In 2022, if all goes well, NASA will launch Psyche, a space probe intended to visit the asteroid of the same name (16 Psyche is its formal designation). It’s a particularly exciting mission given Psyche’s unique nature and highly unusual composition.

The asteroid belt is composed of three types of asteroid: C-type (carbonaceous, ~75 percent of all asteroids), S-type (silicate-rich, ~17 percent of asteroids) and M-type (metal-rich), which are roughly 10 percent of the total population. The numbers, in this case, don’t add up to 100 percent because we aren’t sure of the exact ratios. 16 Psyche is an M-type asteroid made of iron-nickel. What makes it unusual is that it’s believed to be the now-exposed core of a protoplanet. It’s also estimated to be worth $10,000 quadrillion dollars, if anybody has a towing hitch handy.

16 Psyche isn’t large — its radius is estimated at 112 km, and it isn’t round. Our current best estimate of its composition indicates that it’s 90 percent iron. Its parent body, assuming that it had one, is assumed to have been approximately 500km in diameter, or roughly half the size of Ceres. If Psyche is a core remnant it’s possible that others remain as well, but the asteroid isn’t part of any known family. One theory for its formation is that it was struck a number of times, but never with enough force to shatter it. The remaining fragment represents the iron core of a protoplanet, possibly covered by a thin layer of silicates or remnant components of the original mantle.

Psyche’s high iron content means it punches above its weight class as far as mass. While it’s listed as the 11th most-massive asteroid on Wikipedia, it has the 35th largest diameter. Psyche is considered the most massive M-type asteroid, with a mass of 2.23±0.36×1019 kg.

Psyche represents two fascinating opportunities. First, it’s the only known ‘iron world’ in the solar system. Second, it’s likely the closest we will ever come to examining the core of an actual planet. We could theoretically learn a great deal about the earliest protoplanets — now-vanished objects believed to have formed the inner planets and contributed to the mass of the outer billions of years ago.

Currently, the Psyche spacecraft is under preliminary design review. NASA is reviewing the plans for the mission ahead of a decision next month to start construction of the vehicle or not.

“The state of the art is profound ignorance about what we expect to find,” Jim Bell, the deputy principal investigator of the Psyche mission, told Smithsonian.com. “We are trying to prepare for any eventuality, no matter what it’s like. Our instruments will make interesting measurements, observations and discoveries that will allow us to put the history of that object back together.”

Feature Image credit: SSL/ASU/P. Rubin/NASA/JPL-Caltech

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