Astronomers Unveil The Most Detailed Map of The Metal Asteroid Psyche Yet

The major asteroid belt between Mars and Jupiter is a good place to start if you want to perform a forensic investigation of the Solar System. There are old rocks from the Solar System's early days can be found there. Asteroids are virtually unaffected by space weathering out there in the frigid vacuum of space, far from the Sun.

Because of the evidence they contain, asteroids — and their meteorite bits that fall to Earth – are frequently referred to as time capsules by space scientists.

The asteroid Psyche is particularly intriguing, and NASA has dispatched a spacecraft to explore the strange object.

A team of experts used views of Psyche from a variety of observatories to create a map of the asteroid's surface in anticipation of the expedition.

Asteroids are classified into three groups by astronomers. Carbonaceous asteroids, sometimes known as C-type asteroids, are the most frequent. They account for around 75% of all known asteroids and contain a lot of carbon. They are black because of the carbon, and their albedo is poor.

The second most frequent class of asteroids is silicaceous or S-type asteroids. They account for around 17% of all known asteroids and are mostly composed of iron and magnesium silicates.

Metal asteroids, often known as M-type asteroids, are the rarest asteroids, accounting for just 8% of all known asteroids. They appear to be heavier than other asteroid varieties, and experts believe they are the source of iron meteorites that fall to Earth. M-type meteorites were one of humanity's earliest sources of iron.

Psyche (16 Psyche) is an asteroid of the M class. It's also known as a dwarf planet since its diameter is just approximately 220 kilometers (140 miles). It is known as 16 Psyche since it was found as the 16th minor planet. (Major asteroids, like as Psyche, are also referred to as minor planets.)

Because of its abundance of iron and nickel, Psyche is frequently referred to as the 'Gold-mine Asteroid.' To be clear, no one believes it is gold-rich.

Psyche's visible light photos don't reveal anything. The asteroid was photographed by the European Southern Observatory's VLT, but no details were revealed.

The history of Psyche is one of ambiguity. Astronomers assumed it was the exposed iron core of a much bigger planet for a long time. According to this theory, the body's crust and mantle were taken away by a violent impact or series of collisions.

The bigger body would have been fully differentiated, with a diameter of around 500 kilometers (310 miles). Only the iron-rich core remained after the crust and mantle were destroyed.

As time passed, that theory went out of favor, but astronomers continued to observe it. It wasn't dense enough to be solid iron, and it's most likely porous, according to the evidence.

Others hypothesized that Psyche was disturbed and then re-accreted as a combination of metals and silicates. According to one research, Psyche isn't as metal-rich as previously assumed and is more of a jumble. Collisions with more common C-type asteroids would deposit a coating of carbon and other components on Psyche's surface under such scenario.

The Ferro-volcanic theory is the most exotic theory regarding Psyche's genesis. According to a 2019 research, Psyche was once a molten blob. The outer layers cooled and created stress cracks in such scenario, while the buoyant molten core erupted as iron volcanoes.

The only way to know for certain what Psyche is is to examine it. That is exactly what NASA is doing.

Psyche is the name of the mission, and it will launch in the fall of 2022. To reach Psyche in 2026, the spacecraft will use solar-electric propulsion and a gravity-assist maneuver with Mars.

It will explore the asteroid for 21 months, taking four different orbital trajectories, each one getting closer to the preceding one.

As it approaches the asteroid, it will concentrate on several scientific goals.

To aid in the mission's preparation, a team of researchers created a fresh map of Psyche's surface.

The map was published in the Journal of Geophysical Research: Planets as part of a publication. Saverio Cambioni of MIT's Department of Earth, Atmospheric, and Planetary Sciences is the principal author of "The Heterogeneous Surface of Asteroid (16) Psyche" (EAPS).

"Psyche's surface is very heterogeneous," Cambioni stated in a press statement. "It's an evolved surface, and these maps confirm that metal-rich asteroids are interesting enigmatic worlds. It's another reason to look forward to the Psyche mission going to the asteroid." 

The Atacama Large Millimeter/submillimeter Array (ALMA) was employed in this investigation to get a better look at 16 Psyche. ALMA is a radio telescope with 66 very precise antennas. The individual antennas work together as a high-resolution interferometer.

ALMA works at wavelengths that are sensitive to Psyche's surface temperature and some electric characteristics.

"The signals of the ALMA antennas can be combined into a synthetic signal that's equivalent to a telescope with a diameter of 16 kilometers (10 miles)," said Katherine de Kleer, an assistant professor of planetary science and astronomy at Caltech, who was not involved in the research. "The larger the telescope, the higher the resolution." 

The new map is based on two different sources of data. Thermodynamic inertia is the time it takes for a substance to attain the temperature of its surroundings. It takes longer when the thermal inertia is higher.

The dielectric constant is the second. The dielectric constant is a measurement of a material's ability to transmit heat, electricity, or sound. A low dielectric constant substance transmits poorly yet is an excellent insulator, and vice versa.

The researchers used the ALMA thermal inertia and dielectric constant findings to run hundreds of simulations to explore which material combinations may explain them. "We ran these simulations area by area so we could catch differences in surface properties," Cambioni explains.

The dielectric constant of pure iron is unlimited. The researchers were able to map the surface of Psyche and pinpoint places richer in iron by measuring the dielectric constant. Because iron is so thick, it has a high thermal inertia.

Combining thermal inertia and dielectric constant data provides a fair indication of which Psyche surface areas are rich in iron and other metals.

The Bravo-Golf area is a strange feature on Psyche, according to the experts. The thermal inertia of such region is consistently lower than that of the highlands. In the figure below, the Bravo-Golf area is the depression close to the right of the asteroid's prime meridian.

Why does a low-elevation location have less thermal inertia than a higher-elevation area? According to other research, the area is similarly radar-bright. What is the reason behind this? Three alternatives were proposed by the researchers.

The lowlands may be metal-rich, but they are covered with thin, porous regolith, which has a lower thermal inertia than the highlands, which are covered in coarser regolith. The thermal inertia of a particle rises with its size. Finer-grained regolith would have accumulated in the lowlands in this scenario.

"Ponds of fine-grained materials have been seen on small asteroids, whose gravity is low enough for impacts to shake the surface and cause finer materials to pool," Cambioni explained. "But Psyche is a large body, so if fine-grained materials accumulated on the bottom of the depression, this is interesting and somewhat mysterious."

The second theory is that the lowlands' surface material is more permeable than the highlands'. As rock porosity rises, thermal inertia reduces. Impact cracks may also increase the porousness of the lowlands.

The third theory is that the lowlands contain more silicate-rich minerals than the highlands, resulting in a lower dielectric constant in some highland places. The theory is that the Bravo-Golf depression was produced by an impact with a silicate-rich impactor, which left behind silicate-rich residue.

Overall, the investigation reveals that the surface of 16 Psyche is coated in a wide range of materials. It also adds to existing evidence indicating the asteroid is metal-rich, however the amount of metals and silicates varies greatly over the asteroid's surface.

It also implies that the asteroid might be the core of a differentiated body that has long since lost its mantle and crust.

"In conclusion, we provide evidence that Psyche is a metal-rich asteroid whose surface is heterogeneous, shows both metal and silicate materials, and appears evolved by impacts," the authors write.

Simone Marchi is a Southwest Research Institute staff scientist and a co-investigator on NASA's Psyche project. Marchi wasn't a part of the research, although he did comment on its relevance in a news release. "These data show that Psyche's surface is heterogeneous, with possible remarkable variations in composition. One of the primary goals of the Psyche mission is to study the composition of the asteroid surface using its gamma rays and neutron spectrometer, and a color imager. So, the possible presence of compositional heterogeneities is something that the Psyche Science Team is eager to study more."

NASA's Psyche mission will have to validate these conclusions more thoroughly.

However, sending a spacecraft all the way to Psyche in order to better comprehend it is about more than simply Psyche.

If Psyche is the residual core of a rocky, differentiated planetesimal, it will offer information about our planet and the formation of differentiated bodies. Will it have some of the same light components as the Earth's core, as we expect? The Earth's core is too thin to be made entirely of iron and nickel. It is thought to contain lighter components such as sulfur, silicon, oxygen, carbon, and hydrogen, according to scientists.

The Psyche mission will also see if the asteroid developed in more oxidizing or reducing circumstances than Earth's core. This will provide further information about the solar nebula and protoplanetary disk.

Because of its abundance of metals, Psyche is frequently referred to as the Gold Mine Asteroid. The quantity of iron contained in an item of this size would be immense, but that value is unlikely to be recognized or accessible anytime soon.

If information is worth as much as iron, though, 16 Psyche might still be a gold mine.