For the first time, scientists were able to confidently see the dust disk around an extrasolar planet using the ALMA antenna array in the Chilean highlands. These observations shed light on the formation mechanisms of planets and moons in young stellar systems.
“The result of our work is a clear registration of the disk in which satellites of the planet can form,” says Myriam Benisty, researcher at the University of Grenoble in France and head of the work. were able to confidently identify the disk associated with the planet and estimate its size, "she adds.
The results of the study were published on July 22 in the scientific journal The Astrophysical Journal Letters.
How and why the moon was formed - a satellite of the Earth - scientists only speculate. There are almost a dozen hypotheses on this topic. And most of them consider the Moon as a detached solid piece of something, pulled by the Earth's gravity into its orbit.
The recently discovered "moon-forming" disk around the exoplanet is seen by scientists as a real proof of a different process of origin of satellites of large planets.
The so-called near-planetary disk surrounds the exoplanet PDS 70c - one of two giant planets like Jupiter. These two planets revolve around a star that is nearly 400 light-years away.
Astronomers have previously found signs of the existence of a "moon-forming" disk around this exoplanet. But since it was not possible to clearly distinguish the disk from its environment, it was not possible to confidently confirm the existence of the disk. Now there is confidence in this - the disc exists.
Benisti and her group used ALMA to find out that the diameter of the disk is approximately equal to the distance from the Earth to the Sun, and its mass would be enough to form three satellites the size of the Moon.
"These new observations are critical to testing planetary theories that have so far been impossible to test," said Jaehan Bae of the US Carnegie Institute for Research.
Planets form in dusty disks around young stars, pulling material from the circumstellar disk toward them. Voids are formed in the disk. In this case, the planet can form its own - circumstellar - disk, which affects the process of the planet's growth, regulating the amount of circumstellar matter falling on it.
Gas and dust in the circumplanetary disk in the course of multiple collisions can concentrate in ever larger bodies, which ultimately leads to the birth of the planet's satellites - moons.
According to ESO researcher Stefano Facchini, astronomers are not yet fully clear on all the details of these processes - "when, where and how planets and their satellites are formed."
"To date, more than 4,000 exoplanets have been discovered, but all of them are in already mature planetary systems. PDS 70b and PDS 70c, which are similar to the Jupiter-Saturn pair, remain the only exoplanets recorded that are still in the process of formation," says Miriam Keppler (Miriam Keppler), employee of the Max Planck Institute for Astronomy in Germany, one of the co-authors of the work.
PDS 70b and PDS 70c - the two planets that make up this planetary system - were discovered with ESO's Very Large Telescope (VLT) in 2018 and 2019, respectively. Due to their uniqueness, they have since been observed many times with different telescopes and antennas.
"It turns out that this system provides us with a unique opportunity to observe and study the formation of planets and their satellites," sums up Facchini.
The current high-resolution observations at ALMA have given astronomers a better understanding of the system's features. As a result, not only was the presence of a near-planetary disk around PDS 70c confirmed, its dimensions and mass were studied, but also the absence of clear evidence of the existence of the same disk around PDS 70b was found. It seems that the planet PDS 70c pulled all the dust from the parent cloud around PDS 70b and left the sister planet without moons.