Possible moons in formation around the exoplanet PDS 70 c


An article published in the journal “The Astrophysical Journal Letters” reports the observation of what is interpreted as a circumplanetary disk in the system of the young star PDS 70. A team of researchers led by Andrea Isella of Rice University in Houston, Texas, used the ALMA radio telescope to detect the emissions of that disk that surrounds the exoplanet PDS 70 c and according to the astronomers is of the type that controls the formation of planets and of a system of moons such as those around the planet Jupiter.

Approximately 370 light years from Earth, the PDS 70 star system is still in its formation phase so, after a protoplanetary disk was identified in 2006, it became the object of a number of researches. Two articles published in July 2018 in the journal “Astronomy & Astrophysics” reported the discovery and description of a giant gas planet being formed in that system, named PDS 70 b.

In June 2019 an article published in the journal “Nature Astronomy” reported the observation of two protoplanets in the PDS 70 system, adding the discovery of a second exoplanet that was cataloged as PDS 70 c using the MUSE instrument mounted on ESO’s Very Large Telescope (VLT). Now another team of researchers used the ALMA radio telescope (Atacama Large Millimeter/submillimeter Array), inaugurated in March 2013, for follow-up studies on that system. Combining the radio emission data from the gas particles around the star PDS 70 and the optical and infrared wavelength data detected by the VLT, the result is that there seems to be a circumplanetary disk around the newly discovered exoplanet that could form moons.

The top composite image (ALMA (ESO/NOAJ/NRAO) A. Isella; ESO) brings together the data of ALMA with those of MUSE and also of SPHERE, another instrument mounted on the VLT, to show the PDS 70 system with the two exoplanets and the materials surrounding the exoplanet PDS 70 c. The infrared brightness and the bands that carry the “signature” of hydrogen have convinced that it is a planet already formed and that the nearby gas continues to be attracted to it and for some time it will grow a little more. At the same time, that gas and other materials around the planet could form a system of moons.

As for the first planet discovered in that system, the mass estimates for PDS 70 c are still vague, between 1 and 10 times that of Jupiter. Andrea Isella pointed out that if the actual mass is close to the estimated top limit it’s possible that there may be planet-sized moons in their formation phase and this would make it easier to identify them with new observations by ALMA that the researchers intend to conduct to map the planets’ orbits, the concentration and movements of dust in the system.

Nowadays there are many cases of solar systems in formation known with exoplanets in various formation stages. However, the next frontier of star systems astronomy is that of exomoons so the discovery of a possible circumplanetary disk is really interesting but it would be the first of that type and consequently needs further confirmation. The observations provide different images depending on the wavelengths detected, therefore more observations over time are crucial to better understand the situation in the area of ​​the exoplanet PDS 70 c.

Artist impression of the exoplanet PDS 70 c and its circumplanetary disk (Image NRAO/AUI/NSF, S. Dagnello)
Artist impression of the exoplanet PDS 70 c and its circumplanetary disk (Image NRAO/AUI/NSF, S. Dagnello)

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