If you want to do a forensic study of the Solar System, you can head to the main asteroid belt between Mars and Jupiter. This is where you can find ancient rocks from the early days of the Solar System. In the cold vacuum of space, far away from the Sun, asteroids are largely insulated from space weathering.
Space scientists sometimes refer to asteroids – and their meteorite fragments that fall to Earth – as time capsules because of the evidence they have.
The asteroid Psyche is particularly interesting, and NASA is sending a mission to investigate the unusual part of the rock.
Prior to that mission, a team of researchers combined observations of Psyche from an array of telescopes and produced a map of the asteroid’s surface.
Astronomers divide asteroids into three categories. Carbonaceous or C-type asteroids are the most common type. They make up about 75 percent of known asteroids and contain large amounts of carbon. Carbon darkens them, and they have a low albedo.
Silicaceous or S-type asteroids are the second most common type. They make up about 17 percent of known asteroids and are mostly composed of iron and magnesium silicates.
Metallic or M-type asteroids are the rarest type of asteroid and account for about 8 percent of known asteroids. They appear to be more metallic than other asteroid types, and scientists think they are the source of iron meteorites that fall to Earth. M-type 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 has a diameter of about 220 kilometers (140 mi). It is called 16 Manas because it was the 16th minor planet discovered. (Large asteroids like Psyche are also called minor planets.)
(NASA/JPL-Caltech/ASU)
Psyche is sometimes called a ‘gold-mine asteroid’ because of its wealth of iron and nickel. Although to be clear, no one thinks it is rich in gold.
Visible light images of the psyche don’t tell us much. The European Southern Observatory’s VLT took some pictures of the asteroid, but did not provide any details.
The history of the psyche is a history of uncertainty. For a long time, astronomers thought it was the open iron core of a much larger body. In this hypothesis, a powerful collision or series of collisions stripped the body’s crust and mantle.
The larger body would have been completely ejected and measured something like 500 km (310 mi) in diameter. With the crust and mantle gone, only the iron-rich core was left.
The idea fell out of favor as time went on, and astronomers continue to look into it. Evidence showed that it was not dense enough to be solid iron and is probably porous.
Other researchers suggested that Manas was somehow disrupted and then re-deposited as a mixture of metals and silicates. One study indicates that Manas is not as metal-rich as was thought and is more of a pile of rubble. In that scenario, a collision with the more common C-type asteroids deposited a layer of carbon and other materials on the surface of Psyche.
The most fascinating idea behind the origin of Psyche is the ferro-volcanic idea. A 2019 study offered evidence that Manas was once a molten blob. In that scenario, the outer layers cooled and formed stress cracks, and the buoyant molten core erupted to form iron volcanoes.
The only way to know for sure what a psyche is, is to go and see it. So that’s what NASA is doing.
The mission is called Psyche and is scheduled to launch sometime in the fall of 2022. The spacecraft will rely on solar-electric propulsion and gravity-assist maneuvers with Mars to reach Manas in 2026.
It will spend 21 months studying the asteroid and will follow four different orbital paths, each one closer after the other than the last.
An illustration of the Psyche probe near the Manas asteroid. (NASA/JPL-Caltech/ASU)
As it moves closer to the asteroid, it will focus on various scientific purposes.
To help prepare for the mission, a team of researchers created a new map of Psyche’s surface.
The map is in a paper published in Journal of Geophysical Research: Planets, The title is “Asteroid’s Heterogeneous Surface (16) Psyche”, and the lead author is Saverio Cambioni from 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 an evolving surface, and these maps confirm that metal-rich asteroids are interesting enigmatic worlds. It’s another reason to wait for the Psyche mission to the asteroid.”
In this study, the authors used the Atacama Large Millimeter/submillimeter Array (ALMA) to better visualize 16 manas. ALMA 66 is a radio telescope composed of a high-precision antenna. The separate antennae work together as an interferometer with a high resolution.
ALMA works on temperature-sensitive wavelengths and certain electrical properties of materials on the surface of Manus.
“The signals from the ALMA antennas can be combined into a synthetic signal that is equivalent to a telescope with a diameter of 16 kilometers (10 miles),” said co-author Catherine de Clare, assistant professor of planetary science and astronomy at Caltech. “The bigger the telescope, the higher the resolution.”
The new map is based on two types of measurements. One is thermal inertia, which is how long it takes a material to reach the temperature of its environment. Higher thermal inertia means it takes 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 conducts poorly and is a good insulator and vice versa.
The researchers took ALMA observations of thermal inertia and dielectric constants and ran hundreds of simulations to see which combinations of materials could explain them. “We ran these simulations field by field so that we could capture differences in surface properties,” Cambioni says.
Pure iron has infinite dielectric constant. By measuring the dielectric constant on Manas, researchers can map the surface and locate areas rich in iron. Iron also has high thermal inertia because it is very dense.
So a combination of thermal inertia and dielectric constant measurements gives a good idea of which surface areas on Manas are rich in iron and other metals.
Researchers call Psych the Bravo—a curious feature on the golf field. That region has systematically lower thermal inertia than the highland regions. The Bravo-Golf Sphere is the depression to the right of the asteroid’s prime meridian in the image below.
Why is there less thermal inertia in low altitude region? Other studies show that this region is also radar-bright. Why so? The researchers came up with three possibilities.
The lowlands may be rich in metal, but are covered with fine, porous regolith which reduces their thermal inertia compared to the highlands covered with coarse regolith. Thermal inertia increases with particle size. In this scenario, fine-grained regolith would have accumulated in the lowlands.
“Pounds of finer-grained material have been observed on smaller asteroids whose gravity is low enough to move the surface and pool finer material,” Cambioni said. “But the psyche is one large body, so if the fine-grained material accumulates at the bottom of the depression, 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 as the rock porosity increases. Impact fractures can make lowlands more porous.
The third hypothesis is that the lowlands contain more silicate-rich material than the highlands, giving them a lower dielectric constant than some regions of the highlands. The idea is that the Bravo-Golf depression may have formed from the impact of a silicate-rich impactor and leaves behind a silicate-rich residue.
Altogether, the study shows that the surface of 16 Manas is covered with a variety of materials. It also adds to other evidence indicating that the asteroid is metal-rich, although the abundance of metals and silicates varies greatly in different regions.
It also suggests that the asteroid may be the remnant core of a differentiated body that lost its mantle and crust long ago.
“In conclusion, we provide evidence that Psyche is a metal-rich asteroid whose surface is heterogeneous, shows both metallic and silicate material, and evolved from impacts,” conclude the authors.
Simone Marchi is a staff scientist at the Southwest Research Institute and a co-investigator on NASA’s Psyche mission. Marchi was not involved in the study, but he commented on its importance in a press release. “These data suggest that the surface of Psyche is heterogeneous, with potentially notable 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 spectrometers and a color imager. So, the possible presence of structural abnormalities is something the Psyche Science team is eager to study more.”
Confirming these findings more rigorously would be up to NASA’s Psyche mission.
But to understand this in more detail, sending a spacecraft to Psyche is about more than just Psyche.
If Psyche is the remnant core of a rocky, differentiated planet, it would reveal something about our planet and how the individual bodies formed. Would it have some of the same light elements that we expect are at the core of the Earth? Earth’s core is not dense enough to contain pure iron and nickel. Scientists think that it consists of lighter elements such as sulphur, silicon, oxygen, carbon and hydrogen.
The Psyche mission will also determine whether the asteroid formed under more oxidizing or more reducing conditions than in Earth’s core. It will tell us more about solar nebulae and protoplanetary disks.
People sometimes refer to Manas as a gold mine asteroid because it is so metal-rich. There is an enormous amount of iron in the shape of an object, although that value is unlikely to be attained or accessible any time soon.
But if knowledge is as valuable as iron, 16 manas can still be a gold mine.
This article was originally published by Universe Today. Read the original article.
