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A case of arrested development

The results are published in a series of three papers in the journals Science and Planetary Space Science (PSS).

Benjamin Weiss, an associate professor of planetary sciences in MIT’s Department of Earth, Atmospheric and Planetary Sciences, says a melted core within Lutetia may exemplify a “hidden diversity” within the greater asteroid belt.

“There might be many bodies that have cores and interesting interiors that we never noticed, because they’re covered by unmelted surfaces,” says Weiss, who is a co-author on both Science papers and lead author for the paper in PSS. “The asteroid belt may be more interesting than it seems on the surface.”

Most asteroids careening through the asteroid belt, between the orbits of Mars and Jupiter, are scrambled versions of their former selves: essentially mashed-up masses of rock and metal that have collided and cooled over billions of years. These rocky conglomerations are relatively small and light, with voids and cracks in their interiors that make them very porous. It had been thought that the vast majority of these bodies never melted to form dense, metallic cores, but instead are just primordial piles of space rocks and dust.

In contrast, the Rosetta team — led by Holger Sierks of the Max-Planck Institute for Solar System Research and Martin Pätzold of the Rheinisches Institut für Umweltforschung, both in Germany — found that Lutetia is extremely dense. The team drew up a model of the asteroid’s shape, based on images taken by the Rosetta probe. The researchers then calculated Lutetia’s volume, mass and finally its density, which they found, in collaboration with the MIT team, to be greater than most meteorite samples measured on Earth.