Oldest known planet-forming disk discovered

Scientists have discovered the oldest known planet-forming disk - a 45 million-year-old ring of gas and dust that orbits around a young star, from which planets can form as the material collides and aggregates.

Led by Steven Silverberg of the University of Oklahoma, the team described a newly identified red dwarf star with a warm circumstellar disk, of the kind associated with young planetary systems.

Circumstellar disks around red dwarfs like this one are rare to begin with, but this star, called AWI0005x3s, appears to have sustained its disk for an exceptionally long time.

"Most disks of this kind fade away in less than 30 million years," said Silverberg.

"This particular red dwarf is a candidate member of the Carina stellar association, which would make it around 45 million years old. It's the oldest red dwarf system with a disk we've seen in one of these associations," he said.

The discovery relied on citizen scientists from Disk Detective, a project designed to find new circumstellar disks.

At the project's website, users make classifications by viewing ten-second videos of data from NASA surveys, including the Wide-field Infrared Survey Explorer mission (WISE) and Two-Micron All Sky Survey (2MASS) projects.

Since the launch of the website in January 2014, roughly 30,000 citizen scientists have participated in this process, performing roughly 2 million classifications of celestial objects.

"Without the help of the citizen scientists examining these objects and finding the good ones, we might never have spotted this object," said Marc Kuchner, from NASA's Goddard Space Flight Centre.

"The WISE mission alone found 747 million (warm infrared) objects, of which we expect a few thousand to be circumstellar disks," Kuchner said.

Determining the age of a star can be tricky or impossible.

But the Carina association, where this red dwarf was found, is a group of stars whose motions through the Galaxy indicate that they were all born at roughly the same time in the same stellar nursery.

Researchers devised a test that showed this newly found red dwarf and its disk are likely part of the Carina association, which was key to revealing its surprising age.

"It is surprising to see a circumstellar disk around a star that may be 45 million years old, because we normally expect these disks to dissipate within a few million years," said Jonathan Gagne, from Carnegie Institution for Science in the US.

The star and its disk may the possibly host extrasolar planets, researchers said. Most of the extrasolar planets that have been found by telescopes have been located in disks similar to the one around this unusual red dwarf.

Moreover, this particular star is the same spectral type as Proxima Centauri, the Sun's nearest neighbour, which was shown to host at least one exoplanet - Proxima b.

The findings were published in The Astrophysical Journal Letters.