The asteroid Psyche's diverse surface points to a dynamic past that may have included metallic outbursts, asteroid-shaking collisions, and a missing rocky mantle.
A probe the size of a tennis court will be sent by NASA to the asteroid belt later this year. The asteroid belt is an area between Mars' and Jupiter's orbits where objects from the early solar system circle the sun. The spacecraft will focus on Psyche, a large, metal-rich asteroid that is supposed to represent the ancient core of an early planet, after it has entered the asteroid belt. The probe, which is named after the asteroid it is orbiting, will then spend nearly two years orbiting and studying the surface of Psyche to look for hints about the origins of early planetary bodies.
Planetary scientists from MIT and other institutions have now given a preview of what the Psyche spacecraft could encounter when it reaches its target ahead of the mission, which is headed by principle investigator Lindy Elkins-Tanton '87, SM '87, PhD '02.
The planetary research team, based on observations made by a large number of ground telescopes in northern Chile, gives the most thorough mapping of the asteroid's surface characteristics to date in an article that will be released on June 15, 2022 in the Journal of Geophysical Research: Planets.
A big depression that appears to have a varied surface texture between its inside and its border may indicate a crater filled with finer sand and surrounded with rockier materials, according to the maps that show broad metal-rich patches spreading across the asteroid's surface.
The asteroid's past is suggested by the new maps. Its rocky portions may represent remnants of an old mantle, akin to the rocky outermost layer of Mars, Vesta, and Earth in composition, or they may be the result of previous strikes by space objects. Last but not least, metallic-rich craters lend credence to the theory advanced in earlier research that the asteroid may have seen early discharges of metallic lava when its old core cooled.
Lead author Saverio Cambioni, the Crosby Distinguished Postdoctoral Fellow in MIT's Department of Earth, Atmospheric and Planetary Sciences, claims that "Psyche's surface is extraordinarily diverse" (EAPS). These maps demonstrate that metal-rich asteroids are fascinating, mysterious planets because they have an evolving surface. It's yet more cause to anticipate the Psyche mission's trip to the asteroid.
Co-authors with Cambioni are Michael Shepard, a professor of environmental, geographical, and geological sciences at Bloomsburg University, and Katherine de Kleer, an assistant professor of planetary science and astronomy at Caltech.
Telescope Power
Numerous earlier mapping projects have focused on the surface of Psyche. Infrared light from the asteroid, which contains details on the surface composition, has been measured by researchers using a variety of telescopes to view the object. These analyses, however, were unable to spatially clarify surface compositional changes. Instead, using the combined strength of the 66 radio antennas of the Atacama Large Millimeter/submillimeter Array (ALMA) in northern Chile, Cambioni and his colleagues were able to view Psyche in more detail, at a resolution of around 20 miles per pixel. Within a range that is sensitive to temperature and certain electrical characteristics of surface materials, each ALMA antenna monitors light emitted from an object at millimeter wavelengths.
De Kleer claims that the signals from the ALMA antennas may be merged to create a synthetic signal that is comparable to a telescope with a 16 km (10 mi) diameter. "The resolution increases with the size of the telescope."
On June 19, 2019, Psyche orbited and rotated within the asteroid belt, and ALMA focused its complete array on it. De Kleer gathered information throughout this time and used it to create a map of thermal emissions over the surface of the asteroid, which the team then published in a research in 2021. The most current high-resolution 3D shape model of Psyche, which was also released in 2021, was created by Shepard using the same data.
finding a match
Cambioni performed simulations of Psyche in the current study to see which surface characteristics may most closely match and explain the observed thermal emissions. He configured the surface of the asteroid with various combinations of components, such as regions with various metal abundances, in each of hundreds of simulated scenarios. He measured the heat emissions produced by the simulated materials on the asteroid and modelled the asteroid's rotation. Then, Cambioni sought for the model emissions that most closely matched the real emissions detected by ALMA. He reasoned that scenario would provide the most accurate picture of the asteroid's surface composition.
To detect variations in surface qualities, Cambioni explains, "we conducted these simulations area by area."
The research created in-depth maps of Psyche's surface characteristics, demonstrating that the asteroid's surface is probably made up of a wide variety of components. Overall, the researchers found that Psyche's surface is rich in metals, albeit there are regional variations in the distribution of metals and silicates. This might be even more indication that the asteroid formerly had a silicate-rich mantle that has since vanished.
They also discovered that material near the bottom of a significant depression, which is probably a crater, changes temperature considerably more quickly than material around the rim when the asteroid spins.
This implies that the crater edges are made of rockier, slower-warming elements, and the crater bottom is covered with "ponds" of fine-grained material, similar to sand on Earth.
Small asteroids, whose gravity is low enough for impacts to disturb the surface and cause finer materials to pool, have ponds of fine-grained minerals, according to Cambioni. However, given the size of Psyche, it is intriguing and a little strange whether fine-grained minerals gathered there.
This implies that the crater edges are made of rockier, slower-warming elements, and the crater bottom is covered with "ponds" of fine-grained material, similar to sand on Earth.
Small asteroids, whose gravity is low enough for impacts to disturb the surface and cause finer materials to pool, have ponds of fine-grained minerals, according to Cambioni. However, given the size of Psyche, it is intriguing and a little strange whether fine-grained minerals gathered there.
According to Simone Marchi, a staff scientist at the Southwest Research Institute and a co-investigator on NASA's Psyche project, who was not involved in the present study, "These findings reveal that Psyche's surface is diverse, with possibly dramatic fluctuations in composition." "Using its gamma rays and neutron spectrometer, together with a color imager, the Psyche mission's principal objective is to examine the composition of the asteroid surface. The Psyche Science Team is thus interested to learn more about the potential existence of compositional heterogeneities.
