Psyche May Not Be So Metal After All

An analysis of asteroid 16 Psyche’s gravitational effects on nearby bodies determines it must be less dense and less iron-rich than previously determined by its albedo.

Beth Johnson

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IMAGE: An artist’s rendering of Psyche, the largest of the metal-rich asteroids in the solar system. CREDIT: NASA/JPL-Caltech/ASU

A new mission is expected to launch this year to go and examine an interesting asteroid, 16 Psyche. That asteroid is thought to be made almost entirely of iron, suggesting that it could be the core of a larger body that either never fully formed or was somehow destroyed in a collision. There was even one article running around last year that estimated the value of Psyche’s metals as somewhere around $10 quintillion. No, seriously. Someone wrote that.

However, before all those wanna-be asteroid miners get their hopes up, new research published in JGR: Planets now suggests that Psyche is less metallic than previously thought. While light reflecting off the surface of the asteroid does suggest a darkness that belies a metallic composition, measurements of the mass and density do not match up with that hypothesis. In fact, per the press release: The way [Psyche’s] gravity tugs on neighboring bodies suggests that Psyche is far less dense than a giant hunk of iron should be. So if Psyche is indeed all metal, it would have to be highly porous — a bit like a giant ball of steel wool with nearly equal parts void space and solid metal.

Lead author Fiona Nichols-Fleming explains: What we wanted to do with this study was see whether it was possible for an iron body the size of Psyche to maintain that near-50% porosity. We found that it’s very unlikely.

For Psyche to have remained that highly porous, the internal temperature after formation would have had to be a rather cool 800 Kelvin. Otherwise, the iron would still be malleable, and the asteroid’s own gravity would have collapsed all the pore space and created a smaller, denser object. At 250 kilometers across, it couldn’t have cooled that quickly. Additionally, any impact that could have added that porosity back in by splintering the asteroid would also have heated it up above that same 800 Kelvin threshold, meaning that porous state wouldn’t last, either.

This new model suggests that Psyche may be hiding a rocky component that is making the…

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Beth Johnson

Planetary scientist, podcast host. Communication specialist for SETI Institute and Planetary Science Institute. Buy me a coffee: https://ko-fi.com/planetarypan