Building a moon is not an easy task. A planet must be large enough to absorb space debris — some dust, some gas, and maybe some asteroids — and then let these particles congeal into a celestial body.
Astronomers believed that this was the best theory to explain how moons form. However, scientists have not yet observed a moon-forming area (also called a circumplanetary disc) outside of the solar system. This is now changing with the publication in Astrophysical Journal Letters of a new study.
The newly discovered circumplanetary disk, which contains enough gas and dust for three moons twice the size of the one orbiting Earth’s surface, is approximately 500 times larger than Saturn’s rings. The disk rotates around PDS 70c, which could give scientists new insight into the formation of satellites (the scientific name for objects such as moons.
“Our work presents a clear detection of a disk in which satellites could be forming,” Myriam Benisty, the lead author of the paper and a researcher at the University of Grenoble, France, and at the University of Chile, added in the same statement. Using the Atacama Large Millimeter/submillimeter Array (ALMA) telescope, based at the European Southern Observatory (ESO) in Chile, the researchers observed the disk “at such exquisite resolution that we could clearly identify that the disk is associated with the planet and we are able to constrain its size for the first time.”
“More than 4,000 exoplanets have been found until now, but all of them were detected in mature systems,” Miriam Keppler, a co-author of the study and researcher at the Max Planck Institute for Astronomy, said in a statement. “ PDS 70c, and its counterpart PDS 70b form a system that is similar to the Jupiter-Saturn couple and are “the only exoplanets currently in formation.”
PDS 70b, the planetary sibling, provides insight into another way this discovery can benefit scientists. We could also learn more about how the moons formed from their activity, as both planets are young. Scientists have many theories about how planets formed. The circumplanetary disk observation could be used to help scientists understand the early lives and origins of planets.
“These observations are also extremely important for proving theories of planet formation that couldn’t be tested up until now,” Jaehan Be, another coauthor and an astronomer from the Carnegie Institution for Science stated in the statement.