Astronomers have discovered a disc surrounding the star HD 115600 that provides the closest match to what the solar system may have looked like early in its evolution. The discovery will allow us to put our theories of the evolution of comets on firmer ground.
HD 115600 is 1.4-1.5 times as massive than the sun, but close enough to be a good model. Moreover, at 360 light-years away in Centaurus, it is relatively easy to observe—at least for Southern Hemisphere telescopes. HD 115600 is at a very early stage in its development, just 10-20 million years old, and is part of the Scorpius-Centaurus OB association, a group of stars that formed together.
A planet-forming disc lies 37-55 astronomical units (AU) from the star, a location very similar to the 30-50 AU of the Kuiper Belt—the region from which many comets originate. The Kuiper Belt also contains such objects as Pluto, Charon and Eris. The blue-gray color is consistent with the chemicals that dominate the Kuiper Belt.
The disk sits slightly off-kilter relative to the star, which Dr. Thayne Currie of Hawaii's Subaru Observatory attributes to the likely presence of unseen planets. The disc's shape suggests the presence of a giant planet, either one with a mass similar to Neptune just inside the ring, or something larger than Jupiter inside 30 AU. Currie and his co-authors suggest that such objects may be detectable with very large telescopes.
"It's almost like looking at the outer solar system when it was a toddler," said Currie, who praised the power of the new Gemini Planet Imager. "In just one of our many 50-second exposures we could see what previous instruments failed to see in more than 50 minutes.”
Proto-planetary disks have been seen around other stars, including a neighbor of HD 115600, but have generally been closer to the star or revealed a different stage of evolution.