Cold debris: An artist's impression of an icy planet orbiting an alien star.
Credit: European Southern Observatory
SYDNEY: New observations from NASA's Spitzer Space Telescope suggest that icy planets are common around young, bright stars.
U.S. researchers say they have found evidence of icy planets – ranging in size from smaller than Pluto to as big as Neptune – around half of all 'A-type' stars in a nearby star cluster, called NGC 2232.
A-type stars are about twice as massive and twice as hot as the Sun.
"Like car crashes"
The researchers used data from NASA's Spitzer Space Telescope and the ROSAT All-Sky Survey (a now defunct international satellite X-ray observatory) to observe A- and B-type stars that dwell 25 million light-years away in the constellation Monoceros, a faint group of stars between the Orion and Gemini constellations.
As they detail this week in the Astrophysical Journal, the researchers found one star ringed with a warm dusty disk where rocky planets might form, and 12 stars which had cold, dusty disks which they claim is made from the debris of icy planet-forming collisions.
"Planets grow by accreting small, kilometre-sized objects via collisions. Like car crashes, these collisions produce debris," said lead author, U.S. astrophysicist Thayne Currie from the Harvard-Smithsonian Centre for Astrophysics in Cambridge, Massachusetts.
Nascent planets
This debris emits energy gained by absorbing radiation from the star. The wavelengths of the emissions indicate the temperature of the dust and how far away it is from the star.
Armed with this knowledge and using models of how planets form, the researchers interpreted their data to see what kind of planetary collisions might produce the observed debris.
The results predicted that young stars, around 25 million years old, and slightly more massive than the Sun, would likely have dozens of 1000-kilometre-sized nascent planets.
"Basically, we have very solid evidence that icy planets with sizes on the order of 1,000 km or greater are there, but we cannot say with confidence [how big they are]" Currie told Cosmos Online.
