NASA’s Psyche mission to a metal asteroid may reveal how Earth formed

NASA is preparing to launch a mission to a one-of-a-kind asteroid called Psyche – which may actually be the exposed metal core of what was once a young planet. The mission, also called Psyche, is scheduled to launch on 13 October.

The asteroid Psyche takes about five Earth years to complete an orbit around the sun, and the closest it gets to Earth is about three times the distance between our planet and Mars. Because of its distance and relatively small size – less than 300 kilometres across at its widest point – we have very few observations of it and know almost nothing about its surface, its origins, or even its composition.

What we do know is that it’s probably almost all metal, most of which is likely iron. While the potential value of all of that metal has made headlines, bringing it back to Earth is not in this mission’s remit. “We have no technology to bring this back, and even if we did manage to bring it back to Earth it would probably be a catastrophic mistake for the planet because we don’t know how to park something in orbit,” says Psyche principal investigator Linda Elkins-Tanton at Arizona State University.  “This asteroid is just for scientific exploration, not for profit.”

Because we know so little about Psyche, there are very few limitations on what we could discover. We’ve never even seen an object of this type up-close before. Even our limited ideas of what Psyche is have changed in recent times thanks to remote observations suggesting that it may carry more silicate minerals than previously expected.

“Who knows what it looks like? We have literally no idea,” says Elkins-Tanton. The surface is sure to look different from rockier asteroids we’ve seen in the past, she says: “When we do craters in metal in the laboratory, weird things happen. You could get these spikes and this kind of sand of metal ball bearings across the surface and scarps and cliffs that are different from what we see on rocky worlds.”

Metallic objects like Psyche could be a key ingredient in the formation of rocky worlds like our own. Earth and other terrestrial planets host iron cores, but we’ve never been able to study one in detail because they are so deep underground. The Psyche mission may be our first chance to see a planetary core directly.

“We are so attached as a species to rocky planets, but the one missing ingredient that we have never been able to inspect up close is the metal core,” says Elkins-Tanton. “It’s like we’re making cakes and we’ve never met an egg before. Now we’re going to go meet an egg.”

If all goes well with the launch, the spacecraft is expected to arrive at Psyche in 2029. It carries four scientific instruments: A camera, a spectrometer to measure the asteroid’s composition, a magnetometer to examine its magnetic field, and a telecommunications system that will double as a way to measure Psyche’s gravity field and internal structure. Hopefully, those instruments will tell us what exactly Psyche is, how it formed, and how it relates to the iron core at the centre of Earth.