November 27, 2012
Astronomers Discover Comets Scattered Throughout Planetary Systems
Lee Rannals for redOrbit.com — Your Universe OnlineGJ 581 and 61 Vir, have been found to host vast amounts of cometary debris.
The ESA observatory detected the signatures of cold dust 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 is a low-mass M dwarf star, which is the most common type of star in the galaxy. Previous studies have shown that it hosts at least four planets, including one that resides in the "Goldilocks Zone," which is the distance needed for a planet to have liquid water on its surface.
Both systems contain "super-Earths," which cover a range of masses between 2 and 18 times that of Earth. So far, no evidence has shown that there is a giant Jupiter or Saturn-mass planet in either system.
In our Solar System, scientists believe gravitational interplay between Jupiter and Saturn have been responsible for disrupting a once highly populated Kuiper Belt.
“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,” Dr Mark Wyatt from the University of Cambridge said in a statement.
“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,” he added.
Dr Jean-Francois, Lestrade of the Observatoire de Paris who led the work on GJ 581, said for an older star like GJ 581, enough time has elapsed for a gradual rain of comets to deliver a sizable amount of water to the innermost planets.
In order to produce the vast amount of dust seen by Herschel, collisions between the comets are needed.
“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,” Dr Lestrade said.
GÃ¶ran Pilbratt, ESA´s Herschel project scientist, said that Herschel is helping to find a correlation between the presence of massive debris discs and planetary systems with no Jupiter-class planets. He added that this offers a clue to scientists' understanding of how planetary systems form and evolve.