PROTOPLANET FORMS in the disk material circling a star, opening up a gap in the gas and dust from which it coalesces. In this model by Pawel Artymowicz of the University of Stockholm and his colleagues, the protoplanet is surrounded by a gravitational field, or Roche lobe, in which raw disk material accumulates, clumping together into a body that is recognizable as a massive planet.

Image: Pawel Artymowicz
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