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During the very first measurement of another planet’s core, seismography carried out over several Martian years revealed that the liquid metal core is softer than expected, more like a fluffy Mars than a Mars bar.
While the recently arrived Perseverance rover garnered much of the Mars-related attention, a trio of recently published papers that measured the depth and composition of the crust, mantle, and iron-nickel core of The Red Planet, written by the 2018 NASA InSight lander seeks to steal the show.
Using the same techniques of earth seismography, geoplanetary scientists examined data obtained from InSight’s extremely sensitive seismometer to measure a series of “March earthquakes.” The data they collected helps paint a picture of how Mars progressed from a planet that once had plenty of liquid water and a stable atmosphere thanks to its magnetic field, to a world of freezing temperatures and rust.
There were challenges, and in what National Geographic described as a major analytical feat, it’s worth mentioning what had to be overcome.
- On Earth, seismography is done with thousands of instruments placed in different areas. InSight has one.
- Without plate tectonics per se, the earthquakes on Mars are extremely weak and the strongest on record would barely be noticed by humans even if they were standing a few miles from the epicenter.
- Given the lack of additional instruments and weak shaking, InSight’s seismometer had to be extremely sensitive, so it also picks up wind readings, as well as crackles from minute molecular changes in the metal of the land. itself as it warms and cools down each Martian day.
- The most seismically active region on Mars was half a planet from the lander, and the planet’s core was blocking any readings that could have reached InSight.
A big plush
Thanks to all this, the team managed to obtain the dimensions of the planet’s core, the upper mantle and the Martian crust, all with an accuracy of a few kilometers.
“As a seismologist, you probably have one chance in your life to find a nucleus for a planet,” says Simon Stähler, member of InSight, a seismologist at ETH Zurich research university, in an interview with National Geographic.
Their main resources were P and S waves, the same two types of tremors that scientists measure on Earth and on the Moon. P waves move much like wind on water, pushing objects downward, while S waves vibrate and wiggle from side to side, dislodging particles as they move.
TO VERIFY: Discover incredible photos and listen to the Martian winds of the red planet, thanks to Perseverance Rover
These two waves travel through different types of matter, giving a sort of level of “length and height” granularity. P waves can travel through solids, liquids, and gases, while S waves can only travel through solids. Because P waves can pass through a solid mantle in a liquid nucleus, measuring their readings in a manner similar to sonar gives you an idea of the depth of the nucleus, while measuring the return velocity of the S wave gives you an idea. depth at which the nucleus begins, because it cannot pass through the liquid, and comes back bound to the surface.
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By measuring a set of P, S waves, and then a weaker delayed S wave a few hundred seconds later, the team determined that the Martian core is about 1,830 kilometers wide, slightly larger than expected. This means that unlike Earth, which has an upper mantle and a lower mantle, Mars only has one, about 500 kilometers deep.
“We deduced an average core density of 5.7 to 6.3 grams per cubic centimeter, which requires a substantial complement of light elements dissolved in the iron-nickel core,” write the authors, who published an article on each planetary layer, in the newspaper Science.
What this means
Believed to contain carbon, oxygen, hydrogen, and sulfur, this softer-than-expected core and monolayer lithosphere could shed light on the creation and demise of the Martian magnetosphere that took place ago. 3.7 billion years.
With a smaller lithosphere and a more porous core, convection currents would have created a potential for rapid cooling of the interior, which National Geographic assumes as the genesis of the Martian magnetosphere.
The loss of the magnetosphere would have caused the dissipation of the original Martian atmosphere. It is therefore essential to understand which planetary components may have led to this in order to understand why Mars lost all of its water and became a cold and rusty desert.
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Finally, by mapping in detail the Martian crust, which consists of two or three layers at a depth of between 24 and 72 kilometers, the team found that the heat-producing radioactive elements were 13 to 21 times more abundant than elsewhere. , which could help form a working theory on why Martian volcanoes appear where they do on a planet that does not have the plate tectonic forces that would normally create them.
The Red Planet reveals its secrets to us, forming a case study of planetary geosciences under totally different conditions from those on Earth, and expanding our understanding of the most interesting celestial bodies: the planets.
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