Missing: Several Large Planets

Missing: Several Large Planets

Nearly a year ago, the ALMA collaboration released this stunning image of the young star HL Tau. The sub-millimeter wavelengths of light that ALMA detects revealed a vast disc of gas and dust, several times larger than Neptune’s orbit. Intriguingly, the disc was divided up into a series of well-defined, concentric rings.

The cause of the rings seemed clear: There must be planets around HL Tau, their gravity sculpting the gas and sweeping out the dark gaps in the disc.