The widely studied metallic asteroid known as 16 Psyche has long been considered the exposed iron core of a small planet that did not form during the early days of the solar system. But new research from the University of Arizona suggests the asteroid may not be as metallic or dense as it once was thought, and hints at a much different origin story.
Scientists are interested in 16 Psyche because if its presumed origins are true, it would provide the opportunity to closely study an exposed planetary core. NASA is expected to launch its Psyche mission in 2022 and arrive on the asteroid in 2026.
Arizona undergraduate student David Cantillo is the lead author of a new article published in The Journal of Planetary Sciences which features 16 Psyche is 82.5% metal, 7% low iron pyroxene and 10.5% carbonaceous chondrite which was likely delivered by impacts from other asteroids. Cantillo and colleagues estimate that the bulk density of 16 Psyche – also known as porosity, which refers to the amount of empty space in its body – is around 35%.
These estimates differ from previous analyzes of the composition of 16 Psyche which led researchers to estimate that it could contain up to 95% metal and be much denser.
“This drop in metal content and bulk density is interesting because it shows that 16 Psyche is more modified than previously thought,” Cantillo said.
Rather than being an intact exposed core of a primitive planet, it might actually be closer to a rubble heap, similar to another carefully studied asteroid – Bennu. UArizona is leading NASA’s OSIRIS-REx science mission team, which recovered a surface sample from Bennu who is now returning to Earth.
“The psyche as a pile of rubble would be very unexpected, but our data continues to show estimates of low density despite its high metal content,” Cantillo said.
Asteroid 16 Psyche is about the size of Massachusetts, and scientists estimate it contains about 1% of all material in the asteroid belt. First spotted by an Italian astronomer in 1852, it was the 16th asteroid ever to be discovered.
“Having a lower metal content than previously thought means the asteroid could have been exposed to collisions with asteroids containing the most common carbonaceous chondrites, which deposited a surface layer that we are observing,” Cantillo said. This has also been observed on the asteroid Vesta by NASA’s Dawn spacecraft.
Asteroid 16 Psyche has been estimated at $ 10,000 quadrillion (or $ 10,000 followed by 15 more zeros), but the new findings could slightly devalue the iron-rich asteroid.
“This is the first article to define specific constraints on its surface content. Earlier estimates were a good start, but it refines those numbers a bit further,” Cantillo said.
The other well-studied asteroid, Bennu, contains a lot of carbonaceous chondrite and has a porosity of more than 50%, a classic characteristic of a pile of rubble.
Such high porosity is common for relatively small, low-mass objects such as Bennu – which is only as large as the Empire State Building – because a weak gravitational field prevents rocks and boulders in the object from being too tight. But for an object the size of Psyche 16 to be so porous, it’s unexpected.
“The opportunity to study an exposed nucleus of a planetesimal is extremely rare, which is why they are sending the space mission there,” Cantillo said, “but our work shows that 16 Psyche is much more interesting than expected.”
Earlier estimates of the composition of 16 Psyche were made by analyzing sunlight reflected from its surface. The pattern of the light matched that of other metallic objects. Instead, Cantillo and his collaborators recreated 16 Psyche’s regolith – or loose rock surface material – by mixing different materials in a lab and analyzing the light patterns until they matched the asteroid’s telescope observations. There are only a few labs in the world that practice this technique, including the UArizona Lunar and Planetary Laboratory and the Johns Hopkins Applied Physics Laboratory in Maryland, where Cantillo worked while in high school.
“I’ve always been interested in space,” said Cantillo, who is also president of the UArizona Astronomy Club. “I knew astronomical studies would be heavy on computers and observation, but I like to do more hands-on work, so I wanted to relate my studies to geology in some way. specializes in geology and planetary sciences and mathematics. “
“David’s article is an example of the cutting-edge research work being done by our undergraduates,” said study co-author Vishnu Reddy, associate professor of planetary sciences who heads the lab in which Cantillo works. . “It’s also a great example of the collaborative effort among undergraduates, graduate students, postdoctoral fellows and staff in my lab. “
The researchers also believe that the carbonaceous material on the surface of 16 Psyche is rich in water. So they will then work to merge data from ground telescopes and space missions to other asteroids to help determine how much water is present.