Mars2020 The 'rover' Perseverance prepares to collect the first samples from the surface
Martemania This is how the dream of colonizing the red planet advances
The
InSight
robot
cannot move. It is anchored to the surface of Mars but with its radars and other instruments it has taken the pulse of the red planet since the beginning of 2019, when it began to record the Martian earthquakes, called martemots. Now, several international teams present in three studies published simultaneously in the journal
Science
the analysis of the
in situ
measurements
made by this NASA probe that is allowing us to know what the interior of a planet other than Earth is like: its crust, its mantle and its core.
One of the aspects that most intrigued were the marsquakes, and
InSight
sensors
have been able to register a dozen, some of them originating below the Earth's crust.
The two larger ones appear to have originated in a region called Cerberus Fossae, a place where signs of seismic activity such as landslides had previously been detected.
An international team from the University of Cologne, Germany, and NASA, has used the seismic data collected by the probe to determine that
the crust of Mars at the point where the robot is located -Elysium Planitia- has a thickness between 20 and 39 kilometers.
As explained by the geophysicist at the University of Cologne Brigitte Knapmeyer-Endrun, leader of the study that has estimated the thickness of the crust, seismology can mainly measure contrasts in speed, which are the differences in the speed of propagation of seismic waves depending on the different materials that pass through: "We have the advantage that
the crust and the mantle are composed of different rocks,
so there is a marked speed jump between them. Based on these jumps in speed, the structure of the crust Mars can be determined very precisely. "
Multilayer bark
Under Elysium Planitia this team has found several layers, two safe and a possible third layer: "The first layer reaches a depth of 10 kilometers. Then there is another that lasts up to 20 km (with a margin of error +/- 5 km). What follows could already be the mantle, or another layer of the crust that would make it reach up to 39 kilometers deep ", clarifies Knapmeyer-Endrun in an email.
But with the data they currently have, he adds, they cannot distinguish if that third layer belongs to the crust or to the hand: "They are seismic waves and unfortunately it is not as simple as saying, 'We have three signals so there are three layers', because each of them can generate multiple signals since the waves can bounce in different directions within the layer several times. In our case, a multiple bounce from the 10 km deep layer could perfectly coincide in time with the signal from layer three ", so the existence of this third layer cannot be confirmed.
In either scenario, "says Knapmeyer-Endrun, they rule out the possibility that the entire crust is made of the same material. Their data suggests that the outermost layer is made up of porous rocks, which has come as a surprise.
However, if the third layer is not the crust and the mantle starts at 20 kilometers deep, it would mean that the Martian crust "is surprisingly thin, even compared to a continental crust like Earth's.
Below Colony, for For example, or in Spain, the earth's crust is about 30 kilometers thick "
, explains the German scientist.
Second self-portrait from 'InSight'
Also on Mars the thickness of the crust varies according to the place of the planet. "For example, it is thinner under the main basins and thicker under high volcanoes in the Tharsis region (eg Mount Olympus. Something similar happens on Earth. The thickness of the crust is almost zero at the ridges.
Mid-
oceanic
(
underwater elevations located in the middle part of the oceans), where new crust is being generated, while in the Himalayas it is about 80 kilometers deep. The principle looks a bit like an iceberg, the more crust protrudes in the top, the more there has to be underneath to make up for it, "he compares.
On Mars, they have used the absolute data from a particular location, the
InSight
work zone
where the crust is between 20 and 39 km thick, and combined it with information on gravity and topography to estimate the thickness of the crust across the planet.
Because there are different possible scenarios and uncertainties, they have established a thickness with
a range of 24 to 72 kilometers,
compared to the 110 kilometers that a previous study had calculated.
The researchers have combined the
InSight
data
with that collected by Martian orbiters such as the MRO.
Surprise at the core
Knowing the thickness of the crust of Mars is interesting for scientists because it arose in the early stages of the planet's formation, from the remains of a molten mantle, so that data on its current structure provides data on how this planet evolved, and with it, it helps them determine the differences with other worlds in the Solar System such as Earth.
Another team led by Amir Khan, from the University of Zurich, has used the seismic waves that have reached the surface after eight marsquakes to estimate the structure of the mantle, which would reach a depth of about 800 kilometers.
These researchers also argue that
the crust layer is rich in radioactive elements that produce heat
.
Finally, Simon Stähler, from the Swiss Institute of Technology in Zurich, leads the group that has investigated the Martian nucleus, which is relatively large, liquid and composed of metals, and whose radius they estimate at almost 1,830 kilometers.
According to their conclusions,
the mantle is formed by a rocky layer and not by two layers, as it happens on Earth.
This core, made up mostly of iron and nickel, is less dense than previously thought because it is enriched with lighter elements.
Marsmots
As far as marsquakes are concerned, the investigation is ongoing but there are already some things that have been found out. The seismograms that
InSight
has provided
,
says Knapmeyer-Endrun, "resemble those of tectonic earthquakes, and there seems to be a similar mechanism behind them. Mars does not have tectonic plates, which on Earth generate most earthquakes, but they do I expected it to be seismically active at least due to cooling (the planet radiates heat into space and contracts as it cools, causing stresses in the crust that could trigger earthquakes). The people on the
InSight
science team
he is currently investigating how the location of these earthquakes is linked to geological structures to understand the tectonics of Mars.
However, there are other types of earthquakes in which it seems that the waves only bounce off a layer within the crust, "he says.
In an independent commentary also published in
Science
, Sanne Cottaar and Paula Koelemeijer state that "direct seismic observations on Mars represent a breakthrough in planetary seismology, and as more earthquakes are measured, scientists will refine these models of the red planet."
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