Astronomers detect moon-forming disc around exoplanet for the first time

This image, taken with the Atacama Large Millimeter/submillimeter Array (ALMA), in which ESO is a partner, shows wide (left) and close-up (right) views of the moon-forming disc surrounding PDS 70c, a young Jupiter-like planet nearly 400 light-years away. (ALMA (ESO/NAOJ/NRAO)/Benisty et al./Handout)

TORONTO — Astronomers have detected the presence of a disc around a planet outside our solar system for the first time.

Using the Atacama Large Millimetre/submillimeter Array (ALMA) observatory which is partially run by the European Southern Observatory (ESO), astronomers saw the disc, called a “circumplanetary disk,” surround the exoplanet PDS 70c, one of two giant Jupiter-like planets orbiting a star nearly 400 light-years away.

Researchers had found hints of a disc being formed around PDS 70c before, according to a release, but could not get a clear enough image to support their theory, until now. Their findings were published in The Astrophysical Journal Letters on Thursday.

"Our work presents a clear detection of a disc in which satellites could be forming," said study author Myriam Benisty in the release. "Our ALMA observations were obtained at such exquisite resolution that we could clearly identify that the disc is associated with the planet and we are able to constrain its size for the first time.”

Using ALMA, Benisty and the team found that the disc has approximately the same diameter as the distance from our Sun to the Earth and enough mass to form up to three satellites the size of the Moon.

"These new observations are also extremely important to prove theories of planet formation that could not be tested until now," said study author Jaehan Bae.

Planets form in dusty discs around young stars, carving out space as they collect material from the disc to grow. In this process, a planet can acquire its own circumplanetary disc, which contributes to the growth of the planet by regulating the amount of material falling onto it.

At the same time, the gas and dust in the circumplanetary disc can come together into progressively larger bodies through multiple collisions, ultimately leading to the birth of moons.

But astronomers do not yet fully understand the details of these processes. "In short, it is still unclear when, where, and how planets and moons form," said ESO researcher Stefano Facchini, in the release. "This system therefore offers us a unique opportunity to observe and study the processes of planet and satellite formation.”

Exoplanets PDS 70b and PDS 70c, the two planets making up the system, were first discovered using ESO's Very Large Telescope (VLT) in 2018 and 2019, respectively. The latest high-resolution ALMA observations have now allowed astronomers to gain further insights into the system.

For instance, researchers found that because PDS 70b does not have clear evidence of a disc, it was probably starved of material because of PDS 70c forming its own.

Researchers hope to continue their study using the ESO’s high-resolution Extremely Large Telescope, currently under construction on Cerro Armazones in the Chilean Atacama desert.