Astronomers at the Massachusetts Institute of Technology and elsewhere have mapped the composition of the asteroid Psyche, revealing a surface of metal, sand and rock. Credit: Screenshot courtesy of NASA
The diverse surface of the asteroid Psyche suggests a dynamic history, which may include metal eruptions, shaking asteroid impacts and a lost rock mantle.
Later this year, NASA will launch a tennis court-sized probe to the asteroid belt, a region between the orbits of Mars and Jupiter, where remnants of the early solar system orbit the sun. Once in the asteroid belt, the spacecraft will head to Psyche, a large, metal-rich asteroid believed to be the ancient core of an early planet. The probe, named after its asteroid target, will then spend nearly two years in orbit, analyzing Psyche’s surface for clues as to how early planetary bodies evolved.
Prior to the mission led by Principal Investigator Lindy Elkins-Tanton ’87, SM ’87, PhD ’02, planetary scientists at the Massachusetts Institute of Technology and elsewhere have now provided a brief overview of what the Psyche spacecraft can see when it reaches your destination.
In an article published on June 15, 2022 in the Journal of Geophysical Research: Planets, the planetary science team presents the most detailed maps of the asteroid’s surface properties to date, based on observations made by a large set of ground-based telescopes in northern Chile . The maps reveal vast metal-rich regions that extend along the asteroid’s surface, along with a major depression that appears to have a different surface texture between the interior and its edge; this difference may reflect a crater filled with finer sand and surrounded by more rocky materials.
This illustration, updated in April 2022, depicts NASA’s Psyche spacecraft. Scheduled to launch in August 2022, the Psyche mission will explore a metal-rich asteroid of the same name located 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 study its composition. Credit: NASA / JPL-Caltech / ASU
In general, the surface of Psyche was found to be surprisingly diverse in its properties.
The new maps hint at the history of the asteroid. Its rocky areas could be remnants of an ancient mantle – similar in composition to the rocky outermost layer of Earth, Mars and the asteroid Vesta – or an imprint of past impacts from space rocks. Finally, craters containing metallic material support the idea suggested by previous studies that the asteroid may have had early eruptions of metal lava while its ancient core was cooling.
“The surface of the Psyche is very heterogeneous,” said lead author Saverio Cambioni, a prominent postdoctoral fellow at Crosby’s in the Department of Earth, Atmospheric and Planetary Sciences at the Massachusetts Institute of Technology (EAPS). “This is an evolved surface, and these maps confirm that metal-rich asteroids are interesting, mysterious worlds. This is another reason to look forward to Psyche’s mission to the asteroid.
Cambion’s co-authors are Catherine 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 at the center of many previous mapping efforts. Researchers have observed the asteroid with the help of various telescopes to measure the light emitted by the asteroid at infrared wavelengths, which carry information about the surface composition of Psyche. However, these studies cannot spatially resolve variations in surface composition.
Instead, Cambioni and his colleagues were able to see the Psyche in finer detail, with a resolution of about 20 miles per pixel, using the combined power of the 66 Atacama Large Millimeter / Submilimeter Array (ALMA) radio antennas in northern Chile. Each ALMA antenna measures the light emitted by an object with millimeter wavelengths in a range that is sensitive to the temperature and certain electrical properties of the surface materials.
“ALMA antenna signals can be combined into a synthetic signal that is equivalent to a 16-kilometer (10-mile) telescope,” says de Kleer. “The bigger the telescope, the higher the resolution.”
On June 19, 2019, ALMA focused its entire array on Psyche as it orbited and rotated in the asteroid belt. De Kleer collected data during this period and converted it into a map of heat emissions on the asteroid’s surface, which the team reported in a study from 2021. The same data was used by Shepard to produce the latest 3D model of Psyche with high resolution , also published in 2021
On the left, this map shows the properties of the Psyche surface, from sandy areas (purple / low) to rocky areas (yellow / high). The map on the right shows the abundance of Psyche’s metals, from low (purple) to high (yellow).
To catch a match
In the new study, Cambioni conducted simulations of Psyche to see which surface properties could best match and explain the measured heat emissions. In each of the hundreds of simulated scenarios, he sets the surface of the asteroid with different combinations of materials, such as areas with different metal abundance. It simulates the rotation of the asteroid and measures how the simulated materials of the asteroid will emit heat emissions. Cambioni then looked for the simulated emissions that best matched the actual emissions measured by ALMA. This scenario, he reasoned, would reveal the most likely map of the asteroid’s surface materials.
“We did these simulations area by area so we could capture differences in surface properties,” says Cambioni.
The study created detailed maps of Psyche’s surface properties, showing that the asteroid’s facade was probably covered with a wide variety of materials. Researchers have confirmed that the surface of Psyche is generally rich in metals, but the abundance of metals and silicates varies throughout its surface. This may be an additional hint that the asteroid may have had a silicate-rich mantle at the beginning of its formation, which has since disappeared.
They also found that as the asteroid rotated, the material at the bottom of the Great Depression – probably a crater – changed temperature much faster than the material along the edge. This suggests that the bottom of the crater is covered with “lakes” of fine-grained material, such as sand on Earth, which heats up quickly, while the edges of the crater are composed of rocky, slower-warming materials.
“Fine-grained lakes have been observed on small asteroids, whose gravity is low enough for shocks to shake the surface and cause finer materials to collect,” says Cambioni. “But the psyche is a big body, so if fine-grained material accumulates at the bottom of the depression, it’s interesting and somewhat mysterious.”
“These data show that the surface of Psyche is heterogeneous, with possible remarkable variations in composition,” said Simone Marchi, a scientist at the Southwestern Research Institute and a co-researcher at NASA’s Psyche mission who was not involved in the study. “One of the main goals of the Psyche mission is to study the composition of the asteroid’s surface using gamma rays and the neutron spectrometer and color image. So the possible presence of compositional heterogeneities is something the Psyche Science team wants to explore more. “
Reference: “The Heterogeneous Surface of the Asteroid (16) Psyche” by Saverio Cambioni, Catherine de Kleer and Michael Shepard, May 19, 2022, Journal of Geophysical Research: Planets.DOI: 10.1029 / 2021JE007091
This study was supported by the EAPS Crosby Distinguished Postodoctoral Fellowship and in part by the Heising-Simons Foundation.
Add Comment