First Moon-Forming Disk Detected Swirling Around an Exoplanet

Telescope observations suggest that a cloud of gas and dust around a planet 370 light-years away may be coalescing into planet-sized moons

Moon Clouds

Last month, astronomers announced that they’d snapped a rare image of two planets forming around a young, 6-million-year-old star about 370 light-years away called PDS 70. Now, after closer examination, they’ve found something even more surprising: the first evidence of a moon-forming disk around one of those planets, PDS 70c.

The two planets were found using the European Southern Observatory’s Very Large Telescope (VLT) which can detect the glow of hydrogen in gas clouds. The observations allowed researchers to find the planets PDS 70b and PDS 70c, both of which are as large or larger than Jupiter, plowing through a debris cloud around their star called a circumstellar disk and producing a detectable gap in the gas and dust.

In the new study in The Astrophysical Journal Letters, researchers trained the Atacama Large Millimeter/submillimeter Array (ALMA), a group of 66 dish antennas based in northern Chile, on the PDS 70 system. The telescope can detect very faint radio waves given off by fine dust. By combining those new observations with the VLT data and optical telescope images, the team believes that a cloud of dust also surrounds the planet PDS 70c, and that it is currently in the process of forming planet-sized moons.

“For the first time, we can conclusively see the telltale signs of a circumplanetary disk, which helps to support many of the current theories of planet formation,” lead author Andrea Isella from Rice University says in a press release. “By comparing our observations to the high-resolution infrared and optical images, we can clearly see that an otherwise enigmatic concentration of tiny dust particles is actually a planet-girding disk of dust, the first such feature ever conclusively observed.”

The astronomers estimate that 70c is about 1 to 10 times the mass of Jupiter, and the data suggests that it is already a fully formed planet, though it may still be pulling gas onto its surface. Though the data did not reveal any conclusive signs of fully formed moons, Isella says it’s possible that planet-sized moons are orbiting 70c somewhere in its dust cloud.

The finding supports planet and moon formation hypotheses that researchers have had for years. But this is one of the first times astronomers have, possibly, seen the process in action. “Planets form from disks of gas and dust around newly forming stars, and if a planet is large enough, it can form its own disk as it gathers material in its orbit around the star,” Isella tells Ashley Strickland at CNN. “Jupiter and its moons are a little planetary system within our solar system, for example, and it’s believed Jupiter’s moons formed from a circumplanetary disk when Jupiter was very young.”

While the detection of a dusty moon cloud around 70c is promising, further observations are required to confirm the finding. Sean Andrews of the Harvard-Smithsonian Center for Astrophysics, who was not involved in the study, tells Nadia Drake at National Geographic that he is optimisic about the finding, though the data is a little wonky. For instance, the ALMA results show a point that is planet PDS 70c in the middle of the dust disk, but when viewed in infrared wavelengths, PDS 70c becomes much less solid. “There are certainly some puzzling aspects of these results,” he says. “The environment around ‘c’ appears pretty complicated.”

Isella agrees that the signal from 70c is faint and requires further study. The team is planning to use ALMA and other scopes to reobserve the PDS 70 system and learn more about the observed planets, moons and their orbits.

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