The much-studied metallic asteroid known as 16 Psyche was long thought to be the exposed iron core of a minor planet that did not form during the earliest days of the solar system. But new research led by the University of Arizona suggests the asteroid may not be as metallic or dense as once thought, pointing to a very different origin story.
Scientists are interested in 16 Psyche because if its supposed origin is true, it would provide the opportunity to study an exposed planetary core up close. NASA is scheduled to launch its Psyche mission in 2022 and arrive at the asteroid in 2026.
UArizona student David Cantillo is lead author of a new paper published in The Planetary Science Magazine representing 16 Psyche is 82.5% metal, 7% low-iron pyroxene, and 10.5% carbonaceous chondrite likely provided by impacts from other asteroids. Cantillo and his collaborators estimate that 16 Psyche’s bulk density — also known as porosity, which refers to how much empty space is found in his body — is about 35%.
These estimates differ from previous analyzes of 16 Psyche’s composition, which led researchers to estimate that it could contain as much as 95% metal and be much denser.
“That 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 from an early planet, it could actually be closer to a mess, similar to another thoroughly studied asteroid – Bennu. UArizona leads the science mission team for NASA’s OSIRIS-REx mission, which has retrieved a sample from Bennu’s surface that is now making its way back to Earth.
“Psyche as a mess would be very unexpected, but our data continues to show low density estimates despite the high metal content,” Cantillo said.
Asteroid 16 Psyche is about the size of Massachusetts and scientists estimate it contains about 1% of all the material of the asteroid belt. First noticed by an Italian astronomer in 1852, it was the 16th asteroid ever discovered.
“Having a lower metal content than once thought means the asteroid may have been exposed to collisions with asteroids that contain the more common carbonaceous chondrites, which deposit a surface layer we observe,” Cantillo said. This was also observed on asteroid Vesta by the NASA Dawn spacecraft.
Asteroid 16 Psyche is estimated to be worth $10,000 quadrillion (that’s $10,000, followed by 15 more zeros), but the new findings could devalue the iron-rich asteroid somewhat.
“This is the first paper to put some specific constraints on surface content. Previous estimates were a good start, but this refines those numbers a bit more,” Cantillo said.
The other well-studied asteroid, Bennu, contains a lot of carbonaceous chondrite material and has a porosity greater than 50%, which is a classic hallmark of a mess.
Such high porosity is common for relatively small, low-mass objects like Bennu — which is only as tall as the Empire State Building — because a weak gravitational field prevents the object’s rocks and boulders from being packed too tightly together. But that an object the size of 16 Psyche is so porous is unexpected.
“The opportunity to study an exposed nucleus of a planetesimal is extremely rare, which is why they are sending the spacecraft 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 the sunlight reflected from the surface. The light pattern matched that of other metal objects. Cantillo and his collaborators instead recreated 16 Psyche’s regolith — or loose rocky surface material — by mixing different materials in a lab and analyzing light patterns until they matched telescope observations of the asteroid. There are only a few labs in the world that use this technique, including the UArizona Lunar and Planetary Laboratory and the Johns Hopkins Applied Physics Laboratory in Maryland, where Cantillo worked in high school.
“I’ve always been interested in space,” said Cantillo, who is also president of the UArizona Astronomy Club. “I knew astronomy studies would be heavy on computers and observation, but I like to do more hands-on kind of work, so I wanted to somehow connect my studies with geology. I study geology and minor in planetary science and math. “
“David’s paper exemplifies the pioneering research work of our undergraduate studentssaid co-author Vishnu Reddy, an associate professor of planetary sciences who heads the lab in which Cantillo works. “It’s also a great example of the collaboration between 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 on merging data from ground-based telescopes and spacecraft missions with other asteroids to help determine the amount of water present.
David C. Cantillo et al, The Regolith Composition of Asteroid (16) Limiting Psyche via Laboratory Visible Near Infrared Spectroscopy, The Planetary Science Magazine (2021). DOI: 10.3847/PSJ/abf63b
University of Arizona
Quote: Asteroid 16 Psyche may not be what scientists expected (2021, June 9,), retrieved June 10, 2021 from https://phys.org/news/2021-06-asteroid-psyche-scientists.html
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