According to the first reports, Mars has been found to have a moderate level of seismic activity and ground vibrations, intermediate between Earth and the Moon. The findings are based on preliminary results from the InSight mission, which landed a probe on Mars on November 26, 2018. This mission is scheduled to continue collecting data through 2020.
The first direct seismic measurements of the Martian subsurface and upper crust-the rocky outermost layer of the planet were provided by an international team which includes the University of Maryland geologists that released data from the mission's Seismic Experiment for Interior Structure (SEIS). The results were published in a special issue of the journal Nature Geoscience on Monday, February 24.
Nicholas Schmerr, an assistant professor of geology at UMD and a co-author of the study said, "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". "These data are helping us understand how the planet works, its rate of seismicity, how active it is and where it's active", he added.
The seismic data was acquired from 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. Their waveforms show that seismic waves bounce around as they travel through the heterogeneous and fractured Martian crust. The other 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.
"These low-frequency events were really exciting because we know how to analyze them and extract information about the subsurface structure," said Vedran Lekic, an associate professor of geology at UMD and a co-author of the study. "Based on how the different waves propagate through the crust, we can identify geologic layers within the planet and determine the distance and location to the source of the quakes."
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 analysed.
"Understanding these processes is part of a bigger question about the planet itself," Schmerr said. "Can it support life, or did it ever? Life exists at the edge, where the equilibrium is off. Think of areas on Earth such as the thermal vents at the deep ocean ridges where chemistry provides the energy for life rather than the Sun. If it turns out there is liquid magma on Mars, and if we can pinpoint where the planet is most geologically active, it might guide future missions searching for the potential for life."
The initial two Mars probes; Viking 1 and Viking 2 were designed for detecting signs of life. 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.
However the InSight mission is dedicated specifically to geophysical exploration, so engineers worked to solve previous noise problems. 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 the aptly named Wind and Thermal Shield. The SEIS seismometer is sensitive enough to discern very faint ground vibrations, which on Mars are 500 times quieter than ground vibrations found in quietest locations on Earth. In addition, the seismometer provided important information about Martian weather.
Low-pressure systems and swirling columns of wind and dust called dust devils lift the ground enough for the seismometer to register a tilt in the substrate. High winds flowing across the surface of the ground also create a distinct seismic signature. Combined with data from meteorological instruments, SEIS data help paint a picture of the daily cycles of surface activity near the InSight lander.
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 is able to detect the rumblings from deeper inside the planet. All of the marsquakes have been detected during these quiet periods at night, but the geologic activity likely persists throughout the day.
"What is so spectacular about this data is that it gives us this beautifully poetic picture of what a day is actually like on another planet," Lekic said.
(With inputs from ANI)