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 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.
Interestingly, however, there is no evidence for giant Jupiter- or Saturn-mass planets in either system.
The gravitational interplay between Jupiter and Saturn in our own Solar System is thought to have been responsible for disrupting a once highly populated Kuiper Belt, sending a deluge of comets towards the inner planets in a cataclysmic 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," says 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," adds Dr Jean-Francois Lestrade of the Observatoire de Paris who led the work on GJ 581.
However, in order to produce the vast amount of dust seen by Herschel, collisions between the comets are needed, 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," says 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," says Göran Pilbratt, ESA's Herschel project scientist.
European Space Agency: http://www.esa.int
This press release was posted to serve as a topic for discussion. Please comment below. We try our best to only post press releases that are associated with peer reviewed scientific literature. Critical discussions of the research are appreciated. If you need help finding a link to the original article, please contact us on twitter or via e-mail.
NASA hopes Dawn mission can answer the big question: could life lurk in icy volcanoes on Ceres, the asteroid belt's biggest resident?
One twin will spend the year in space, the other on the ground. Monitoring their health could let us tease apart the effects of space flight from genetics
The Sierra Negra volcano in the central Mexican state of Puebla is the site of an ambitious astrophysical project which houses the largest gamma ray observatory ever built on the planet.
CAPE CANAVERAL, Fla (Reuters) - An unmanned Delta 4 rocket blasted off from Florida on Wednesday to deliver the ninth of 12 next-generation Global Positioning System satellites into orbit.
CAPE CANAVERAL, Fla (Reuters) - A NASA robot ship will pluck a large boulder off an asteroid and sling it around the moon, becoming an ad hoc destination to prepare for future human missions to Mars, the U.S. space agency said on Wednesday.
Scott Kelly and Mikhail Kornienko will spend a year together on the International Space Station and conduct research into the feasibility of a manned Mars mission
Jupiter may have ploughed through the early solar system, driving some of the first planets to a fiery death in the sun – and cleared room for planets like Earth
How did the Vikings find their way over the sea? Medieval artefacts are giving us important clues as to how they might have done it
New data clears up a case of mistaken stellar identity stretching back to the year 1670
But it wasn't exactly a fast race