It is no small task to build a moon. First, a planet has to be massive enough to pull in passing space detritus — some dust here, some gas there, maybe a few asteroids — and eventually let them congeal on their own into a celestial body.
That was, at least, the prevalent theory among astronomers regarding the formation of moons. Notably, scientists had never observed a moon-forming area (also known as a circumplanetary disc) outside of our solar system until recently. That is no longer the case, as a new study published in the journal Astrophysical Journal Letters demonstrates.
With enough gas and dust to support three moons the size of the one orbiting Earth, the newly discovered circumplanetary disc is nearly 500 times the size of Saturn’s rings. Rotating around the planet PDS 70c, the disc may reveal new insights into the formation of satellites (the scientific word for things such as moons).
“Our analysis demonstrates a disc in which satellites may be growing,” Myriam Benisty, the paper’s principal author and a researcher at Grenoble University in France and the University of Chile, noted in the same statement. The researchers observed the disc with the Atacama Large Millimeter/submillimeter Array (ALMA) telescope at the European Southern Observatory (ESO) in Chile “at such exquisite resolution that we could clearly identify the disc as being associated with the planet and constrain its size for the first time.”
“More than 4,000 exoplanets have been discovered to date, but they have all been discovered in mature systems,” said Miriam Keppler, a co-author of the study and a researcher at the Max Planck Institute for Astronomy. PDS 70c and its companion, PDS 70b, “create a system similar to the Jupiter-Saturn pair” and are “the only two exoplanets discovered thus far that are still forming.”
PDS 70b, the planet’s twin, sheds light on another way in which this finding can aid astronomers. Along with assisting us in comprehending how moons are generated, the fact that both planets are so young implies that we can learn a great deal from studying their activities. Scientists have a variety of hypotheses about how planets evolved, and circumplanetary disc observations may help us learn more about planets’ early lives, just as they may inform us about the origins of moons.
These new findings are also critical for establishing hitherto untested hypotheses of planet formation, “Jaehan Bae, another co-author and an astronomer at the Carnegie Institution for Science, said in a release.