, almost eerie noise. The quake itself would have been so weak that, had it occurred on earth humans wouldn’t even feel it. To even hear it, the video below was sped up by a factor of 60.

Video of seismic event detected by Mars InSight Rover  Credits: NASA/JPL-Caltech/CNES/IPGP/Imperial College London

The NASA InSight (Interior Exploration using Seismic Investigations, Geodesy and Heat Transport) mission seeks to probe the “inner space” of mars. Using the instruments deployed on its lander, scientists hope to learn about the Martian interior, and on a deeper level, understand how it formed billions of years ago. To this goal, InSight equipped their spacecraft with a French Space Agency seismometer (SEIS), an instrument that measures subtle vibrations in the ground. Over 45 missions have explored the surface of Mars, but InSight is the first to successfully deploy a seismometer.

To send anything into space, it needs to be durable. After surviving a 6-month journey through space to reach the red planet, the SEIS is being exposed to weather beyond anything on earth. From temperatures that can dip down to -225 degrees Celcius, to massive dust storms that can cover the entire planet, Mars is not an ideal spot for a robot vacation.

Animation of InSight deploying the SEIS. Credit: NASA/JPL-Caltech 

Issues such as these are why it took scientists over 40 years and 15 proposals to successfully place a seismometer on Mars. When NASA’s first landers departed for the red planet in the late 1970s, seismometers were added to the Viking Landers, but unfortunately, the mechanical unlocking system failed, and the instruments could not be deployed.

We’ve been waiting months for a signal like this,” said Philippe Lognonné, SEIS team lead at the Institut de Physique du Globe de Paris (IPGP) in France. “It's so exciting to finally have proof that Mars is still seismically active. We're looking forward to sharing detailed results once we've had a chance to analyze them.”

Scientists are so interested in studying seismicity on Mars because their triggering mechanism is so different than earth’s. On earth, Earthquakes are caused by the motion and jostling together of segments of the surface called tectonic plates. These are always either drifting apart from, sliding past, or sinking beneath one another. These rigid plates move with the subtlety and grace of a car traveling on a muddy dirt road; initially moving, then getting stuck, then jolting violently forward. When a rocky plate gets “stuck” while moving past another, an incredibly high amount of stress builds. The sudden release of that stress is what causes most earthquakes. 

Earthquakes are more common than you think; there’s likely a small earthquake happening on our planet right now. On Mars though, earthquakes are very rare, and very small, and have little effect on the daily life of our beloved Mars rovers. While I would certainly watch a disaster movie with Dwayne “The Rock” Johnson on Mars saving all the science robots, they’re not in any danger from cataclysmic marsquakes.

An artist’s rendering of a potential action thriller about marsquakes. Stay tuned for the sequel, 2 Mars 2 Furious, and the third in the trilogy, Marsquake: Tokyo Drift.

This is because, unlike earth, Mars doesn’t have tectonic plates. Researchers aren’t certain what causes martian seismicity, which is why the installation of the SEIS is so exciting. Quakes on Mars could be from meteor impacts, from magma disturbing the crust as it rises to the surface, or even from the planet slowly cooling and contracting over time.

NASA is so interested in these marsquakes not only for their effects at the surface, but for their insights about what lies beneath. Learning about the interior will help scientists learn how Mars formed; why it's so similar, yet so alien compared our home.

 The key to their geophysical studies is the relationship between seismic energy and the materials it passes through. When a quake occurs, both compressional (P-waves) and transverse (S-waves) waves radiate from the epicenter. These waves travel at different speeds depending on the material they interact with, and notably, S-waves cannot travel through liquids. By looking at how these waves travel through Mars, scientists may learn about the composition, heat flux, and phase dynamics inside of Mars.

 One of the many questions on researcher’s minds is how Mars lost its magnetic field. On earth, our magnetic field blocks harmful solar radiation, allowing plants and animals to survive on its surface. Scientists hypothesize that a compositional change in the Martian core destroyed its magnetic field billions of years ago, which is one of the reasons why Mars is uninhabitable. Future studies of these quakes will answer all sorts of questions about our planetary neighbor.

 “We are delighted about this first achievement,” said Charles Yana, SEIS mission operations manager at CNES, “and are eager to make many similar measurements with SEIS in the years to come.”

 –Lissie Connors

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