First asteroid belts discovered in Vega system, points to exoplanets

Signs of two large asteroid belts around Vega, which is the second brightest star in northern night skies, were reportedly found by astronomers employing the two infrared space telescopes Herschel from the European Space Agency, and Spitzer from NASA.

It would be just the second asteroid belt system identified outside of our own solar system, with the other located in the Fomalhaut system. Both stars appear to have inner, warm belts and outer, cool belts separated by a gap - a similar setup to the asteroid and Kuiper belts in our own solar system.

And since this kind of setup in our own solar system is only possible due to the smaller planets in the inner system, and the large planets between the inner and outer asteroid belts, it is quite likely that there are similar planetary systems around those two stars too - or are in the process of forming, since the stars are much younger than the sun.

"Our findings echo recent results showing multiple-planet systems are common beyond our sun," says Kate Su, an astronomer at the Steward Observatory at the University of Arizona.

Both Vega and Fomalhaut are about twice the mass of our sun and burn a hotter, bluer color in visible light. Both are about 25 light-years away and are thought to be around 400 million years old for Fomalhaut, and 600 million years for Vega, which is rather young compared to the 5 billion year old sun. One giant planet was already discovered in the outer of both systems, Fomalhaut b, which appears to be in a very eccentric 2000-year orbit around the star though.

To find the asteroid belts, the Herschel and Spitzer telescopes detected infrared light emitted by the warm and cold dust in separate bands. The dust is constantly formed by colliding chunks of rock in the belts, and fast comets crashing into it.

Both the inner and outer belts contain far more material than our own asteroid and Kuiper belts, which could be on one hand because the star systems are far younger than our own, and also since the system likely formed from an initially more massive cloud of gas and dust.

The proportion of the gap between the inner and outer debris belts for both Vega and Fomalhaut also corresponds to the distance between our sun's asteroid and Kuiper belts, with the outer belt 10 times farther away from its host star than the inner belt.

The large gap between the two indicates for astronomers that there are several undetected planets, Jupiter-sized or smaller, creating a dust-free zone between the two belts by sweeping up debris.

"Overall, the large gap between the warm and the cold belts is a signpost that points to multiple planets likely orbiting around Vega and Fomalhaut," says Su.

"Upcoming new facilities such as NASA's James Webb Space Telescope should be able to find the planets," said paper co-author Karl Stapelfeldt, chief of the Exoplanets and Stellar Astrophysics Laboratory at NASA's Goddard Space Flight Center in Greenbelt, Md.