For years, scientists believed Vesta, one of the biggest objects in the asteroid belt, was more than just an asteroid.
They thought it had layers like a small planet—a crust, mantle, and metal core. But new research has turned that idea upside down.
A study led by NASA’s Jet Propulsion Lab, with help from Michigan State University, has found that Vesta does not have a core after all.
This surprising discovery challenges the long-held belief that Vesta was a “protoplanet” that just didn’t grow into a full-sized planet.
“The lack of a core was very surprising,” said MSU’s Assistant Professor Seth Jacobson, who helped write the study published in Nature Astronomy.
“It’s a really different way of thinking about Vesta.”
So, what is Vesta really? Scientists have two main ideas. The first is that Vesta started to develop layers but didn’t finish the process, called “incomplete differentiation.”
The second idea, which Jacobson had suggested years ago, is that Vesta could actually be a broken piece of a young planet that was still forming.
Most asteroids are made of old, loose material from the early solar system. But Vesta’s surface is covered in solid volcanic rock, suggesting it once went through melting like planets do. NASA’s Dawn spacecraft, launched in 2007, visited Vesta in 2011–2012, gathering detailed maps and measuring its gravity to learn more about its inside. For years, scientists puzzled over some strange data from Dawn’s mission.
Recently, Ryan Park, a senior scientist at JPL, decided to reprocess the Dawn data using better techniques. This updated analysis showed that Vesta’s spin and gravity field didn’t match what you would expect if it had a heavy metal core. This finding hints that Vesta’s history is much more complicated than once thought.
One way scientists figure out if a planet or asteroid has a core is by studying how it spins—similar to how a figure skater changes speed by moving their arms. Vesta’s movement suggested it doesn’t have a dense center at all.
Still, there are questions. If Vesta never finished developing a core, why do meteorites from Vesta seem to show that it fully melted? And if Vesta is a piece of a shattered young planet, which planet was it?
Jacobson and his team are now creating new models to explore these possibilities. They also plan to take a fresh look at meteorites from Vesta with this new information in mind.
“This study is just the beginning,” Jacobson said. “We might be looking at ancient pieces of a planet that never had the chance to fully form. And we don’t even know yet which planet it could have been.”
