In DepthAstronomy

Hints of young planets puzzle theorists

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Science  21 Dec 2018:
Vol. 362, Issue 6421, pp. 1337
DOI: 10.1126/science.362.6421.1337

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HL Tau, a mere stripling of a star at no more than 1 million years old, was swaddled in a surprise. Four years ago, the Atacama Large Millimeter/submillimeter Array (ALMA) in Chile revealed rings and gaps in a bright disk of dust around HL Tau—apparently swept clean by unseen planets that had formed millions of years earlier than astronomers thought possible. But now, an ALMA survey of 20 disks around nearby young stars suggests the precocious planets around HL Tau are no anomalies. The results, published in 10 papers last week in The Astrophysical Journal Letters, suggest disks with rings, gaps, and other features are the norm, not an exception—a result that will keep theorists busy for years.