Astronomers reveal the most detailed map of asteroid Psyche yet

Extend / Astronomers at MIT and elsewhere have mapped the composition of asteroid Psyche, revealing a surface of metal, sand and rock.

NASA

Astronomers have produced the most detailed map to date of the surface of 16-Psyche, an asteroid that scientists believe may hold clues to how planets formed in our Solar System. According to a paper published in the Journal of Geophysical Research, 16-Psyche has a highly varied surface of metal, sand and rock that suggests its history may include metallic eruptions as well as being hit by other celestial objects. The asteroid is the focus of NASA’s Psyche mission, which will launch later this year.

As we previously reported, 16 Psyche is an M-type asteroid (meaning it has a high metallic content) orbiting the Sun in the main asteroid belt, with an unusual potato shape. The long-held preferred hypothesis is that Psyche is the exposed metallic core of a protoplanet (planetesimal) from the earliest days of our Solar System, with the crust and mantle torn away by a collision (or multiple collisions) with other objects. In recent years, scientists have concluded that mass and density estimates are not consistent with an all-metallic remnant core. Rather, it is more likely to be a complex mixture of metals and silicates.

Alternatively, the asteroid may have been a parent body for a particular class of stony iron meteorites, one that broke up and reassembled into a mixture of metal and silicate. Or maybe it’s an object like 1 Ceres, a dwarf planet in the asteroid belt between the orbits of Mars and Jupiter — except that 16 Psyche may have experienced a period of iron volcanism as it cooled, leaving highly enriched metals in these volcanic centers.

Scientists have long suspected that metallic cores lurk deep within terrestrial planets like Earth. But these cores are buried far below rocky mantles and crusts for researchers to discover. As the only metallic core-like body discovered, Psyche offers the perfect opportunity to shed light on how the rocky planets in our Solar System (Earth, Mercury, Venus and Mars) might have formed. NASA approved the Psyche mission in 2017, with the intention of sending a spacecraft to orbit the asteroid and collect crucial data about its characteristics.

On the left, the map shows the surface properties in Psyche, from sandy areas (purple/low) to rocky areas (yellow/high). The map on the right shows the abundance of metals in Psyche, from low (purple) to high (yellow).

Previous mapping efforts relied on measuring the infrared light reflected off the asteroid’s surface with multiple telescopes around the world. Last year, astronomers produced a much higher resolution map of the surface of Psyche, based on 2019 observational data collected by all 66 radio antennas on the Atacama Large Millimeter/submillimeter Array (ALMA) in Chile.

By combining all of these signals into a single synthetic signal, the team achieved the equivalent resolution of a telescope with a diameter of 16 kilometers (10 miles) – about 20 miles per pixel. This view allowed them to resolve many compositional variations on the asteroid’s surface. They used this to create a map of the asteroid’s surface thermal emissions and a high-resolution 3D model of Psyche.

This latest map is based on hundreds of computer-simulated scenarios, each showing a different combination of surface material composition, taking into account the asteroid’s rotation. The team then compared these simulations with actual thermal emissions in the ALMA data to determine the most likely map of 16-Psyche’s surface.

The results: the asteroid is rich in metals, but the distribution varies across its surface. A similar and varied distribution of silicates suggests that 16-Psyche may have had a silicate-rich mantle. In addition, material at the bottom of craters changes temperature more rapidly than along the rim as the asteroid rotates. The authors suggest that these craters may have deposits (“ponds”) of fine sand. This is somewhat surprising given 16-Psyche’s mass and stronger gravity, compared to smaller asteroids that have fine-grained materials.

“These data show that the surface of Psyche is heterogeneous, with possible notable variations in composition,” said Simone Marchi of the Southwest Research Institute, a co-investigator on the Psyche mission who was not involved in the current study. “One of the main goals of the Psyche mission is to study the asteroid’s surface composition using its gamma-ray and neutron spectrometer and a color imager. more.”

DOI: Journal of Geophysical Research, 2022. 10.1029/2021JE007091/a> (About DOIs).

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