ESA Spots Massive Comet Belts Surrounding Two Planetary Systems

 Vast comet belts have been noticed surrounding two nearby star planetary systems. These belts were observed using European Space Agency's Herschel Space Observatory.

According to the astronomers who discovered the belts, the comet reservoirs could have delivered life giving oceans to the innermost planet.

In a previous Herschel study, scientists found that the dusty belt surrounding nearby star Fomalhaut must be maintained by collisions between comets.

Two more nearby planetary systems have been found in the new Herschel study; namely GJ 581 and 61 Vir. These two have been found to host vast amounts of cometary debris.

The signature of cold dust was detected by Herschel at 200 degree C below freezing point. The quantity in which it was detected indicated these systems must have at least 10 times more comets than in our own Solar System's Kuiper Belt.

Known to be the low mass M dwarf, star GJ 581 or Gliese 581 is the most common type of star in the galaxy.

Prior to this, studies have indicated that it hosts at least four planets, including one that resides in the 'Goldilocks Zone'.   This zone refers to the distance from the central sun where liquid surface water could exist.

Two planets are confirmed around G-type star 61 Vir, which is just a little less massive than our Sun. The planets in both systems are known as 'super-Earths', covering a range of masses between 2 and 18 times that of Earth. However, there has been no evidence for giant Jupiter- or Saturn-mass planets in either system.

Till date the reason for the disruption of the highly populated Kuiper Belt was thought to be the gravitational interplay between Jupiter and Saturn in our own Solar System. They sent a flood of comets in the direction of the inner planets in a disastrous event that lasted several million years.

"The new observations are giving us a clue: they're saying that in the Solar System we have giant planets and a relatively sparse Kuiper Belt, but systems with only low-mass planets often have much denser Kuiper belts," said Dr Mark Wyatt from the University of Cambridge, lead author of the paper focusing on the debris disc around 61 Vir.

"We think that may be because the absence of a Jupiter in the low-mass planet systems allows them to avoid a dramatic heavy bombardment event, and instead experience a gradual rain of comets over billions of years."

"For an older star like GJ 581, which is at least two billion years old, enough time has elapsed for such a gradual rain of comets to deliver a sizable amount of water to the innermost planets, which is of particular importance for the planet residing in the star's habitable zone," added Dr Jean-Francois Lestrade of the Observatoire de Paris who led the work on GJ 581.

Collisions between the comets are needed in order to produce the vast amount of dust seen by Herschel, which could be triggered by a Neptune-sized planet residing close to the disc.

"Simulations show us that the known close-in planets in each of these systems cannot do the job, but a similarly-sized planet located much further from the star -- currently beyond the reach of current detection campaigns -- would be able to stir the disc to make it dusty and observable," said Dr Lestrade.

Herschel is finding a correlation between the presence of massive debris discs and planetary systems with no Jupiter-class planets, which offers a clue to our understanding of how planetary systems form and evolve," said Göran Pilbratt, ESA's Herschel project scientist.