New study suggests Vesta isn't a protoplanet but a chunk of an ancient, lost world.
Asteroid Vesta may be debris from a larger planet shattered billions of years ago
Asteroid Vesta, long considered a stalled protoplanet, may actually be a massive fragment of a larger world that once existed in our solar system. New findings based on gravity-field mapping and spin-rate data suggest Vesta lacks the dense core typically found in differentiated planetary bodies. The discovery challenges previous assumptions, drawn from NASA's Dawn mission in 2012, that classified Vesta as an embryonic planet. Now, scientists report that Vesta might have been ejected from a differentiated world in a massive collision 4.5 billion years ago, upending ideas about the development of planets and asteroids.
New Gravity Data Suggests Vesta Is Debris from a Destroyed Planet, Not a Protoplanet
As per a new study published in Nature Astronomy on April 23, 2025, Vesta does not quite match the former model. Refined calibration methods polished the radio Doppler signals, confirming the absence of a metal-rich core, which was inconsistent with earlier work. Seth Jacobson of Michigan State University, who led the research, stated the new interpretation marks a major shift in planetary science. While Vesta's basaltic, volcanic surface still indicates geological activity, its internal uniformity contradicts the expectations of a body that once underwent full differentiation.
This paradox has caused scientists to reconsider the asteroid's heritage. One scenario is that Vesta started to differentiate but never got very far. But data from meteorites called howardite-eucrite-diogenites (HEDs), thought to have come from Vesta, show no signs of such incomplete differentiation. Jacobson and his team instead favour the explanation that Vesta was formed from material blasted off a fully developed planet during an ancient planetary collision, which could also illustrate its volcanic surface without requiring it to have a dense core.
The results not only question Vesta's identity but also suggest a possibility of a more general theory: that other asteroids could also be pieces of shattered planets. NASA's Psyche and ESA's Hera missions, planned for the next decades, intend to do such gravity investigations, which could ultimately confirm this new view. Jacobson noted that Vesta's composition could even hint at a shared origin with Earth or other early planets, a hypothesis that may reshape asteroid science entirely.
