Astronomers at MIT and elsewhere have mapped the composition of asteroid Psyche, revealing a surface of metal, sand, and rock. Credit: Screenshot courtesy of NASA
The varied surface of asteroid Psyche suggests a dynamic history, which could include metallic eruptions, asteroid-shaking impacts, and a lost rocky mantle.
Later this year,
This illustration, updated in April 2022, depicts NASA’s Psyche spacecraft. Set to launch in August 2022, the Psyche mission will explore a metal-rich asteroid of the same name that lies in the main asteroid belt between Mars and Jupiter. The spacecraft will arrive in early 2026 and orbit the asteroid – also shown in this illustration – for nearly two years to investigate its composition. Credit: NASA/JPL-Caltech/ASU
Overall, Psyche’s surface was found to be surprisingly varied in its properties.
The new maps hint at the asteroid’s history. Its rocky regions could be vestiges of an ancient mantle — similar in composition to the rocky outermost layer of Earth, Mars, and the asteroid Vesta — or the imprint of past impacts by space rocks. Finally, craters that contain metallic material support the idea proposed by previous studies that the asteroid may have experienced early eruptions of metallic lava as its ancient core cooled.
“Psyche’s surface is very heterogeneous,” says lead author Saverio Cambioni, the Crosby Distinguished Postdoctoral Fellow in MIT’s Department of Earth, Atmospheric and Planetary Sciences (EAPS). “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.”
Cambioni’s co-authors are Katherine de Kleer, assistant professor of planetary science and astronomy at Caltech, and Michael Shepard, professor of environmental, geographical, and geological sciences at Bloomsburg University.
Telescope Power
The surface of Psyche has been a focus of numerous previous mapping efforts. Researchers have observed the asteroid using various telescopes to measure light emitted from the asteroid at infrared wavelengths, which carry information about Psyche’s surface composition. However, these studies could not spatially resolve variations in composition over the surface.
Cambioni and his colleagues instead were able to see Psyche in finer detail, at a resolution of about 20 miles per pixel, using the combined power of the 66 radio antennas of the Atacama Large Millimeter/submillimeter Array (
On the left, this map shows surface properties on Psyche, from sandy areas (purple/low) to rocky areas (yellow/high). The map on the right shows metal abundances on Psyche, from low (purple) to high (yellow).
To catch a match
In the new study, Cambioni ran simulations of Psyche to see which surface properties might best match and explain the measured thermal emissions. In each of hundreds of simulated scenarios, he set the asteroid’s surface with different combinations of materials, such as areas of different metal abundances. He modeled the asteroid’s rotation and measured how simulated materials on the asteroid would give off thermal emissions. Cambioni then looked for the simulated emissions that best matched the actual emissions measured by ALMA. That scenario, he reasoned, would reveal the likeliest map of the asteroid’s surface materials.
“We ran these simulations area by area so we could catch differences in surface properties,” Cambioni says.
The study produced detailed maps of Psyche’s surface properties, showing that the asteroid’s façade is likely covered in a large diversity of materials. The researchers confirmed that, overall, Psyche’s surface is rich in metals, but the abundance of metals and silicates varies across its surface. This may be a further hint that, early in its formation, the asteroid may have had a silicate-rich mantle that has since disappeared.
They also found that, as the asteroid rotates, the material at the bottom of a large depression — likely a crater — changes temperature much faster than material along the rim. This suggests that the crater bottom is covered in “ponds” of fine-grained material, like sand on Earth, which heats up quickly, whereas the crater rims are composed of rockier, slower-to-warm materials.
“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 says. “But Psyche is a large body, so if fine-grained materials accumulated on the bottom of the depression, this is interesting and somewhat mysterious.”
“These data show that Psyche’s surface is heterogeneous, with possible remarkable variations in composition,” says Simone Marchi, staff scientist at the Southwest Research Institute and a co-investigator on NASA’s Psyche mission, who was not involved in the current study. “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 heterogeneties is something that the Psyche Science Team is eager to study more.”
Reference: “The Heterogeneous Surface of Asteroid (16) Psyche” by Saverio Cambioni, Katherine de Kleer and Michael Shepard, 19 May 2022, Journal of Geophysical Research: Planets. DOI: 10.1029/2021JE007091
This research was supported by the EAPS Crosby Distinguished Postodoctoral Fellowship, and in part by the Heising-Simons Foundation.
