Astronomers unveil the most detailed map yet of the metal-asteroid psyche

If you want to do a forensic study of the solar system, you can head to the main asteroid belt between Mars and Jupiter. There you will find ancient rocks from the beginning of the solar system. Out there in the cold vacuum of space, far from the Sun, asteroids are largely unaffected by space weathering.

Space scientists sometimes refer to asteroids — and their meteorite fragments that fall to Earth — as time capsules because of the evidence they contain.

Asteroid Psyche is particularly interesting, and NASA is sending a mission to study the unusual boulder.

Ahead of this mission, a team of researchers combined observations of Psyche with a series of telescopes and created a map of the asteroid’s surface.

Astronomers divide asteroids into three categories. Carbonaceous asteroids or C-type asteroids are the most common type. They make up about 75 percent of known asteroids and contain large amounts of carbon. The carbon makes them dark and they have a low albedo.

Silica or S-type asteroids are the second most common type. They make up about 17 percent of all known asteroids and mostly consist of iron and magnesium silicates.

Metal or M-type asteroids are the rarest types of asteroids, accounting for about 8 percent of known asteroids. They appear to contain more metal than the other asteroid types, and scientists believe they are the source of iron meteorites that fall to Earth. Type M meteorites were one of the earliest sources of iron in human history.

Psyche (16 Psyche) is an M-type asteroid. It is also called a dwarf planet because it is about 220 kilometers in diameter. It is referred to as 16 Psyche because it was the 16th discovered minor planet. (Larger asteroids like Psyche are also known as minor planets.)


Psyche is sometimes called the “gold-mining asteroid” because it is rich in iron and nickel. To be clear, no one thinks it’s gold rich.

Visible slides of Psyche don’t tell us much. The European Southern Observatory’s VLT took some pictures of the asteroid, but they didn’t reveal any details.

The history of the psyche is a history of uncertainty. Astronomers have long thought it to be the exposed iron core of a much larger body. In this hypothesis, a strong collision or series of collisions stripped the body’s crust and mantle.

The larger body would be fully differentiated and about 500 km (310 miles) in diameter. After the crust and mantle disappeared, only the iron-rich core remained.

This idea fell out of favor over time and astronomers continued to monitor it. Evidence showed it was not dense enough to be solid iron and is likely porous.

Other researchers suggested that Psyche was somehow disrupted and then re-enriched as a mixture of metals and silicates. A study showed that psyche is not as metal-rich as mind and is more of a shambles. In this scenario, collisions with more common C-type asteroids deposited a layer of carbon and other materials on Psyche’s surface.

The most exotic idea behind Psyche’s origins is the Ferrovolcan idea. A 2019 study presented evidence that Psyche was once a molten blob. In this scenario, the outer layers cooled and stress cracked, and the floating molten core erupted as iron volcanoes.

The only way to know for sure what Psyche is is to go and see it. So that’s what NASA does.

The mission is called Psyche and is scheduled to launch sometime in fall 2022. The spacecraft will rely on solar-electric propulsion and gravity-assisted maneuvers with Mars to arrive at Psyche in 2026.

It will spend 21 months studying the asteroid, following four separate orbits, each closer than the previous one.

An illustration of the Psyche probe near the Psyche asteroid. (NASA/JPL-Caltech/ASU)

As it gets closer to the asteroid, it will focus on other science targets.

A team of researchers created a new map of Psyche’s surface in preparation for the mission.

The map is published in a paper in the Journal of Geophysical Research: Planets. The title is The Heterogeneous Surface of Asteroid (16) Psyche, and the lead author is Saverio Cambioni of MIT’s Department of Earth, Atmospheric and Planetary Sciences (EAPS).

“The surface of Psyche is very heterogeneous,” Cambioni said in a press release. “It’s a developed surface, and these maps confirm that metal-rich asteroids are interesting enigmatic worlds. This is another reason to look forward to the Psyche mission to this asteroid.”

In this study, the authors used the Atacama Large Millimeter/submillimeter Array (ALMA) to get a better look at 16 psyche. ALMA is a radio telescope consisting of 66 high-precision antennas. The separate antennas work together as a high resolution interferometer.

ALMA operates at wavelengths sensitive to temperature and some electrical properties of materials on Psyche’s surface.

“The signals from the ALMA antennas can be combined into a synthetic signal equivalent to a telescope 16 kilometers (10 miles) across,” said co-author Katherine de Kleer, assistant professor of planetary science and astronomy at Caltech. “The larger the telescope, the higher the resolution.”

The new map is based on two types of measurements. One of them is thermal inertia, which is the time it takes for a material to reach the temperature of its surroundings. Higher thermal inertia means it lasts longer.

The second is the dielectric constant. The dielectric constant describes how well a material conducts heat, electricity or sound. A material with a low dielectric constant is a poor conductor and a good insulator and vice versa.

Researchers used ALMA’s thermal inertia and dielectric constant observations and ran hundreds of simulations to see which material combinations could explain them. “We ran these simulations area by area to detect differences in surface properties,” says Cambioni.

Pure iron has an infinite dielectric constant. By measuring the dielectric constant on Psyche, the researchers were able to map the surface and locate regions richer in iron. Iron also has a high thermal inertia because it is so dense.

So the combination of thermal inertia and dielectric constant measurements gives a good idea of ​​which surface regions on Psyche are rich in iron and other metals.

The researchers call a strange feature on Psyche the Bravo Gulf region. This region has a systematically lower thermal inertia than the highland regions. The Bravo Gulf region is the depression directly to the right of the asteroid’s Prime Meridian in the image below.

Why does a low area have less thermal inertia? Other studies show that the region is also radar bright. Why is that? The researchers came up with three possibilities.

The lowlands may be metal-rich but covered with fine, porous regolith that reduces its thermal inertia compared to the coarser regolith-covered highlands. Thermal inertia increases with particle size. In this scenario, fine-grained regolith would have accumulated in the lowlands.

“Ponds of fine-grained material have been seen on small asteroids whose gravity is low enough for impacts to shake the surface and collect finer materials,” Cambioni said. “But Psyche is a big body. So if fine-grained material has accumulated at the bottom of the well, that’s interesting and somewhat mysterious.”

The second hypothesis is that the surface material covering the lowlands is more porous than the highlands. The thermal inertia decreases with increasing porosity of the rock. Impact fractures could also make the lowlands more porous.

The third hypothesis is that the lowlands have more siliceous materials than the highlands, giving them a lower dielectric constant than some areas of the highlands. The idea is that the Bravo Gulf depression could have been formed by impact with a siliceous impactor and would have left siliceous residues.

Overall, the study shows that the surface of 16 Psyche is covered with a variety of materials. It also adds to other evidence showing that the asteroid is rich in metals, although abundances of metals and silicates vary significantly in different regions.

It also suggests the asteroid could be a remnant of a differentiated body that lost its mantle and crust long ago.

“In conclusion, we provide evidence that Psyche is a metal-rich asteroid with a heterogeneous surface, containing both metal and silicate materials, and appears to have evolved through impacts,” the authors conclude.

Simone Marchi is a Research Associate at the Southwest Research Institute and a co-investigator on NASA’s Psyche mission. Marchi was not involved in this study but commented on its importance in a press release. “These data indicate that the surface of Psyche is heterogeneous, with possible notable variations in composition. One of the main goals of the Psyche mission is to study the composition of the asteroid’s surface using its gamma-ray and neutron spectrometer and a color imager. So, the possible presence of compositional heterogeneity is something the Psyche Science team is keen to investigate further.”

It’s up to NASA’s Psyche mission to confirm these results more rigorously.

But sending a spaceship all the way to Psyche to get a better understanding of it means more than just Psyche herself.

If Psyche is the remaining core of a rocky, differentiated planetesimal, it will reveal something about our planet and how differentiated bodies form. Will it contain some of the same light elements we expect to find in Earth’s core? The core of the earth is not dense enough to consist of pure iron and nickel. Scientists believe it contains lighter elements like sulfur, silicon, oxygen, carbon and hydrogen.

The Psyche mission will also determine whether the asteroid was formed under more oxidizing or more reducing conditions than Earth’s core. This will tell us more about the solar nebula and the protoplanetary disk.

People sometimes refer to Psyche as the gold mining asteroid because it is so metal rich. An object of its size would contain an enormous amount of iron, although this value is unlikely to be realized or accessible anytime soon.

But if knowledge is as valuable as iron, then 16 Psyche could still be a gold mine.

This article was originally published by Universe Today. Read the original article.