Mars has a moderate level of seismic activity, halfway between Earth and the Moon, say scientists

All the marsquakes have been detected during quiet periods at night, show preliminary results from NASA’s InSight mission

                            Mars has a moderate level of seismic activity, halfway between Earth and the Moon, say scientists
This artist's concept depicts NASA's InSight lander after it has deployed its instruments on the Martian surface. (NASA/JPL-Caltech)

The Red Planet has a moderate level of seismic activity, intermediate between Earth and the Moon, according to what researchers describe as the first direct measurements of seismic activity and ground vibrations on Mars. 

All of the marsquakes have been detected during quiet periods at night, but the geologic activity likely persists throughout the day, say scientists.

A team of experts, which includes geologists from the University of Maryland (UMD), have released these preliminary results from the InSight mission, which landed a probe on Mars on November 26, 2018. The Mission is scheduled to continue collecting data through 2020.

According to the research team, what is so spectacular about this data is that it gives scientists a “beautifully picture” of what a day is actually like on another planet.

“Data from the mission's Seismic Experiment for Interior Structure (SEIS) have provided the first direct seismic measurements of the Martian subsurface and upper crust, which is the rocky outermost layer of the planet,” says the paper, which has been published in Nature Geoscience.

Before this, NASA’s InSight lander detected the first known “marsquake” on April 6, 2019, 128 days after landing on the planet in November 2018. The quake was the first to be detected on a planetary body other than Earth or Moon.

The InSight lander deployed its seismometer on the Martian surface on December 19, 2018. This image, captured on February 2, 2019 (Martian Sol 66) by the deployment camera on the lander's robotic arm shows the protective wind and thermal shield which covers the seismometer. (NASA/JPL-Caltech)

Seismic data for the current study -- collected over 235 Martian days -- showed 174 seismic events or marsquakes. Of those, 150 were high-frequency events that produce ground-shaking similar to that recorded on the Moon by the Apollo program. According to the analysis, their waveforms show that seismic waves “bounce around” as they travel through the “heterogeneous and fractured Martian crust.” 

Another 24 quakes observed by SEIS were predominantly low-frequency events. Three showed two distinct wave patterns similar to quakes on Earth caused by the movement of tectonic plates.

Based on how the different waves “propagate through the crust,” scientists can identify geologic layers within the planet and determine the distance and location to the source of the quakes. In the current study, the researchers identified the source location and magnitude of three of the low-frequency marsquakes, and believe that 10 more are strong enough to reveal their source and magnitude once they are analyzed.

“This is the first mission focused on taking direct geophysical measurements of any planet besides Earth, and it's given us our first real understanding of Mars' interior structure and geological processes. The data is helping us understand how the planet works, its rate of seismicity, how active it is and where it's active,” says co-author of the study, Nicholas Schmerr, who is an assistant professor of geology at UMD, in the paper.

Understanding the geological processes on Mars can help answer other questions, such as whether the planet can support life, or whether it ever did.

“Detecting signs of life was the primary mission of the earlier Mars probes, Viking 1 and Viking 2. Each carried seismometers, but they were mounted directly on the landers and provided no useful data. The Viking 1 instrument did not unlock properly, and Viking 2 only picked up noise from wind buffeting the lander but no convincing marsquake signals,” says the research team.

This is the first image taken by NASA’s InSight lander on the surface of Mars. (NASA/JPL-Caltech)

The InSight mission is dedicated specifically to geophysical exploration. A robotic arm on the lander placed the SEIS seismometer directly on the Martian ground some distance away to isolate it from the lander.

The instrument is also housed in a vacuum chamber and covered by a Wind and Thermal Shield. The SEIS seismometer is sensitive enough to detect very faint ground vibrations -- they are 500 times quieter on Mars than ground vibrations found in quietest locations on Earth.

The seismometer also provided important information about Martian weather. The researchers found that the winds pick up from about midnight through early morning, as cooler air rolls down from highlands in the Southern Hemisphere onto the Elysium Planitia plains in the Northern Hemisphere, where the lander is located.

“During the day, heating from the sun causes convective winds to build. Winds reach their peak in the late afternoon when atmospheric pressure drops and dust devil activity occurs. By evening, the winds die down, and conditions around the lander become quiet. From late evening until about midnight, atmospheric conditions are so quiet, the seismometer can detect the rumblings from deeper inside the planet,” says the study.

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