Using ESA's Herschel space observatory, astronomers have
discovered vast comet belts surrounding two nearby planetary
systems known to host only Earth-to-Neptune-mass worlds. The
comet reservoirs could have delivered life-giving oceans to the
innermost planets. In a previous Herschel study, scientists
found that the dusty belt surrounding 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.
Herschel detected the signatures of cold dust at 200ºC below
freezing, in quantities that mean these systems must have at
least 10 times more comets than in our own Solar System's Kuiper
Belt. 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 'Goldilocks Zone' – the distance from the central
sun where liquid surface water could