Disk "forming the moon" found in a distant star system

US astronomers have reported the earliest observations of a circumplanetary disk, the belt of dust and gas that, according to theory, controls the formation of planets and gives rise to a complete system of moons, such as those found around Jupiter.

Atacama's Large Atomimeter / Millimeter (ALMA) network was observed around one of the planets of PDS 70, a young star about 370 light-years from Earth.

Recently, astronomers have confirmed the presence of two massive planets, Jupiter type. The very large telescope (VLT) of the European Southern Observatory has detected the warm glow naturally emitted by the hydrogen accumulated on the planets.

The new ALMA observations instead reflect the weak radio waves emitted by the tiny dust particles (about a tenth of a millimeter) around the star.

Combined with previous optical and infrared observations of the VLT, they provide irrefutable evidence that a dusty disc capable of forming multiple moons surrounds the outermost known planet of the system, astronomers write in an article to appear in the journal. Astrophysical Journal, Letters and currently available on the pre-print server arXiv.

"For the first time, we can conclusively see the telltale signs of a circumplanetary disk, which helps support many of the current theories about planet formation," said lead author Andrea Isella, of Rice University in Houston.

"By comparing our observations to high-resolution infrared and optical images, we can clearly see that an otherwise enigmatic concentration of tiny dust particles is actually a dust disk that surrounds the planet, the first characteristic of this type ever observed. conclusively. "

Unlike the icy rings of Saturn, which have probably formed recently during the crushing of comets and rocky bodies in the history of our solar system, a circumplanetary disk is the persistent trace of the process of planet formation.

Astronomers explain that optical studies of planetary systems are a major challenge because the star is so much brighter than planets that it is difficult to filter reflections.

However, ALMA observations do not have this limit because stars emit relatively little light at millimeter and submillimetre wavelengths.

"This means we can return to this system at different times and better map the orbit of the planets and the concentration of dust in the system," says Isella.

"This will give us unique insights into the orbital properties of solar systems in their very early stages of development."