The researchers used the ALMA observatory in Chile’s Atacama desert to detect the disc of swirling material accumulating around one of two newborn planets seen orbiting a young star called PDS 70, located a relatively close 370 light years from Earth. A light year is the distance light travels in a year, about 9.5 trillion km.
It is called a circumplanetary disc, and it is from these that moons are born. The discovery, they said, offers a deeper understanding about the formation of planets and moons.
More than 4,400 planets have been discovered outside the solar system, called exoplanets. No circumplanetary discs had been found until now because all the known exoplanets resided in “mature”, or fully developed, solar systems, except the two infant gas planets orbiting PDS 70.
“These observations are thus far unique. They have been long awaited to test the theory of planet formation, as well as to directly observe the birth of planets and of their satellites,” said astronomer Myriam Benisty of the University of Grenoble, who led the study published yesterday in the Astrophysical Journal Letters.
Planets ‘still in their youth’
In the solar system, the rings of Saturn, a planet around which more than 80 moons orbit, represent a relic of a primordial moon-forming disc, said study co-author Stefano Facchini of the European Southern Observatory.
The orange-colored star PDS 70, roughly the same mass as the sun, is about 5 million years old – a blink of the eye in cosmic time. The two planets are even younger, and it is around the one called PDS 70c that the disc has been observed.
Both planets are similar to Jupiter, although larger than it, and are “still in their youth”, Facchini said. They are at a dynamic stage in which they are still acquiring their atmospheres.
Stars burst to life within clouds of interstellar gas and dust scattered throughout galaxies. Leftover material spinning around a new star then coalesces into planets, and circumplanetary discs surrounding some planets similarly yield moons.
The disc around PDS 70c, with a diameter about equal to the distance of the Earth to the sun, possesses enough mass to produce up to three moons the size of Earth’s. It is unclear how many will form, if any.