The protoplanetary disk AS 209 hides at least one planet

The protoplanetary disk AS 209 (Image ALMA (ESO/NAOJ/NRAO)/ D. Fedele et al.)
The protoplanetary disk AS 209 (Image ALMA (ESO/NAOJ/NRAO)/ D. Fedele et al.)

An article published in the journal “Astronomy & Astrophysics” describes the study of the protoplanetary disk AS 209. A team of researchers led by Davide Fedele of INAF Arcetri, Italy, used the ALMA radio telescope to observe that disk of gas and dust around a star in its formation phase showing a central core and two large rings with two large gaps. Their conclusion is that there’s at least one planet with a mass that could be close to Saturn’s orbiting at a considerable distance from its star.

About 410 light years away from the Earth, the AS 209 system is of the T Tauri type, meaning that the star at its center is of the pre-main-sequence type, a protostar still in the course of its formation phase in which the accretion process is still in progress. In this phase, it emits energy due to its gravitational collapse and not because of hydrogen fusion.

The ALMA radio telescope (Atacama Large Millimeter/submillimeter Array), inaugurated in March 2013, is allowing to capture details never seen from a number of protoplanetary disks and to see their evolution underway. The AS 209 system, in the Ophiuchus star formation region, contains one of them.

The materials that form these disks are slowly coalescing to form planets and other smaller celestial bodies and in this case the signs are seen in the gaps already present in the disk. The study of those features can provide information on the status of the processes underway in that system to better understand how it’s evolving.

The large outer gap is deep, wide, and contains little dust, evidence of the presence of a planet that could be a gas giant with a mass around two thirds of Saturn’s. Its distance from its star is remarkable, more than three times that of Saturn from the Sun. The action it performs on the protoplanetary disk causes an accumulation of dust on its orbit’s outer edge and this creates well-defined rings in the disk.

The thinner internal gap may have been created by another smaller planet, but the researchers also suggested the hypothesis that the outer planet generated both gaps. Regardless of the actual situation, the presence of the outer planet raises some questions about the formation of planets at a great distance from their star. In this case, this happened on the outer edge of the protoplanetary disk in a time that’s probably short from the astronomical point of view since the system is still in the process of formation.

The researchers suggested some possibilities regarding gas and dust movements to explain the formation of the planet but there are no certainties. It’s for these reasons that it’s important to continue to study the various known protoplanetary disks: each of them is a different case and can provide new information on the processes of star systems formation.

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