Astronomers See Moons Forming in Disk Around Distant Exoplanet - The New York Times

Scientists have never before gotten such a clear view of moons in the making.

To date, astronomers have discovered 4,438 worlds orbiting other stars, and there is no doubt that diverse moons dance around most of these exoplanets.

Now, after years of observations of a pair of Jupiter-like exoplanets nearly 400 light-years from Earth, astronomers have found the next best thing: a disk of debris orbiting one of these worlds, a ring of rock and gas gradually coalescing under its own gravity.

The star-encircling disk of gas and dust that made its two Jupiter-like planets, PDS 70b and PDS 70c, is still present.

As new planets are slowly pieced together, the two youths that already exist continue to siphon off this disk’s debris and fortify themselves with it.

A month later, scientists using Chile’s Atacama Large Millimeter/submillimeter Array (ALMA) reported that radio waves emitted by fine dust were emanating from around PDS 70c — promising evidence that a moon-making debris disk surrounded it.

Benisty and her colleagues used ALMA to conduct follow-up observations, demonstrating with little doubt that PDS 70c has its own disk of debris, one substantial enough to make three moons the size of Earth’s satellite.