Researchers use InSight for deep Mars measurements
Analysis of NASA lander seismograph data reveals boundaries from crust to
core

Date:
August 5, 2020
Source:
Rice University
Summary:
Using data from NASA's InSight Lander on Mars, seismologists have
made the first direct measurements of three subsurface boundaries
from the crust to the core of the red planet.



FULL STORY ========================================================================== Using data from NASA's InSight Lander on Mars, Rice University
seismologists have made the first direct measurements of three subsurface boundaries from the crust to the core of the red planet.


========================================================================== "Ultimately it may help us understand planetary formation," said Alan
Levander, co-author of a study available online this week in Geophysical Research Letters. While the thickness of Mars' crust and the depth of
its core have been calculated with a number of models, Levander said
the InSight data allowed for the first direct measurements, which can
be used to check models and ultimately to improve them.

"In the absence of plate tectonics on Mars, its early history is mostly preserved compared with Earth," said study co-author Sizhuang Deng,
a Rice graduate student. "The depth estimates of Martian seismic
boundaries can provide indications to better understand its past as
well as the formation and evolution of terrestrial planets in general."
Finding clues about Mars' interior and the processes that formed it are
key goals for InSight, a robotic lander that touched down in November
2018. The probe's dome-shaped seismometer allows scientists to listen to
faint rumblings inside the planet, in much the way that a doctor might
listen to a patient's heartbeat with a stethoscope.

Seismometers measure vibrations from seismic waves. Like circular ripples
that mark the spot where a pebble disturbed the surface of a pond,
seismic waves flow through planets, marking the location and size of disturbances like meteor strikes or earthquakes, which are aptly called marsquakes on the red planet.

InSight's seismometer recorded more than 170 of these from February to September 2019.

Seismic waves are also subtly altered as they pass through different
kinds of rock. Seismologists have studied the patterns in seismographic recordings on Earth for more than a century and can use them to map the location of oil and gas deposits and much deeper strata.

"The traditional way to investigate structures beneath Earth is to
analyze earthquake signals using dense networks of seismic stations,"
said Deng. "Mars is much less tectonically active, which means it
will have far fewer marsquake events compared with Earth. Moreover,
with only one seismic station on Mars, we cannot employ methods that
rely on seismic networks." Levander, Rice's Carey Croneis Professor
of Earth, Environmental and Planetary Sciences, and Deng analyzed
InSight's 2019 seismology data using a technique called ambient noise autocorrelation. "It uses continuous noise data recorded by the single
seismic station on Mars to extract pronounced reflection signals from
seismic boundaries," Deng said.

The first boundary Deng and Levander measured is the divide between Mars'
crust and mantle almost 22 miles (35 kilometers) beneath the lander.

The second is a transition zone within the mantle where magnesium iron silicates undergo a geochemical change. Above the zone, the elements form
a mineral called olivine, and beneath it, heat and pressure compress them
into a new mineral called wadsleyite. Known as the olivine-wadsleyite transition, this zone was found 690-727 miles (1,110-1,170 kilometers)
beneath InSight.

"The temperature at the olivine-wadsleyite transition is an important key
to building thermal models of Mars," Deng said. "From the depth of the transition, we can easily calculate the pressure, and with that, we can
derive the temperature." The third boundary he and Levander measured is
the border between Mars' mantle and its iron-rich core, which they found
about 945-994 miles (1,520-1,600 kilometers) beneath the lander. Better understanding this boundary "can provide information about the planet's development from both a chemical and thermal point of view," Deng said.


========================================================================== Story Source: Materials provided by Rice_University. Note: Content may
be edited for style and length.


========================================================================== Journal Reference:
1. Sizhuang Deng, Alan Levander. Autocorrelation Reflectivity of Mars.

Geophysical Research Letters, 2020 DOI: 10.1029/2020GL089630 ==========================================================================

Link to news story: https://www.sciencedaily.com/releases/2020/08/200805160929.htm

--- up 3 weeks, 1 hour, 55 minutes
* Origin: -=> Castle Rock BBS <=- Now Husky HPT Powered! (1337:3/111)