Astronomers have discovered vast comet belts surrounding two nearby planetary systems known to host planets.

Astronomers have discovered vast comet belts surrounding two nearby planetary systems known to host planets. These cometary belts could have delivered oceans to the innermost planets. The findings are based on observations from the Herschel space telescope, a European Space Agency mission with participation from NASA.

Last year, Herschel found that the dusty belt surrounding the nearby star Fomalhaut must be maintained by collisions between comets.

In the new Herschel study, two more nearby planetary systems - GJ 581 and 61 Vir - have been found to host vast amounts of cometary debris.

The artist's impression above shows the orbits of planets and comets around 61 Vir, superimposed on a view from Herschel.

GJ 581 (or Gliese 581) is a low-mass M dwarf star, the most common type of star in the galaxy. Earlier studies have shown that it hosts at least four planets, including one that resides in the so-called habitable zone - the region from the central sun where liquid surface water could exist.

For more on the discovery, see the NASA press release.