Gas Giant Formation Caught in the Act

Illustration of the disc and gas streams around young star HD 142527. Saturn and Jupiter are examples of gas giants---huge, uninhabitable planets composed of gas rather than solid matter. Based on observations of these planets and models of their evolution, astronomers have long believed [pdf] that they form by guzzling gas from young stars. This week, courtesy of a telescope in the deserts of Chile, astronomers reported seeing the first direct evidence of gas giant formation. Astronomers were observing a young star called HD 142527, some 450 light years from Earth. Like most young stars, HD 142527 is surrounded by a disk of gas and dust---remnants of the star's conception that continue to circle the star for millions of years. But there was something strange about this particular star's disk. Astronomers observed a large gap in the gas and dust, which, as reported in Nature this week, they believe is caused by an up-and-coming gas giant. The gap tipped astronomers off, but confirmation came in the form of telltale gas streams. The ALMA telescope's glare-resistance and ability to see finer detail gave astronomers a never-before-seen view of these key features of the planet-forming process. It goes like this: As the planetary precursor orbits its star, it mooches off the star's remaining building materials, gathering gas and dust into its own growing form. But the star doesn't just stand by and let this happen; it would be a short-lived star if it did. The star's gravity pulls gas from the outer reaches of the star's disk, through the gap cleared by the gas giant, and into the innermost part of the disk to sustain the star. This is the first time astronomers have actually seen these streams, whose existence up to this point has been theoretical. Gas giants like these form within the first few million years of their star's birth, so these new visions of the process add to the picture of our own solar system's dramatic early days. Image courtesy of S. Casassus et al. / ALMA (ESO/NAOJ/NRAO)