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| Space on Nov 28, 2012

Do missing Jupiters mean massive comet belt?

Two nearby planetary system have vast comet belts, but no Jupiter-like planets. Are those two things related?

Astronomers have discovered vast comet belts surrounding two nearby planetary systems known to host only Earth-to-Neptune-mass worlds, according to a November 27, 2012 ESA release. They determined that the systems – called GJ 581 and 61 Vir – must have at least 10 times more comets than in our own solar system’s Kuiper Belt.

The planets in both systems are known as ‘super-Earths’, covering a range of masses between two and 18 times that of Earth. Interestingly, however, there is no evidence for giant Jupiter- or Saturn-mass planets in either system.

Artist impression of the debris disc and planets around the star known as Gliese 581, superimposed on Herschel PACS images. The black oval outline sketched onto the Herschel data represents the innermost boundary of the debris disc; the approximate location of the outermost boundary is represented by the outer set of dashed lines. Image credit: ESA/AOES

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.

Dr. Mark Wyatt from the University of Cambridge is lead author of a paper focusing on the debris disc around 61 Vir. He said:

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.

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.

Dr. Jean-Francois Lestrade of the Observatoire de Paris led the work on GJ 581. He said:

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.

The astronomers used ESA’s Herschel space observatory for the new study

Bottom line: Astronomers have discovered vast comet belts surrounding two nearby planetary systems called GJ 581 and 61 Vir. They determined that the systems must have at least 10 times more comets than in our own solar system’s Kuiper Belt. The planets in both systems- are known as ‘super-Earths’, covering a range of masses between two and 18 times that of Earth. Interestingly, however, there is no evidence for giant Jupiter- or Saturn-mass planets in either system.

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