Publ. Natl Astr. Observ. Jpn (in the press); preprint at http://arxiv.org/abs/1206.1215v1 (2012).

Planets form within circumstellar, or protoplanetary, disks made up of dust and gas left over from the formation of a star. The disk around the star UX Tauri A, in the constellation Taurus, might have a gap separating its inner and outer disks, which is suggestive of planet formation. Ryoko Tanii and co-workers have used the Subaru Telescope to image the 'pre-transitional' disk at infrared wavelengths. They find unusual polarization data — but no gap.

Normally, light scattering from small interstellar dust grains — typically 0.1 μm in size — is strongly polarized regardless of the scattering angle. However, in the case of UX Tauri A, the polarization varies from 2% to 66%. None of the existing scattering models for protoplanetary disks can explain the measured profile. What does work, however, is a geometric model based on a thin disk of non-spherical dust grains of 30-μm diameter. The authors suggest that repeated collisions cause the dust grains to stick together, forming irregular clumps on a timescale of 105 years. In other words, around UX Tauri A, a planetary object could be forming right now.