ALMA reveals a disk forming the moon around a distant planet

By using the most powerful network of radio telescopes on earth, astronomers have made the first observations of a circumplanetary disk of gas and dust similar to that which would have given birth to the moons of Jupiter.

The discovery, reported today online in Astrophysical Journal Letters, adds to the intriguing story of the planet PDS 70c, a gas giant in formation about 370 light-years from Earth that was revealed for the first time last month in visible light images.

Using the very large Atacama Large Millimeter / submillimeter Array network with 66 antennas (ALMA) in Chile, astronomer Andrea Isella of Rice University collected millimeter-wave radio signals revealing the presence of dust particles throughout the star system where PDS 70c and its sister planet, PDS 70b, are formed always.

"The planets form from gas and dust disks around newly formed stars.If a planet is large enough, it can form its own disk when it collects materials around the planet. star, "said Isella. "Jupiter and its moons are a small planetary system in our solar system, for example, and it is thought that the moons of Jupiter were formed from a circumplanetary disk while Jupiter was very young."

But most of the planet's formation patterns show that the circumplanetary disks disappear after about 10 million years, which means that circumplanetary disks have not existed in our solar system for more than 4 billion years. To search for them elsewhere and gather evidence to test the theories of planet formation, Isella and her colleagues are looking for very early star systems where they can directly observe the discs and planets that are still forming at the planet. 39; inside. In the new study, Isella and her colleagues analyzed the observations made by ALMA in 2017.

"There are a handful of candidate planets that have been detected in the discs, but it's a whole new field, and they're all still being debated," Isella said. . "(PDS 70b and PDS 70c) are among the most robust because there have been independent observations with different instruments and techniques."

PDS 70 is a dwarf star representing about three quarters of the mass of the sun. Its two planets are 5 to 10 times larger than Jupiter, and the deepest, PDS 70b, is orbiting about 1.8 billion kilometers from the star, about the distance from the sun to Uranus. The PDS 70c is one billion kilometers away, in an orbit the size of Neptune.

PDS 70b was first revealed in 2018 in infrared light images of a planet search instrument called SPHERE at the Very Large Telescope (VLT) of the European Southern Observatory. In June, astronomers used another VLT instrument called MUSE observe a wavelength of visible light called H-alpha, which is emitted when the hydrogen falls on a star or planet and becomes ionized.

"H-alpha gives us more confidence in the fact that they are planets, because it suggests that they always suck up gas and dust and that they grow up," Isella said.

The millimeter wave length observations provided by ALMA provide even more evidence.

"It's complementary to the optical data and provides a totally independent confirmation that there is something out there," he said.

According to Isella, direct observation of planets with circumplanetary disks could allow astronomers to test theories of planet formation.

"There are a lot of things we do not understand about planet formation, and we finally have the tools to make direct observations and start answering questions about the formation of our solar system and the formation of solar systems. other planets. "

Isella is Assistant Professor of Physics and Astronomy and Earth Sciences, Environment and Planets at Rice, and Co-Investigator of the CLEVER Planets project, funded by NASA and based at Rice.

Co-authors of the study include Myriam Benisty of the University of Chile and the University of Grenoble Alpes, Richard Teague of the University of Michigan, Jaehan Bae of the Carnegie Institution for Science, Miriam Keppler of the Max Planck Institute for Astronomy, Stefano Facchini of the European Southern Observatory and Laura Pérez of the University of Chile.

The research was funded by the National Science Fund, the French National Research Agency, NASA, the Chilean National Commission for Scientific and Technological Research, the National Fund of Chile for Scientific and Technological Development, European Union Horizon 2020 and the European Southern Observatory.