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This massive crater could expose the heart of a lost planet

A mysterious metal asteroid may finally reveal whether it’s a lost planet’s core — or something even stranger.

Date:

March 17, 2026

Source:

University of Arizona

Summary:

A mysterious metal-rich asteroid called Psyche has been baffling scientists for over two centuries, and its true origin remains one of the biggest unanswered questions in planetary science. Is it the exposed core of a failed planet, or a chaotic mix of rock and metal forged through countless violent collisions? To find out, researchers simulated how a massive crater near Psyche’s north pole formed, revealing that the asteroid’s internal “porosity” — how much empty space it contains — may hold the key to its secrets.

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This illustration, created in March 2021, depicts asteroid Psyche, which lies in the main asteroid belt between Mars and Jupiter. Psyche is the focal point of NASA's mission of the same name. Credit: NASA/JPL-Caltech/ASU

More than two centuries after asteroid 16 Psyche was first identified, scientists are still trying to determine how it formed.

Located in the main asteroid belt between Mars and Jupiter, Psyche ranks as the 10th-most massive asteroid and the largest known object made primarily of metal, measuring about 140 miles across. NASA's Psyche spacecraft is scheduled to arrive in 2029 with the goal of uncovering its origin. Researchers suspect it could be a remnant of an early planet that was torn apart by massive collisions, or possibly a fragment of a once-layered body that lost its outer rocky shell.

Other ideas suggest Psyche may have formed as a metal-rich object from the start, or that it became a mix of rock and metal after repeated impacts with other asteroids. Each possibility points to a different story about how planets formed in the early Solar System.

Simulating Craters to Reveal Psyche's Interior

To explore these possibilities, scientists at the University of Arizona's Lunar and Planetary Laboratory created simulations to understand how a large crater near Psyche's north pole may have formed. Their findings, published in JGR Planets, provide predictions that will help researchers interpret data collected by NASA's Psyche mission when it arrives. By combining these simulations with real observations, scientists hope to finally determine what Psyche is made of.

"Large impact basins or craters excavate deep into the asteroid, which gives clues about what its interior is made of," said Namya Baijal, a doctoral candidate at the LPL and first author of the paper. "By simulating the formation of one of its largest craters, we were able to make testable predictions for Psyche's overall composition when the spacecraft arrives."

Although metal-rich asteroids make up less than 10% of the main belt, Psyche is the largest among them. Still, researchers will need direct spacecraft measurements to understand how that metal is distributed throughout its interior.

Why Porosity Matters in Asteroid Impacts

"One of our main findings was that the porosity -- the amount of empty space inside the asteroid -- plays a significant role in how these craters form," said Baijal. "Porosity is often ignored because it's difficult to include in models, but our simulations show it can strongly affect the impact process and shape of craters left behind."

Asteroids with more internal voids tend to absorb impact energy more effectively, which leads to deeper and steeper craters and less debris scattered across the surface. By comparing simulated crater features with those observed by the spacecraft, scientists can test whether Psyche's interior is layered, with distinct metal and rock regions, or instead a more chaotic mixture of materials.

Clues to Planet Formation in the Early Solar System

The research team compares their approach to examining the remains of an abandoned pizza shop. Psyche and other main belt asteroids are thought to be leftover building blocks from planet formation. "The cooks have long left, but you can look at what's left behind -- the ovens, scraps of dough, the toppings -- and make inferences about how the pizzas were made," said Erik Asphaug, a professor in LPL and co-author of the study. "We can't get to the cores of Earth or Mars or Venus, but maybe we can get to the core of an early asteroid."

If Psyche turns out to be the exposed core of a former planet, stripped of its outer layers, it would provide rare insight into a violent phase of planetary evolution that is otherwise impossible to observe directly.

"We tested two main interior structures for Psyche," said Baijal. "One is a layered structure with a metallic core and a thin, rocky mantle, which likely formed if a violent collision stripped away the outer layers. The other is a uniform mixture of metal and silicate, created by a more catastrophic impact that mixed everyth