2023-10-12 13:55:12
The new mission Psyche de la NASA will orbit, map and study in enormous detail one of the most desired objects in space exploration these days: the metallic asteroid cataloged as (16) Psyche. However, its value goes beyond its enormous metallic mass, estimated at around twenty thousand billion tons.
The word asteroid already gives clues about these bodies that Psyche represents. Is about rocky, metal-rocky or metallic bodies that tend to move elusively through the star fields of our telescopes.
Due to the distance at which they are found and their relatively small size, we cannot see their apparent diameter through a telescope and, therefore, they have a stellar appearance. If it were not for the fact that they move in their orbit around the Sun and move with respect to the background of fixed stars, we would practically not notice its presence. Hence, visiting them is the only option to collect countless and valuable information about their nature and their past.
Among all of them, it is not a whim to choose Psyche. We are looking at an asteroid about 200 km in diameter, a true treasure rich in metals and, probably, other resources. But Psyche is also very important from a “cosmogonic” point of view, because we may be looking at a naked planetary embryo that teaches us how the planets evolve.
Planetary embryos
There are many open questions in our current knowledge about the origin and evolution of metallic asteroids.
If our formation theories are correct, at the beginning of the solar system there were dozens of planetary embryos and only a few survived to form the terrestrial planets.
Originally, the largest planetary bodies accumulated radioactive elements, such as Al-26 and Fe-60. These isotopes progressively disintegrated and the heat generated was retained, melting the formative materials. In that high temperature past they differentiated internally and the denser metals sank into the core. The vast majority of these embryos were destroyed by colossal impacts during the very harsh phase of accretion end of the planets: the hierarchical accretion.
We know, for example, that a Mars-sized embryo collided with Earth and that the material that resulted from the impact gave origin to the Moon. Other impacts were catastrophic, destroying the embryos but creating large fragments that we find in the earth today. main asteroid belt (between Mars and Jupiter).
In these large surviving asteroids, the subsequent hammering of colossal impacts caused them to lose their crust and a good part of the mantle, leaving their cores, rich in iron and nickel, exposed and forming the current purely metallic asteroids. We think that (16) Psyche is one of them.
Understanding its nature is also relevant for aspects related to planetary defense. Some of the impact craters we know of, such as the famous Barringer crater (Meteor Crater), were excavated by metallic asteroids, much more resistant to penetrating the atmosphere at hypervelocity and, therefore, capable of excavating large craters.
The Heavy Metal Mission
Some years ago, a group of European astrophysicists and planetary scientists, among whom I was representing the Institute of Space Sciences (CSIC)we try to European Space Agency (ESA) bet on a space mission to a metallic asteroid. The mission had an unforgettable name: Heavy Metal. She was shortlisted twice and we were close to making a visit to a metallic asteroid a reality, but she was ultimately ruled out.
Soon we knew that the die was cast: NASA would once again take the reins and get ahead of Europa, making the Psyche mission a reality.
Now it will be NASA who will demonstrate whether the asteroid Psyche is the remnant of a planetary core.
Evidence of its origin as a planetary embryo
To confirm that Psyche is what we believe, she must retain properties consistent with her past. We find the clues in the meteorites that we already know.
Metallic meteorites arrive to Earth highly magnetized, and the process of chemical segregation (when they melt due to the heat of the radioactive decay of their original components) tends to create highly magnetic nuclei.
On the other hand, given the enormous collisions that would explain the exposure of its metallic core, the surface of Psyche must have been sculpted into gigantic craters that could also have affected that primitive paleomagnetism.
The diversity of metal-rich, or even metal-locose, meteorites that have reached Earth also allows us to exemplify the nature of Psyche that remains to be revealed.
Purely metallic meteorites are alloys of iron and nickel in different proportions. When cut, polished and treated properly they show a structure that reveals the famous Widmanstätten lines, produced by taenite and camacite crystals. These unique crystalline structures are produced by cooling rates of around 1º C per million years. This tells us that it must come from a planetary core large enough to cool so slowly and, on the other hand, that we will not be able to create them in a laboratory.
NASA’s Psyche mission
The Psyche mission technology It will be a huge advance in our understanding of metallic asteroids. When it reaches its goal in 2029, it will have 26 months of very interesting experiments ahead of it thanks to its various instrumentation.
The spacecraft’s magnetometer will look for evidence of paleomagnetismo, that is, ancient magnetic fields. The existence of paleomagnetism would demonstrate that the asteroid was formed from the core of a planetary body.
The orbiter’s gamma ray and neutron spectrometer will make it possible to identify the chemical elements that make it up. This will be complemented with a hyperspectral imaging camera that will elucidate the mineral composition of Psyche, as well as its topography. The high resolution of these images will allow the surface structures to be resolved in great detail, which will help to better understand the early history of that asteroid.
An exciting part of the mission is the one in which the telecommunications system will be used to investigate the gravitational field. This will be done by analyzing the propagation of the radio waves with which the spacecraft communicates, which will allow us to verify whether the asteroid Psyche affects the orbit of the spacecraft.
As a whole, the determination of the mass, shape, rotation and gravity field will allow us to better understand the geology of the surface, its composition and internal structure.
An ingenuity to propel yourself
The Psyche probe will also use a novel system to travel the distance to the asteroid. It will be powered by propellants based on the Hall effect, a solar electric propulsion system that will transform the energy of its large solar panels to create electric and magnetic fields. These, in turn, accelerate and expel charged atoms – or ions – of a propellant called xenon – a neutral gas used in car headlights and plasma televisions – at such a high speed that it creates enough thrust to move the vehicle. huge ship.
The Psyche mission is essential to determine if the asteroid is composed of homogeneous metal, an alloy of iron and nickel similar to the metallic meteorites that we know – the Meteoritic Society to which I belong has cataloged 1,982 metal-rich meteorites as we can see in the updated catalog known as Meteoritical Bulletin– or if it also contains rocky materials, the result of the materials implanted in that collisional landscaping phase that presumably exposed its metal core.
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Whatever the results, we should be happy that missions like this see the light of day. The exploration of asteroid Psyche will revolutionize our understanding of both the origin and evolution of metallic asteroids and the formation of rocky planets, including Earth.
Go Psyche!
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