In 2022 NASA will launch a spacecraft to the asteroid Psyche (16 Psyche), one of the largest in the asteroid belt and the only known asteroid made almost entirely of metals such as iron and nickel.
Now scientists have re-examined Psyche with the Hubble Space Telescope and made the first ultraviolet observations of this asteroid since the 1980s. Hubble has given new insights into the surface and composition of psyche as well as into possible activities on the surface of psyche.
"For the first time we were able to determine what we believe to be iron oxide ultraviolet absorption bands on an asteroid," said the planetary scientist Dr. Tracy Becker of the Southwest Research Institute, lead author of a new paper describing the observations. "This is an indication that the asteroid is oxidizing, which could be due to the solar wind hitting the surface."
Scientists have long speculated that this metallic asteroid could be the leftover surviving core of a protoplanet, possibly with a violent collision with a planetesimal pulled off Psyche's outer, rocky layers, leaving only the dense, metallic interior. This theory has been supported by estimates of Psyche's bulk density, spectra, and radar surface properties, all of which show that it is an object no different from any other in the asteroid belt. In addition, this composition of 16 psyche is strikingly similar to that of the metal core of the earth.
The asteroid Psyche is one of the larger asteroids. Photo credit: Lindy T. Elkins-Tanton
"We have seen meteorites that are mostly made of metal, but Psyche could be unique in that it is an asteroid made entirely of iron and nickel," Becker said in a press release. “The earth has a metal core, a mantle and a crust. It is possible that a forming psyche protoplanet was hit by another object in our solar system and lost its mantle and crust. "
Becker and her team used Hubble to make high-resolution UV observations of the psyche, recorded in 2017 with the observatory's Space Telescope Imaging Spectrograph (STIS). They observed the asteroid at two specific points in its rotation to fully view both sides of the psyche at ultraviolet (UV) wavelengths.
Illustration 1. Orientation of the psyche at the time of the two HST observations. With kind permission of Becker et al.
They observed some small spectral differences between the sides, possibly suggesting an unusual feature in the northern hemisphere, but overall the spectra observed indicated that iron is the primary surface feature.
"We didn't find any significant spectral variations in the rotation, although the equatorial region of the asteroid may have a higher total reflectivity than the northern hemisphere," the team wrote in their paper. The psyche seemed to be increasingly reflective even at lower UV wavelengths.
"This is something we have to study further," said Becker. “This could indicate that it was exposed in space for so long. This type of UV brightening is often attributed to weathering in space. "
The team also compared the spectrum of the psyche with meteorite samples from a particular database, but found no strong matches.
The observations were made in preparation for the Psyche mission, which will travel to the asteroid to understand the origins of the planetary nuclei. The mission is to start in 2022 and arrive in Psyche in 2026. Because the asteroid Psyche is so far from Earth – approximately 280,000,000 km – we have no clear understanding or images of this object. Metal asteroids are relatively rare in the solar system, and scientists believe that Psyche could offer a unique opportunity to see into a planet.
"What makes Psyche and the other asteroids so interesting is that they are seen as the building blocks of the solar system," said Becker. “It's fascinating to understand what really makes a planet and possibly to see the inside of a planet. Once we get to Psyche, we will really understand if this is the case, even if it is not what we expect. Whenever there is a surprise, it is always exciting. "
The study was published in the Planetary Science Journal and presented last week at the virtual meeting of the Planetary Science Division of the American Astronomical Society
Lead Caption: Artist's impression of the massive asteroid 16 Psyche. Photo credit: Maxar / ASU / P. Rubin / NASA / JPL-Caltech.