Around which PDS 70 planet was the first moon-forming circumplanetary disk detected? It was PDS 70c.
PDS 70 is a young star about 370 light-years away in the constellation Centaurus. It is surrounded by a broad protoplanetary disk, with a large gap carved by forming planets. The two known giant planets, PDS 70b and PDS 70c, orbit within that gap.
Astronomers detected millimetre-wavelength emission associated with PDS 70c, interpreting it as dust in a circumplanetary disk. Such a disk is the material reservoir from which moons may assemble, much as planets form from a disk around a young star. Later observations strengthened the case that the disk surrounds c rather than being unrelated material in the wider stellar disk.
A common mix-up is PDS 70b: researchers also reported evidence for a circumplanetary disk around b, but the landmark first detection described as a moon-forming disk was associated with PDS 70c. The discovery gave astronomers a rare view of satellite formation around a planet outside the Solar System.