Seeking Planets in the Dust

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Science  17 Feb 2006:
Vol. 311, Issue 5763, pp. 921
DOI: 10.1126/science.311.5763.921b

To understand planet formation in our solar system and beyond, astronomers search for dusty debris disks around stars like the Sun. Kalas et al. have spotted light scattered by low-mass disks around two stars that are close to a billion years old. In order to make these observations, the authors used the sensitive Advanced Camera for Surveys on board the Hubble Space Telescope; an inserted coronagraph mask permitted a clear field of view by blocking the stars' central glare.

The two disks have different shapes, due to distinct inclination and intrinsically different architectures. One appears as a narrow belt of dust, concentrated 83 astronomical units (AU) from the star, with an outer edge truncated abruptly at 109 AU. In contrast, the other star's disk extends out to 110 AU without significant narrowing, despite the old age of the star.

On the basis of these characteristics and those observed in similar studies, the authors propose two limiting classes of disk morphology: narrow belts and wide disks. The former could arise from early stochastic dynamical events that expel material and heat the disk, with nascent planets sweeping up the dust at certain radii, perhaps mirroring the early stages of our own solar system. The absence of these features in the wide disk morphology suggests that planet formation may not be ubiquitous in dust clouds. — JB

Astrophys. J. 637, L57 (2006).

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