Study reveals that giant planets could reach "maturity" much earlier than previously thought

An international collaboration between scientists of the Istituto Nazionale di Astrofisica (INAF) and the Instituto de Astrofísica de Canarias (IAC), together with other institutions from Spain, Germany, Belgium, UK, and Mexico, has been able to measure the masses of the giant planets of the V1298 Tau system, just 20 million year old. For this result they have used radial velocity measurements from the HARPS-N spectrographs, at the Telescopio Nazionale Galileo, Roque de los Muchachos Observatory (ORM), and CARMENES, at the Calar Alto Observatory. Masses for such young giant planets had not been obtained previously, and this is the first evidence that these objects can reach their final size with a quick evolution. The results are published in the journal Nature Astronomy.

The study, led by the IAC researcher Alejandro Suárez Mascareño, reports the measurement of the masses of two giant planets, b and e, that orbit the young solar-type star V1298 Tau. They were discovered in 2019 using data from NASA's Kepler space telescope, which allowed the measurement of their sizes, slightly smaller than Jupiter.

The characterization of very young planets is extraordinarily difficult. The parent stars have very high levels of activity and until very recently it was unthinkable to even try. In fact, for the new measurements of the planetary masses, it was necessary to separate the signals generated by these planets from the signal generated by the star's activity, almost ten times larger.

This system was considered very interesting since its discovery, and we included it in a long-term observation program carried on by the team of the Global Architecture of Planetary Systems (GAPS) collaboration. Only thanks to the combination of photometric data already available, with new measurements of the stellar radial velocity from Earth-based observatories and the use of the most advanced analysis techniques, we are starting to understand what is happening in such early stages of the evolution of V1298 Tau and its planets.

The study shows that the masses and radii of the planets V1298 Tau b and e are both surprisingly similar to those of the giant planets of the Solar System or in other old extra-solar systems. These measurements, which are the first to be obtained of such young giant planets, allow us to test current ideas about the formation of planetary systems. For many years, theoretical models have indicated that giant planets begin their evolution as bodies with a large size, and later they contract over hundreds millions or even billions of years. We now know that they can actually reach a size similar to that of the planets in the Solar System in a very short time.

The study of young systems gives researchers clues about what happened during the infancy of our solar system. We still do not know if V1298 Tau is a normal or an exceptional case; if this were the normal scenario, it would mean that the evolution of planets like Jupiter and Saturn could have been very different from what we think. There are two more smaller and internal planets in this system, and our observation campaign continues, in order to characterize all of them. The next step is understanding whether these planets are affected by mild or rapid evaporation, given the large irradiation from their parent star.

To achieve the measurement of these masses, the study has required a significant observational effort and the collaboration of multiple observatories and institutions from different countries. Among the contributors, there are twelve italian researchers from Torino, Padova, Roma, and Palermo. Beside the data obtained with HARPS-N@TNG, it has been necessary to gather radial velocity measurements from the CARMENES high resolution spectrograph, installed at the Calar Alto observatory, the HERMES spectrograph at the Mercator telescope, also at the ORM, and the SES spectrograph at the STELLA telescope of the Teide Observatory. Observations taken from the Las Cumbres Observatory, a network of telescopes located around the world, have been used to continuously monitor the variations of the star's activity.

Image/Video credit: Gabriel Pérez Díaz, SMM (IAC)

Article: Rapid contraction of giant planets orbiting the 20 million-years old star V1298 Tau – DOI: 10.1038/s41550-021-01533-7