In 2014, the Atacama Large Millimeter/submillimeter Array (ALMA) in Chile recorded a "revolutionary" image of a young star surrounded by an incredibly detailed system of dust rings. Why was this revolutionary? Well, it was the clearest evidence yet of a star birthing baby planets from its protoplanetary disk.
ANALYSIS: 'Revolutionary' New View of Baby Planets Forming Around a Star
But just because the star, called HL Tauri, has a system of rings separated with apparently empty gaps, it doesn't necessarily prove that young exoplanets are inside those gaps, vacuuming up the dust. Key to this ambiguity was that HL Tauri is really young -- only one million years old -- and not thought to be capable of forming planets at such an early stage, according to planetary formation models at least.
Now, ALMA has revisited the stellar beauty, this time observing emissions from HCO+ gas molecules, not from the dust itself. The theory is this: Should there be baby planets forming in those dust gaps, the gas distribution in the star's protoplanetary disk should also display a similar pattern of rings. The planetary gravities would suck up dust and gas in equal measure. If baby planets aren't the cause, the HCO+ gas distribution should be uniform with no ring-like features.