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Mercury Autumn 2009 Table of Contents

Spitzer Spots Clump of Planetary Material

NASA / JPL

Astronomers have witnessed odd behavior around a young star. Something, perhaps another star or a planet, appears to be pushing a clump of planet-forming material around. The observations, made with NASA's Spitzer Space Telescope, offer a
rare look into the early stages of planet
formation.

Planets form out of swirling disks of gas and dust. Spitzer observed infrared light coming from one such disk around a young star, called LRLL 31, over a period of five months. To the astronomers' surprise, the light varied in unexpected ways, and in as little time as one week. Planets take millions of years to form, so it's rare to see
anything change on time scales we humans can perceive.

One possible explanation is that a close companion to the star — either a star or a developing planet — could be shoving planet-forming material together, causing its thickness to vary as it spins around the star. "We don't know if planets have formed, or will form, but we are gaining a better understanding of the properties and dynamics of the fine dust that could either be-come, or indirectly shape, a planet," said James Muzerolle of the Space Telescope Science Institute, Baltimore, Md. "This is a unique, real-time glimpse into the lengthy process of building planets."

The observations showed that light from the inner region of the star's disk changes every few weeks, and, in one instance, in only one week. "Transition disks are rare enough, so to see one with this type of variability is really exciting," said co-author Kevin Flaherty of the University of Arizona, Tucson.

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