Simulated asteroid impacts give scientists a preview of what NASA's Psyche mission will find

Two hundred years after its discovery, asteroid 16 Psyche remains one of the solar system's most puzzling objects. At 140 miles in diameter, it is the largest known metallic asteroid - a dense, potato-shaped body orbiting in the main belt between Mars and Jupiter that might be the exposed core of a failed planet. Or it might be something else entirely. NASA is sending a spacecraft to find out, and researchers at the University of Arizona are not waiting for it to arrive before making predictions.

Testing origin stories with craters

The central question about Psyche is straightforward: what is it made of, and how did it get that way? Several competing hypotheses exist. Psyche could be the stripped core of a protoplanet - an early planetary body that differentiated into layers of metal and rock before violent collisions blasted away the rocky mantle, leaving the metal core exposed. Alternatively, it could be a mixed rubble pile - a body created by catastrophic impacts that jumbled metal and rock together. It might even be an ancient remnant that started out metal-rich and never differentiated at all.

Each scenario produces a different internal structure. And different internal structures should produce different-looking craters when an impactor hits.

Namya Baijal, a doctoral candidate at the Lunar and Planetary Laboratory, and her colleagues exploited this logic. Using the best available shape model of Psyche derived from telescope observations, they simulated the formation of a specific large concavity near the asteroid's north pole - roughly 30 miles across and three miles deep - under the competing interior models. Their results were published in JGR Planets.

The porosity variable nobody expected

The headline finding was not about composition but about empty space. Porosity - the fraction of an asteroid's volume that is void rather than solid material - turned out to strongly affect how craters form. Porous asteroids are crushable. When an impactor strikes, the energy is efficiently absorbed, producing deeper, steeper craters with less material ejected across the surface.

This matters because porosity is often ignored in impact simulations due to the difficulty of modeling it. But Baijal's results show it cannot be dismissed. The shape of a crater, the distribution of ejected debris, and the compression patterns in the subsurface all change significantly depending on how porous the target is.

By comparing simulated craters under different porosity assumptions with what the Psyche spacecraft actually observes, scientists will be able to constrain the asteroid's internal structure more precisely than composition measurements alone would allow.

A three-mile impactor at belt speed

The simulations used impactors about three miles across striking at roughly three miles per second - typical collision speeds for the asteroid belt. The team tested both a layered structure (metallic core with thin rocky mantle) and a uniform metal-silicate mixture. Both scenarios could reproduce the crater's known dimensions, meaning the crater shape alone will not settle the debate.

But the two models produce different secondary signatures - variations in subsurface density from impact compression, differences in how metal-rich debris distributes across the surface, and distinct ejecta blanket patterns. These are features the Psyche spacecraft's instruments can measure.

Looking at leftover pizza

Erik Asphaug, a professor in the Lunar and Planetary Laboratory and co-author, compared the approach to walking into an abandoned pizza parlor: the cooks have left, but you can examine the ovens, scraps of dough, and leftover toppings to infer how the pizzas were made. Asteroids are the leftovers of planet formation. We cannot reach the cores of Earth, Mars, or Venus, but Psyche might offer direct access to the core of an early planetary body.

If Psyche is an exposed core, it would provide the first direct window into a stage of planet formation that scientists have only been able to model theoretically. The violent collisional stripping of a protoplanet's mantle would have implications for understanding how the terrestrial planets in our own solar system assembled and differentiated.

Predictions before the data arrives

The Psyche spacecraft, led by Arizona State University with JPL managing operations, will arrive in 2029. It carries instruments to study the asteroid's surface composition, gravitational field, magnetic field, and bulk properties. The Arizona team's simulations provide a framework for interpreting what those instruments detect - not just for this one crater, but for the overall picture of Psyche's interior.

Adeene Denton, a postdoctoral researcher and co-author, noted that by rigorously treating Psyche's shape, porosity, and composition, this work represents a significant advance in the capacity to realistically simulate impacts into unusual asteroid types.

When the spacecraft data arrives, the geochemists, geologists, and modelers on the mission team will all be examining the same object from different angles. Having testable predictions in hand before the first images come back gives the entire collaboration a head start on one of the solar system's oldest puzzles.