December 5, 2020
The asteroid 16 Psyche (named as such because it was the 16th to be discovered)...

The asteroid 16 Psyche (named as such because it was the 16th to be discovered) is believed to be the now-exposed core of a differentiated protoplanet that was smashed apart some billions of years ago. Its composition is generally estimated to be 90 percent metallic and 10 percent silicate rock. It’s thought to be much denser than a typical stony object of equivalent size, and it contains approximately 1 percent of the entire mass of the asteroid belt.

Assuming that the core is made of iron and nickel, the total value of the asteroid (if we ignore the impact on market prices) would be ~$10,000 quadrillion dollars. There’s a NASA mission to 16 Psyche expected to launch in 2022 and arrive in 2026, and the Hubble Space Telescope just spent some time surveying the core fragment. Psyche’s surface composition and what it’s made of have implications for the kinds of scientific tests and instruments that would be loaded on the probe we send to study the asteroid.

The researchers examined Psyche in the ultraviolet — it’s one of just a handful of asteroids to be examined this way — to see if telltale clues about how the light reflected off its surface could reveal details of the asteroid’s internal composition. The data they found generally supports a high iron composition for the object, but they noted that a relatively small amount of iron mixed into rocky materials like olivine can produce Psyche’s ultraviolet signature. This makes it “difficult to quantify the amount of iron that may present on the surface of Psyche.”

Psyche’s presentation during Hubble observations. The core fragment is not a sphere.

Scientists have a number of theories for how Psyche could have formed. It could be the remnant iron core of a protoplanet that was destroyed in a single catastrophic impact. It may be the remnant core of a protoplanet that lost its outer layers in heavy impacts that stripped off the surface but didn’t shatter the entire object. There are a number of theories about its formation, and the research to be done at Psyche will tell us a great deal about the early conditions of the solar system.

The asteroid belt doesn’t actually preserve the remnants of the ancient solar system as they once existed; the material present there today has been reworked and reworked in collision after collision. As we send spacecraft to asteroids like Vesta and dwarf planets like Ceres, we’ve begun to reconstruct the patterns of those collisions. We know now, for example, that a massive collision on asteroid Vesta a billion years ago is responsible for the high number of Vesta asteroids found on Earth.

These ultraviolet analyses of Psyche don’t confirm that the asteroid is an iron-rich core remnant, but they certainly don’t confirm it isn’t (other data gathered on Psyche, like its gravitational impact on other nearby bodies, suggest a very high density). Psyche is the only known metallic core-like body from any planet currently floating around and available to us to access. Put differently: Psyche may represent a scale model of the Earth’s core as it existed during planetary accretion, before gaining enough mass to become a planet.

This process may have failed at Psyche because of higher collision energies. One theory for why the asteroid belt failed to coalesce into a planet is that Jupiter kept gravitational energies too high to support planetary accretion, and the material of the belt was either ejected, pounded to dust, flung inwards (during the Great Heavy Bombardment), or swallowed by Jupiter itself.

The goals of the Psyche mission are to determine if Psyche represents a planetary core or a mass of previously unmelted material, to gather information on its age, to examine the compositional differences between the minerals in Psyche’s core and the expected contents of Earth’s, to determine the conditions under which it formed, and to characterize its overall topography.

There are currently no serious plans to mine Psyche, but if Earth were to begin to colonize the outer solar system (as shown in TV shows like The Expanse), there’s no question that we’d end up tapping the asteroid for material in one way or another. It’s a rock that could teach us about the earliest days of our solar system, while providing the raw materials we’ll need to create its future.

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