The varied surface of the asteroid Psyche suggests a dynamic story, which could include metal explosions, trembling asteroids and a lost rock mantle. Later this year, NASA plans to launch a probe the size of a tennis court into the asteroid belt, an area between the orbits of Mars and Jupiter where remnants of the early solar system revolve around the sun. Once in the asteroid belt, the spacecraft will zero in on Psyche, a large, mineral-rich asteroid believed to be the ancient nucleus of an early planet. The probe, named after its asteroid target, will then spend nearly two years roaming and analyzing the surface of the Soul for clues as to how the first planetary bodies evolved. Prior to the mission, led by lead researcher Lindy Elkins-Tanton ’87, SM ’87, PhD ’02, planetary scientists at MIT and elsewhere now gave a sneak peek at what the Psyche spacecraft could see when it arrived. In a paper published 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 number of ground-based telescopes in the north. Chile. The maps reveal huge areas rich in minerals that sweep the asteroid’s surface, along with a large cavity that appears to have a different surface texture between the inside and the rim. this difference could reflect a crater filled with finer sand and fenced with more rocky material. This image, updated in April 2022, depicts NASA’s Psyche spacecraft. The Psyche mission is set to launch in August 2022, exploring 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 will be in orbit around the asteroid – also seen in this image – for almost two years to investigate its composition. Credit: NASA / JPL-Caltech / ASU Overall, the surface of the Psyche was found to vary dramatically in its properties. New maps hint at asteroid history. Its rocky regions could be remnants of an ancient mantle – similar in composition to the Earth’s rocky outermost layer, Mars and the asteroid Vesta – or the imprint of previous impacts from space rocks. Finally, craters containing metallic material support the idea suggested by previous studies that the asteroid may have experienced early metal lava eruptions as its ancient core cooled. “The surface of the Soul is very heterogeneous,” says lead author Saverio Cambioni, Crosby’s distinguished postdoctoral fellow at MIT’s Department of Earth, Atmosphere and Planetary Sciences (EAPS). “It’s an advanced 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 the asteroid.” Cambioni 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 Psyche surface has been the focus of many previous mapping efforts. The researchers observed the asteroid using various telescopes to measure the light emitted by the asteroid in infrared wavelengths, which convey information about the composition of the surface of the Soul. However, these studies were unable to resolve spatial variations in surface composition. Cambioni and his colleagues were able to see the Psyche in more 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 (ALMA) array in northern Chile. Each ALMA antenna measures the light emitted by an object in millimeter wavelengths, within an area that is sensitive to temperature and certain electrical properties of surface materials. “ALMA antenna signals can be combined into a synthetic signal equivalent to a 16-kilometer (10-mile) diameter telescope,” says de Kleer. “The larger the telescope, the higher the resolution.” On June 19, 2019, ALMA focused its entire array on the Soul as it orbited and rotated within the asteroid belt. De Kleer collected data during this period and converted it into a map of thermal emissions across the asteroid’s surface, which the team reported in a 2021 study. This same data was used by Shepard to produce the most Psyche’s latest high-resolution 3D model, also released in 2021. On the left, this map shows surface properties in Psyche, from sandy areas (purple / low) to rocky areas (yellow / high). The map on the right shows plenty of metals in Psyche, from low (purple) to high (yellow).
To catch a match
In the new study, Cambioni performed Psyche simulations to see which surface properties could best fit and explain the measured heat emissions. In each of the hundreds of simulated scenarios, he set the surface of the asteroid with different combinations of materials, such as areas with different abundances of metals. Model the asteroid’s rotation and measure how the simulated materials on the asteroid will emit heat. Cambioni then looked for the simulated emissions that best matched the actual emissions measured by ALMA. This scenario, he thought, would reveal the most likely map of the asteroid’s surface materials. “We performed these simulations by region so that we could detect differences in surface properties,” says Cambioni. The study produced detailed maps of Psyche’s surface properties, showing that the asteroid’s face is likely to be covered by a wide variety of materials. The researchers confirmed that, on the whole, Psyche’s surface is rich in minerals, but the abundance of metals and silicates varies throughout its surface. This may be a further indication 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 cavity – probably a crater – changes temperature much faster than the material along the rim. This suggests that the bottom of the crater is covered by “lakes” of fine-grained material, such as sand on Earth, which heats up quickly, while the crater’s lips are made up of rockier, slower to warmer materials. “Pools of fine-grained material have been observed in small asteroids, the gravity of which is low enough for the impact to shake the surface and cause finer material to accumulate,” says Cambioni. “But the Soul is a large body, so if fine-grained material accumulates at the bottom of the depression, that’s interesting and somewhat mysterious.” “These data show that the surface of the Psyche is heterogeneous, with potentially significant variations in composition,” said Simone Marchi, a scientist at the Southwest Research Institute and co-researcher on NASA’s Psyche mission, who did not participate in the current study. “One of the primary goals of the Psyche mission is to study the composition of the asteroid’s surface using gamma rays and neutron spectrometers and a color imaging. Thus, the possible presence of synthetic heterogeneities is something that the Psychic Science Team wants 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.
