Using the Atacama Large Millimeter/submillimeter Array (ALMA), astronomers have detected the emission from 13CO — measure of the molecular gas distribution — in a circumplanetary disk embedded in the protoplanetary disk of the T Tauri star AS 209.
Artist’s impression of an infant star still surrounded by a protoplanetary disk in which planets are forming. Image credit: L. Calçada / ESO.
“As a giant planet forms, it opens a gap in its parent circumstellar disk,” said University of Florida’s Professor Jaehan Bae and colleagues.
“Within the Hill sphere (gravitational sphere of influence) of the planet, a circumplanetary disk forms in order to conserve the angular momentum of the material accreted from the circumstellar disk.”
“The growth of a planet after gap opening is controlled by gas accretion through its circumplanetary disk.”
“Circumplanetary disks also play a crucial role in satellite formation. Indeed, the prograde, nearly circular, and coplanar orbits of regular satellites of Jupiter and Saturn suggest that their formation must have happened within circumplanetary disks.”
“Despite their importance, however, many attempts to search for circumplanetary disks have yielded nondetections, and the detections made to date are limited in millimeter continuum observations.”
“Consequently, fundamental properties of circumplanetary disks, such as their sizes and whether they are indeed rotationally supported ‘disks’ or instead pressure-supported envelopes are not fully understood.”
The 13CO emission (blue contours) in a circumplanetary disk embedded in the protoplanetary disk of AS 209. Image credit: Bae et al., doi: 10.3847/2041-8213/ac7fa3.
The astronomers used ALMA to observe AS 209, a star located in the outskirts of the Ophiuchus star-forming region at a distance of 395 light-years.
Also known as IRAS 16464-1416 and PDS 92, this star has mass of 1.2 solar masses and an age of 1-2 million years.
While studying AS 209, the scientists detected a blob of emitted light in the middle of an otherwise empty gap in the gas surrounding the star.
That led to the discovery of the circumplanetary disk surrounding a potential Jupiter-mass planet, which is located more than 200 AU away from the host star.
“The best way to study planet formation is to observe planets while they’re forming,” Professor Bae said.
“We are living in a very exciting time when this happens thanks to powerful telescopes, such as ALMA and the NASA/ESA/CSA James Webb Space Telescope.”
A paper on the findings was published in the Astrophysical Journal Letters.
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Jaehan Bae et al. 2022. Molecules with ALMA at Planet-forming Scales (MAPS): A Circumplanetary Disk Candidate in Molecular-line Emission in the AS 209 Disk. ApJL 934, L20; doi: 10.3847/2041-8213/ac7fa3
