Always interesting to see ideas make Nature (or a Nature-family journal):
Park, R. S. Ermakov, A. I. Konopliv, A. S. et al. A small core in Vesta inferred from Dawn’s observations
s41550-025-02533-7
We thought we had the story: Asteroid (4) Vesta was big enough to retain its heat of formation. It then melted, becoming a magma world. This magma world then split into a heavy core and light crust, with the intermediate-density mantle in the intermediate position. We call this process “differentiation.” After all, Vesta’s surface has crust-type rocks, depleted of core-type material like iron. Right? Riiight?
Park et al. are now shaking up geophysics world: they say our picture of Vesta is (at least partially) wrong. The Dawn probe orbited Vesta from mid-2011 to late-2012. Not only did the craft return radio science (the doppler shift of its transmitted signal), but the cameras aboard Dawn tracked Vestan features and their positions. By using both gravity signals and feature tracking, Park et al. derive Vesta’s gravity field and internal structure. Besides direct tugging, the internal makeup of Vesta affects its nutation and precession- slight imperfections of Vesta’s daily rotation. Nutation and precession change where surface features “should” be, based on normal rotation.
The claim is a bold one: reassessing the Dawn results, Park et al. find that Vesta is only partially differentiated, and its layers are more similar in density than the differentiation idea would have us believe. How is this possible? Park et al. conjecture that somehow, the heating process never got up to full steam. Alternately, Vesta formed from rocks that didn’t have the separate components: there simply wasn’t the core material (iron and iron-soluble elements) in the first place. One way to accomplish this is to form Vesta as a second-generation Solar System object, not primordial.
Again, this is a bold claim. We’ll wait a while, and see if anyone publishes a response paper, shooting down this result. Or there may be a competing hypothesis, which better fits the evidence.