New Maps of Asteroid Psyche Reveal an Ancient World of Metal and Rock

Later this year, NASA is set to launch a tennis-court-sized probe into the asteroid belt, a region between the orbits of Mars and Jupiter where remnants of the early solar system orbit of the sun. Once inside the asteroid belt, the spacecraft will zero in on Psyche, a large, metal-rich asteroid believed to be the ancient core of an early planet. The probe, named after its target asteroid, will then spend nearly two years in orbit and scan Psyche’s surface for clues to the evolution of early planetary bodies.

Ahead of the mission, which is led by Principal Investigator Lindy Elkins-Tanton ’87, SM ’87, PhD ’02, planetary scientists at MIT and elsewhere have now provided a glimpse of what the Psyche spacecraft might see when he will reach his destination. .

In a paper published today in the Journal of Geophysical Research: Planets, the team presents the most detailed maps of the asteroid’s surface properties to date, based on observations taken by a wide range of ground-based telescopes. in northern Chile. The maps reveal large metal-rich regions sweeping across the asteroid’s surface, as well as a large depression that appears to have a different surface texture between the interior and its edge; this difference could reflect a crater filled with finer sand and lined with rockier material.

Overall, the surface of Psyche turned out to be surprisingly varied in its properties.

The new maps allude to the asteroid’s history. Its rocky regions could be remnants of an ancient mantle – similar in composition to the outermost rock layer of Earth, Mars and the asteroid Vesta – or the imprint of past impacts by space rocks. Finally, the craters containing metallic material support the idea proposed by previous studies that the asteroid may have experienced early eruptions of metallic lava as its former core cooled.

“The surface of Psyche is very heterogeneous,” says lead author Saverio Cambioni, 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 and enigmatic worlds. This is another reason to look forward to the Psyche mission heading to the asteroid.

Cambioni’s co-authors are Katherine de Kleer, assistant professor of planetary sciences and astronomy at Caltech, and Michael Shepard, professor of environmental, geographic and geological sciences at Bloomsburg University.

telescope power

The surface of Psyche has been the subject of many previous mapping efforts. The researchers observed the asteroid using various telescopes to measure the light emitted by the asteroid at infrared wavelengths, which contain information about the composition of Psyche’s surface. However, these studies could not spatially resolve compositional variations on the surface.

Cambioni and his colleagues were instead able to see Psyche in greater detail, at a resolution of around 20 miles per pixel, using the combined power of the 66 radio antennas of the Atacama Large Millimeter/submillimeter Array (ALMA) in northern Chile. . Each ALMA antenna measures light emitted by an object at millimeter wavelengths, in a range sensitive to temperature and certain electrical properties of surface materials.

“The signals from the ALMA antennas can be combined into a synthetic signal equivalent to a telescope with a diameter of 16 kilometers (10 miles),” de Kleer explains. “The larger the telescope, the higher the resolution.”

On June 19, 2019, ALMA focused its entire network on Psyche as it tossed and turned in 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 recent high-resolution 3D shape model of Psyche, also published in 2021.

To catch a match

In the new study, Cambioni ran Psyche simulations to see which surface properties might best match and explain the measured thermal emissions. In each of the hundreds of simulated scenarios, he defined the asteroid’s surface with different combinations of materials, such as areas of different metal abundances. He modeled the rotation of the asteroid and measured how simulated materials on the asteroid would give off thermal emissions. Cambioni then searched 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 ran these simulations area by area so that we could detect differences in surface properties,” Cambioni explains.

The study produced detailed maps of Psyche’s surface properties, showing that the asteroid’s facade is likely covered in a wide variety of materials. The researchers confirmed that, overall, the surface of Psyche is rich in metals, but the abundance of metals and silicates varies across its surface. This may be a further clue 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 the material along the edge. This suggests that the crater floor is lined with “pools” of fine-grained material, like sand on Earth, which heats up quickly, while the crater rims are composed of rockier, slower-heating material.

“Pools of fine-grained material have been observed on small asteroids, whose gravity is low enough that impacts shake the surface and cause finer material to accumulate,” Cambioni explains. “But Psyche is a large 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 Southwest Research Institute and co-investigator of NASA’s Psyche mission, who was not involved in the study. current study. “One of the main objectives of the Psyche mission is to study the composition of the asteroid’s surface using its gamma-ray and neutron spectrometer and a color imager. Thus, the possible presence of compositional heterogeneities is something the Psyche Science team is eager to investigate further.

This research was supported by the EAPS Crosby Distinguished Postdoctoral Fellowship and in part by the Heising-Simons Foundation.

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