New University of Arizona research finds that the target asteroid to NASAPsyche mission may not be as metallic or dense as previously predicted.
The widely studied metallic asteroid known as 16 Psyche was long thought to be the exposed iron core on a small planet that did not form in the early days of the solar system. But new research from the University of Arizona suggests that the asteroid may not be as metallic or dense as was once thought, and suggests a very different origin story.
Scientists are interested in 16 psyche, because if its presumed origin is true, it would provide an 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 undergraduate student David Cantillo is the lead author of a new paper published in Planetary Science Journal which suggests that 16 Psyche is 82.5% metal, 7% low iron pyroxene and 10.5% carbonaceous chondrite, which was probably supplied by shocks from other asteroids. Cantillo and his collaborators estimate that the bulk density of 16 Psyches – also known as porosity, which refers to how much empty space is found in its body – is around 35%.
These estimates differ from previous analyzes of the composition of 16 Psyches, which led researchers to estimate that it could contain as much as 95% metal and be much denser.
“That drop in metal content and density is interesting because it shows that 16 Psyche is more modified than previously thought,” Cantillo said.
Instead of being an intact exposed core of an early planet, it may actually be closer to a rubble resembling another thoroughly studied asteroid – Bennu. UArizona leads the NASA Science Mission Team OSIRIS-REx mission that retrieved a sample from Bennus’ surface that is now returning to Earth.
“Psyche as rubble would be very unexpected, but our data continue to show estimates of low density despite its high metal content,” Cantillo said.
Asteroid 16 Psyche is about the size of Massachusetts, and researchers estimate that it contains approx. 1% of all asteroid band material. First discovered by an Italian astronomer in 1852, it was the 16th asteroid ever discovered.
“Having a lower metal content than once thought means the asteroid could have been exposed to collisions with asteroids containing the more common carbonaceous chondrites that deposited a surface layer that we observe,” Cantillo said. This was also observed on the asteroid Vesta by the NASA Dawn spacecraft.
Asteroid 16 Psyche has been estimated to be worth $ 10,000 quadrillion (that’s $ 10,000 followed by another 15 zeros), but the new findings could hover a bit the iron-rich asteroid.
“This is the first paper that places some specific restrictions on its surface content. Previous estimates were a good start, but this improves these numbers a little more, ”said Cantillo.
The other well-studied asteroid, Bennu, contains a lot of carbonaceous chondrite material and has a porosity of over 50%, which is a classic property of a rubble.
Such high porosity is common for objects with relatively small and low masses such as Bennu – which are only as large as the Empire State Building – because a weak gravitational field prevents the object’s rocks and stones from being packed too tightly. But for an object the size of 16 psyche to be so porous is unexpected.
“The ability to study an exposed core 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.”
Previous estimates of the composition of 16 Psyches were made by analyzing the sunlight reflected from the surface. The light pattern matched it with other metal objects. Cantillo and his collaborators instead recreated 16 Psyche’s regolith – or loose rocky surface material – by mixing different materials in a laboratory and analyzing light patterns until they matched telescopic observations of the asteroid. There are few laboratories 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 in high school.
“I’ve always been interested in space,” said Cantillo, who is also president of the Arizona Astronomy Club. “I knew that studying astronomy would be heavy on computers and observation, but I like to do more practical work, so I would somehow connect my studies to geology. I take geology and teaching planetary science and math. ”
“David’s paper is an example of the groundbreaking research work being done by our students,” said co-author Vishnu Reddy, an associate professor of planetary science who heads the laboratory where Cantillo works. “It’s also a great example of a collaborative effort between students, graduate students, postdoctoral fellows, and staff in my laboratory.”
The scientists 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 terrestrial telescopes and spacecraft missions to other asteroids to help determine the amount of water present.
Reference: “Constraining the Regolith Composition of Asteroid (16) Psyche via Laboratory Visible Near-infrared Spectroscopy” by David C. Cantillo, Vishnu Reddy, Benjamin NL Sharkey, Neil A. Pearson, Juan A. Sanchez, Matthew RM Izawa, Theodore Kareta , Tanner S. Campbell and Om Chabra, 12 May 2021, Planetary Science Journal.
DOI: 10.3847 / PSJ / abf63b
Funding: NASA Near-Earth Object Observations Program