Astronomers confirm discovery of lunar disk around young exoplanet

Two years ago, astronomers spotted an apparent circumplanetary disk around a planet outside of our solar system, but they couldn’t be sure. Follow-up observations now show they were right, in a discovery that could improve our understanding of exomouns and their formation in emerging star systems.

Protoplanet PDS70c has a circumplanetary disk, according to news research published in The Astrophysical Journal Letters. Scientists thought as much in research released two years ago, but they were unable to distinguish the disc from its surrounding environment, leaving room for doubt. The follow-up observations made by the Atacama Large Millimeter / Sub-Millimeter Array (ALMA) in Chile were key to confirmation.

“Our ALMA observations were obtained at such exquisite resolution that we were able to clearly identify that the disk is associated with the planet and we are able to constrain its size for the first time,” astronomer Myriam Benisty explained in a communicated. Benisty, who led the study, is a researcher at the University of Grenoble, France, and at the University of Chile.

By observing the system in submillimeter light (a wavelength parked between the microwave and infrared part of the spectrum), the team was able to confirm the presence of copious amounts of dust orbiting PDS70c. The disk, if it were located in our solar system, would extend from the center of the Sun at a distance slightly beyond Earth’s orbit.

This Jupiter-like protoplanet, along with its equally gigantic sibling, PDS70b, orbits a young, 5 million-year-old star located at 370 light-Earth years. The star itself houses a circumstellar disc, inside which the two protoplanets suck up matter, creating pockets or cavities around them. PDS70b and PDS70c are both gas giants, and both are far from their host star, at distances of 22 AU and 34 AU, respectively. By comparison, Neptune is 30 AU of our Sun, with 1 AU being the average distance of Earth to the Sun.

The circumplanetary disk around PDS70c is about 500 times the size of Saturn’s rings, and, as the new article points out, the amount of mass in this disc could form up to three exmoons the size of ours Moon.

Interestingly, the new research rules out a circumplanetary disk around PDS70b. Scientists say his greedy brother, PDS70c, is not a good sharer, and has gobbled up the necessary building material for himself.

“This system”, according to Stefano Facchini, co-author of the article and researcher at the European Southern Observatory, “offers us a unique opportunity to observe and study the processes of formation of planets and satellites”.

Indeed, the confirmation of a circumplanetary disk around PDS70c could bring new clarity to current theories on exmoons and their formation. In one possible scenario, the protoplanets steal the mass of the surrounding circumstellar disk, and the resulting mass drops fall on the forming planet. But some pieces of matter remain in orbit, clumping together to form natural satellites.

It is a fascinating discovery, but the team is not yet done with the PDS70 system. They are already eagerly awaiting ESO’s extremely large telescope, which is currently under construction in the Atacama Desert in Chile. Using this tool, astronomers hope to acquire even higher resolution scans of the system. and constructing three-dimensional views showing the gas moving through the circumplanetary disk.

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