Astronomers exploring the disk of debris around the young star Beta Pictoris have discovered a compact cloud of carbon monoxide located about 8 billion miles (13 billion kilometers) from the star. This concentration of poisonous gas - usually destroyed by starlight - is being constantly replenished by ongoing rapid-fire collisions among a swarm of icy, comet-like bodies.

In fact, to offset the destruction of carbon monoxide (CO) molecules around the star, a large comet must be getting completely destroyed every five minutes, say researchers.

They suggest the comet swarm is most likely frozen debris trapped and concentrated by the gravity of an as-yet-unseen exoplanet.

This mystery 'shepherd' exoplanet - so-called for its capacity to corral the swarms of comets through its gravitational pull, like Jupiter in our own solar system - is likely to be about the size of Saturn.

"Detailed dynamical studies are now under way, but at the moment we think this shepherding planet would be around Saturn's mass and positioned near the inner edge of the CO belt," said Mark Wyatt, from Cambridge's Institute of Astronomy, who proposed the shepherd model - currently the favoured hypothesis because it explains so many puzzling features of the Beta Pictoris disk.

"We think the Beta Pictoris comet swarms formed when the hypothetical planet migrated outward, sweeping icy bodies into resonant orbits."

Paradoxically, the presence of carbon monoxide - so harmful to humans on Earth - could indicate that the Beta Pictoris planetary system may eventually be a good habitat for life. If there is CO in the comets, then there is likely also water ice - meaning that the cometary bombardment this system's planets are probably undergoing could also be providing them with life-giving water.

The clump was discovered when an international team of astronomers, led by ALMA-based ESO astronomer Bill Dent, along with Wyatt, used the Atacama Large Millimeter/submillimeter Array (ALMA) in Chile to map the millimeter-wavelength light from dust and carbon monoxide molecules in the disk surrounding Beta Pictoris, a star located about 63 light-years away and only 20 million years old.

Beta Pictoris is considered one of the best examples of a typical young solar system, and hosts one of the closest and brightest debris disks known - making it an ideal laboratory for studying the early development of planetary systems. The latest findings could help us understand what conditions were like during the formation of our own solar system.

Much of the carbon monoxide is concentrated in a single clump located about 8 billion miles (13 billion kilometers) from the star, or nearly three times the distance between the planet Neptune and the sun. The total amount of the gas observed exceeds 200 million billion tons - equivalent to about one-sixth the mass of Earth's oceans, say researchers.

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Galactic gas caused by colliding comets suggests mystery 'shepherd' exoplanet