An article published in the journal “Astronomy & Astrophysics” reports evidence of the existence of a planet in formation in the protoplanetary disk surrounding the young star AB Aurigae. A team of researchers led by Anthony Boccaletti, of the Observatoire de Paris, PSL University, France, used the SPHERE instrument mounted on ESO’s VLT in Chile to find traces of what could be a planet. SPHERE takes real photos of the objects, so if the discovery was confirmed it would be the first direct evidence of a planet seen while it’s forming.

About 520 light-years from Earth, AB Aurigae is a star that, with an estimated age of 3-4 million years, is still so young that it hasn’t yet entered the main sequence, the stable phase in which a star spends most of its life. For this reason it’s been the subject of studies for years, including the protoplanetary disk that surrounds it. The ALMA radio telescope made it possible to identify spiral arms and the possible traces of a planet in formation, reported in an article published in May 2017 in “The Astrophysical Journal”.

Now this new research has exploited the SPHERE (Spectro-Polarimetric High-contrast Exoplanet REsearch) instrument, activated in June 2014 to search for exoplanets. Mounted on ESO’s VLT (Very Large Telescope), it’s generally used to directly photograph exoplanets that are already formed, but there are occasions when it can be used in a slightly different way, in this case, to photograph a possible planet that is still forming inside of AB Aurigae’s protoplanetary disk.

The image (ESO/Boccaletti et al.) shows on the left the photo of the AB Aurigae system captured by the SPHERE instrument, and on the right a zoomed image of the protoplanetary disk’s inner part with what appears to be a planet in formation in the bright yellow zone.

When there’s a planetary formation in progress, the gas is pushed by the object in formation generating disturbances in the disk in the form of a wave, which Emmanuel Di Folco of the Bordeaux Astrophysical Laboratory (LAB), France, one of the authors of the study, compared to the wave from a boat on a lake. As the planet orbits its star, this wave takes the form of a spiral arm. The region in which a sort of bright yellow twist is seen near the center of AB Aurigae’s image shows precisely this type of disturbance at a distance from the star which is more or less that of Neptune from the Sun.

Anne Dutrey, also from LAB and one of the authors of the study, added that that bright yellow twist corresponds to the connection between two spirals, one winding inwards of the planet’s orbit, and the other that is expanding outwards. They allow gas and dust from the disk to accrete on the planet in formation to make it grow.

This study is based on direct photos of the AB Aurigae system, not on electromagnetic waves captured by a radio telescope to then reconstruct an image. This means that this could be the first direct evidence of a planet in formation. Further observations will be conducted because it becomes more important than ever to confirm this result and try to get some estimate on that protoplanet’s mass. All of that will also help to better understand the process of planetary formation.