A "dust trap" surrounding a young star could help explain how planets are formed, astronomers with Chile's ALMA space observatory said on Thursday.

The findings provide insight into how dust particles in the disk around a young star grow in size so that, over time, they form comets and planets.

"It's likely that we are looking at a kind of comet factory," said Nienke van der Marel, a doctoral student at Leiden University in the Netherlands, who led the team of researchers.

Van der Marel and her co-workers made their discovery when they used the ALMA observatory to study the disc in a system called Oph-IRS 48.

They discovered that the star was circled by a ring of gas with a central hole, but what surprised them was the view of where larger, millimeter-sized dust particles were found, said a release from the European Southern Observatory that co-funds ALMA.

"Instead of the ring we had expected to see, we found a very clear cashew-nut shape," Van der Marel said. "We had to convince ourselves that this feature was real, but the strong signal and sharpness of the ALMA observations left no doubt about the structure."

What they had come across was a so-called dust trap -- a place where larger dust grains were trapped and could grow in size by colliding and sticking together.

Van der Marel noted that the conditions in the "comet factory" were right for the particles to grow from millimeter to comet size, but not to planet size.

"But in the near future, ALMA will be able to observe dust traps closer to their parent stars, where the same mechanisms are at work," she said. "Such dust traps really would be the cradles for newborn planets."

The ALMA space observatory was inaugurated on a Chilean desert plateau in March and the findings were published in the June 7 issue of the Journal Science.

ALMA -- short for the Atacama Large Millimeter-submillimeter Array, an acronym which means "soul" in Spanish -- is a joint effort among North American, European and Asian agencies.

Unlike optical or infrared telescopes, ALMA can capture the faint glow and gas present in the formation of the first stars, galaxies and planets in an extremely cold region of the universe.