An impression of an artist of the inner structure of Mars. The uppermost layer is the crust, and beneath it is the mantle, which rests on a solid inner core. Credit: Image with ease from NASA / JPL-Caltech)
Use of data from NASAInSight Lander on March, Seismologists from Rice University have made the first direct measurements from three boundaries below the base of the crust to the core of the red planet.
This February 2, 2019 photo shows the robotic arm on NASA’s InSight Lander deploying an umbrella cover that protects the lander’s seismometer from wind, dust and extreme temperatures. Credit: Image courtesy of NASA / JPL-Caltech
“Ultimately, it may help us understand planetary formation,” said Alan Levander, co-author of a study published this week in Geophysical research letters. While the thickness of Mars’ crust and the depth of its core have been calculated using a number of models, Levander said the InSight data allowed for the first direct measurements, which can be used to check models and eventually improve them. .
“In the absence of flat tectonics on Mars, its early history is mostly preserved compared to Earth,” said co-author Sizhuang Deng, a student of Rice. “Martia’s depth estimates of Martian boundaries can provide clues to better understand the past, such as the formation and evolution of Earth planets in general.”
Finding guidelines about the interior of Mars and the processes that shaped it are key goals for InSight, a robot lander that will launch in November 2018. The dome-shaped seismometer of the probe enables scientists to listen for foul jumble on the planet, in many ways that a doctor might be listening to the heartbeat of a patient with a stethoscope.
Seismometers measure vibrations of seismic waves. Like circular ripples that mark the place where a pebble disrupts the surface of a pond, seismic waves flow through planets, marking the location and magnitude of disturbances such as meteor showers or earthquakes, which are indicated on the red planet . The InSight seismometer recorded more than 170 of these from February to September 2019.
A mosaic of Mars composed of 102 Viking Orbiter images. Credit: Image courtesy of NASA / JPL-Caltech
Seismic waves are also subtly altered as they pass through different types of rock. Seismologists have studied the patterns in seismographic surveys on Earth for over a century and can use them to map the location of oil and gas deposits and much deeper layers.
“The traditional way to study structures beneath Earth is to analyze earthquake signals with dense networks of seismic stations,” Deng said. “Mars is much less tectonically active, which means it will have far fewer marsquake events compared to Earth. Moreover, with only one seismic station on Mars, we can not use methods that rely on seismic networks. ”
Levander, Rice’s Carey Croneis professor of Earth, Environmental and Planetary Sciences, and Deng analyzed InSight’s seismology data from 2019 using a technique called ambient noise autocorrelation. “It continuously uses noise data recorded by the single seismic station on Mars to extract pronounced reflection signals from seismic boundaries,” Deng said.
The first boundary that Deng and Levander measure is the separation between the crust and mantle of Mars nearly 35 kilometers below the lander.
The second is a transition zone within the mantle, in which magnesium iron silicates undergo a geochemical change. Above the zone the elements form a mineral called olivine, and below the compression they heat up and press into a new mineral called wadsleyite. Known as the transition of olivine wadsleyite, this zone was found 690-727 miles (1,110-1,170 kilometers) under InSight.
“The temperature at the oil-wadsleyite transition is an important key to building Mars thermal models,” Deng said. “From the depth of the transition we can easily calculate the pressure, and with that we can lower the temperature.”
The third boundary he and Levander measure is the boundary between the mantle of Mars and its iron-rich core, which they found about 920-994 miles (1,520-1,600 kilometers) below the lander. A better understanding of this boundary “can provide information about the evolution of the planet from both a chemical and thermal point of view,” Deng said.
Reference: “Autocorrelation Reflectivity of Mars” by Sizhuang Deng and Alan Levander, August 4, 2020, Geophysical research letters.
DOI: 10.1029 / 2020GL089630
The research was supported by Rice’s Department of Earth, Environmental and Planetary Sciences.
