An article (link to the file in PDF format) published in “The Astrophysical Journal Letters” reports a study on the circumplanetary disk around the exoplanet PDS 70 c. A team of researchers led by Myriam Benisty used the ALMA radio telescope to study what is still a protoplanet and the disk of materials around it that could form moons. According to estimates, there’s enough mass to form up to three moons the size of the Earth’s Moon. This type of study offers new information both on the formation of planets, especially gas giants, and on moons, one of the frontiers astronomers are trying to open.
The very young star PDS 70 has been under study for several years because there’s a planetary system still in its formation phase around it. Various instruments made it possible to study two gas giant protoplanets that were compared to the Jupiter-Saturn pair even though they’re already more massive than the two giants of the solar system. The protoplanets PDS 70 b and PDS 70 c haven’t yet completed their formation, so they’re particularly interesting for astronomers.
A further reason of interest came with a study published in “The Astrophysical Journal Letters” in July 2019 that reported the first results of observations conducted with the ALMA (Atacama Large Millimeter / submillimeter Array) radio telescope, inaugurated in March 2013. The researchers identified emissions from a possible circumplanetary disk that suggested the possible presence of moons in formation. That team, along with other researchers, continued observations with ALMA of the area around the protoplanet PDS 70 c.
This time, the results are considered unambiguous, confirming the presence of a circumplanetary disk from which moons could form. The image (ALMA (ESO/NAOJ/NRAO)/Benisty et al.) shows the PDS 70 system on the left with the detail of the protoplanet PDS 70 c with its circumplanetary disk on the right.
The observations conducted with the ALMA radio telescope are ideal because stars are very dim at millimeter and submillimeter wavelengths, so astronomers don’t have the problem of having to filter their light when studying protoplanetary disks around very young stars. For this reason, observations of the area around the protoplanet PDS 70 c have been going on for years with ALMA.
In recent years, several planetary systems have been discovered in the process of formation but PDS 70 at the moment seems the most interesting. The identification of two protoplanets and the subsequent discovery of traces of a circumplanetary disk around the PDS 70 c protoplanet may offer new insights into planetary and lunar formation processes. For example, the fact that there is no evidence of a similar disk around PDS 70 b suggests that gas and dust have been stolen from its neighbor.
A few thousand exoplanets have been identified so far but there are only a few exomoon candidates. This frontier represents a complex step in the study of other planetary systems because exomoons are much more difficult to detect than exoplanets. Having the first certainties about a potential moon nursery is interesting but it represents a single step forward in a type of research that will surely offer a lot of news in the coming years.
