Astronomers reveal the most detailed map of the asteroid Psyche yet

Astronomers at MIT and elsewhere have mapped the composition of the asteroid Psyche, and revealed a surface of metal, sand and rock.
Enlarge / Astronomers at MIT and elsewhere have mapped the composition of the asteroid Psyche, and revealed a surface of metal, sand and rock.


Astronomers have produced the most detailed map to date of the surface of 16-Psyche, an asteroid that scientists believe may have clues to how planets were formed in our solar system. According to an article published in the Journal of Geophysical Research, 16-Psyche has a very varied surface of metal, sand and rock which suggests that history may include metallic eruptions, in addition to being hit by other celestial bodies. The asteroid is in focus for NASA’s Psyche mission, which will be launched later this year.

As we have reported before, 16 Psyche is an M-type asteroid (meaning it has a high metal content) orbiting the sun in the main asteroid belt, with an unusual potato-like shape. The long-standing preferred hypothesis is that Psyche is the exposed metallic core of a protoplanet (planetesimal) from the earliest days of our solar system, with the crust and mantle removed by a collision (or multiple collisions) with other objects. In recent years, researchers have concluded that the mass and density estimates do not correspond to a completely metallic residual core. Rather, it is more likely a complex mixture of metals and silicates.

Alternatively, the asteroid may once have been a superior body for a particular class of rocky iron meteorites, one that broke up and resurfaced in a mixture of metal and silicate. Or maybe it’s an object like 1 Ceres, a dwarf planet in the asteroid belt between the orbits of Mars and Jupiter – except that 16 Psyche may have experienced a period of iron volcanism as it cooled, leaving highly enriched metals in these volcanic centers.

Scientists have long suspected that metallic nuclei lurk deep inside terrestrial planets such as Earth. But these cores are buried too far under rocky mantles and crusts for scientists to find out. As the only metallic nucleus-like body discovered, Psyche provides the perfect opportunity to shed light on how the rocky planets of our solar system (Earth, Mercury, Venus and Mars) may have been formed. NASA approved the Psyche mission in 2017, and intended to send a spacecraft to orbit the asteroid and collect important data about its properties.

To the left, the map shows surface properties of Psyche, from sandy areas (purple / low) to rocky areas (yellow / high). The map to the right shows the metal abundance on Psyche, from low (purple) to high (yellow).

Previous mapping efforts depended on measuring infrared light bouncing from the asteroid’s surface with various telescopes around the world. Last year, astronomers produced a much higher resolution surface map of Psyche, based on observational data from 2019 collected from all 66 radio antennas of the Atacama Large Millimeter / Submillimeter Array (ALMA) in Chile.

By combining all these signals into a single synthetic signal, the team achieved the corresponding resolution of a telescope with a diameter of 16 kilometers (10 miles) – about 20 miles per pixel. This view enabled them to solve many compositional variations on the asteroid’s surface. They used this to create a thermal emission map of the asteroid’s surface and a high-resolution 3D model of Psyche.

This latest map is based on hundreds of computer-simulated scenarios, each with a different combination of surface material composition, taking into account the asteroid’s rotation. The team then compared these simulations with the actual thermal emissions in the ALMA data to determine the most likely map of the 16-Psyche surface.

The results: The asteroid is rich in metals, but the distribution varies across the surface. A similarly varied distribution of silicates suggests that 16-Psyche may once have had a silicate-rich mantle. Furthermore, the material at the bottom of the crater changes temperature faster than along the edge when the asteroid rotates. The authors suggest that these craters may have deposits (“ponds”) of fine-grained sand. This is somewhat surprising given the mass of 16-Psyche and its stronger gravity, compared to smaller asteroids that have fine-grained materials.

“These data indicate that Psyche’s surface is heterogeneous, with possible notable variations in composition,” said Simone Marchi of the Southwest Research Institute, a co-investigator on the Psyche mission who was not involved in the current study. “One of the main 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. The possible presence of compositional heterogeneities is something that the Psyche Science Team is eager to study more.”

DOI: Journal of Geophysical Research, 2022. 10.1029 / 2021JE007091 / a> (About DOIer).