Anatomy of the red planet: Mars-quakes reveal interior

Date:
July 22, 2021
Source:
ETH Zurich
Summary:
Researchers have been able to use seismic data to look inside Mars
for the first time. They measured the crust, mantle and core and
narrowed down their composition.



FULL STORY ========================================================================== Since early 2019, researchers have been recording and analysing marsquakes
as part of the InSight mission. This relies on a seismometer whose data acquisition and control electronics were developed at ETH Zurich. Using
this data, the researchers have now measured the red planet's crust,
mantle and core -- data that will help determine the formation and
evolution of Mars and, by extension, the entire solar system.


==========================================================================
Mars once completely molten We know that Earth is made up of shells:
a thin crust of light, solid rock surrounds a thick mantle of heavy,
viscous rock, which in turn envelopes a core consisting mainly of iron
and nickel. Terrestrial planets, including Mars, have been assumed to
have a similar structure. "Now seismic data has confirmed that Mars
presumably was once completely molten before dividing into the crust,
mantle and core we see today, but that these are different from Earth's,"
says Amir Khan, a scientist at the Institute of Geophysics at ETH Zurich
and at the Physics Institute at the University of Zurich. Together with
his ETH colleague Simon Sta"hler, he analysed data from NASA's InSight
mission, in which ETH Zurich is participating under the leadership of
Professor Domenico Giardini.

No plate tectonics on Mars The researchers have discovered that the
Martian crust under the probe's landing site near the Martian equator
is between 15 and 47 kilometres thick.

Such a thin crust must contain a relatively high proportion of radioactive elements, which calls into question previous models of the chemical
composition of the entire crust.

Beneath the crust comes the mantle with the lithosphere of more solid rock reaching 400-600 kilometres down -- twice as deep as on Earth. This could
be because there is now only one continental plate on Mars, in contrast
to Earth with its seven large mobile plates. "The thick lithosphere fits
well with the model of Mars as a 'one-plate planet'," Khan concludes.



==========================================================================
The measurements also show that the Martian mantle is mineralogically
similar to Earth's upper mantle. "In that sense, the Martian mantle is
a simpler version of Earth's mantle." But the seismology also reveals differences in chemical composition. The Martian mantle, for example,
contains more iron than Earth's. However, theories as to the complexity
of the layering of the Martian mantle also depend on the size of the
underlying core -- and here, too, the researchers have come to new
conclusions.

The core is liquid and larger than expected The Martian core has a radius
of about 1,840 kilometres, making it a good 200 kilometres larger than
had been assumed 15 years ago, when the InSight mission was planned. The researchers were now able to recalculate the size of the core using
seismic waves. "Having determined the radius of the core, we can now
calculate its density," Sta"hler says.

"If the core radius is large, the density of the core must be relatively
low," he explains: "That means the core must contain a large proportion
of lighter elements in addition to iron and nickel." These include
sulphur, oxygen, carbon and hydrogen, and make up an unexpectedly large proportion. The researchers conclude that the composition of the entire
planet is not yet fully understood.

Nonetheless, the current investigations confirm that the core is liquid --
as suspected -- even if Mars no longer has a magnetic field.

Reaching the goal with different waveforms The researchers obtained
the new results by analysing various seismic waves generated by
marsquakes. "We could already see different waves in the InSight data,
so we knew how far away from the lander these quake epicentres were
on Mars," Giardini says. To be able to say something about a planet's
inner structure calls for quake waves that are reflected at or below
the surface or at the core. Now, for the first time, researchers have
succeeded in observing and analysing such waves on Mars.

"The InSight mission was a unique opportunity to capture this data,"
Giardini says. The data stream will end in a year when the lander's
solar cells are no longer able to produce enough power. "But we're far
from finished analysing all the data -- Mars still presents us with many mysteries, most notably whether it formed at the same time and from the
same material as our Earth." It is especially important to understand
how the internal dynamics of Mars led it to lose its active magnetic
field and all surface water. "This will give us an idea of whether
and how these processes might be occurring on our planet," Giardini
explains. "That's our reason why we are on Mars, to study its anatomy." ========================================================================== Story Source: Materials provided by ETH_Zurich. Note: Content may be
edited for style and length.


========================================================================== Journal References:
1. Amir Khan, Savas Ceylan, Martin van Driel, Domenico Giardini,
Philippe
Lognonne', Henri Samuel, Nicholas C. Schmerr, Simon C. Sta"hler,
Andrea C. Duran, Quancheng Huang, Doyeon Kim, Adrien Broquet,
Constantinos Charalambous, John F. Clinton, Paul M. Davis, Me'lanie
Drilleau, Foivos Karakostas, Vedran Lekic, Scott M. McLennan, Ross
R. Maguire, Chloe' Michaut, Mark P. Panning, William T. Pike,
Baptiste Pinot, Matthieu Plasman, John-Robert Scholz, Rudolf
Widmer-Schnidrig, Tilman Spohn, Suzanne E. Smrekar, William
B. Banerdt. Upper mantle structure of Mars from InSight seismic
data. Science, 2021; 373 (6553): 434 DOI: 10.1126/ science.abf2966
2. Simon C. Sta"hler, Amir Khan, W. Bruce Banerdt, Philippe Lognonne',
Domenico Giardini, Savas Ceylan, Me'lanie Drilleau, A. Cecilia
Duran, Raphae"l F. Garcia, Quancheng Huang, Doyeon Kim, Vedran
Lekic, Henri Samuel, Martin Schimmel, Nicholas Schmerr, David
Sollberger, E'le'onore Stutzmann, Zongbo Xu, Daniele Antonangeli,
Constantinos Charalambous, Paul M. Davis, Jessica C. E. Irving,
Taichi Kawamura, Martin Knapmeyer, Ross Maguire, Angela G. Marusiak,
Mark P. Panning, Cle'ment Perrin, Ana- Catalina Plesa, Attilio
Rivoldini, Ce'dric Schmelzbach, Ge'raldine Zenha"usern, E'ric
Beucler, John Clinton, Nikolaj Dahmen, Martin van Driel, Tamara
Gudkova, Anna Horleston, W. Thomas Pike, Matthieu Plasman, Suzanne
E. Smrekar. Seismic detection of the martian core. Science, 2021;
373 (6553): 443 DOI: 10.1126/science.abi7730
3. Brigitte Knapmeyer-Endrun, Mark P. Panning, Felix Bissig, Rakshit
Joshi,
Amir Khan, Doyeon Kim, Vedran Lekić, Benoit Tauzin, Saikiran
Tharimena, Matthieu Plasman, Nicolas Compaire, Raphael F. Garcia,
Ludovic Margerin, Martin Schimmel, E'le'onore Stutzmann, Nicholas
Schmerr, Ebru Bozdağ, Ana-Catalina Plesa, Mark A. Wieczorek,
Adrien Broquet, Daniele Antonangeli, Scott M. McLennan, Henri
Samuel, Chloe' Michaut, Lu Pan, Suzanne E. Smrekar, Catherine
L. Johnson, Nienke Brinkman, Anna Mittelholz, Attilio Rivoldini,
Paul M. Davis, Philippe Lognonne', Baptiste Pinot, John-Robert
Scholz, Simon Sta"hler, Martin Knapmeyer, Martin van Driel,
Domenico Giardini, W. Bruce Banerdt. Thickness and structure of
the martian crust from InSight seismic data. Science, 2021; 373
(6553): 438 DOI: 10.1126/science.abf8966 ==========================================================================

Link to news story: https://www.sciencedaily.com/releases/2021/07/210722163028.htm

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