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Did two planets around nearby star collide? Toxic gas holds hints

Astronomy and Astrophysics
Gas clouds near Beta Pictoris could be remnants of a collision between two Mars-sized planets.
A more likely scenario, researchers say, is that comets are smashing into each other once every 5 minutes.
Though the carbon monoxide clouds would be poisonous to humans, they may hint at life in that solar system.

In a young, nearby solar system, scientists have discovered giant clouds of poison gas -- the smoking gun from a violent encounter, astronomers say. Based on massive amounts of carbon monoxide gas around the star Beta Pictoris, either two Mars-sized planets slammed into each other with catastrophic results, or hordes of comets are crashing into one another at an astounding rate.

The findings, published by the journal Science, could help provide an up-close look at how stars and their planetary systems form and evolve.

Beta Pictoris lies about 63 light years away and is only about 20 million years old. It has at least one planet, a gas giant that’s several times Jupiter’s mass and sits roughly nine times as far from its home star as Earth sits from our sun. It also has a dusty disc of debris circling the star -- the detritus from collisions between its inhabitants. 

"Many stars are surrounded by disks of dusty debris formed in the collisions of asteroids, comets and dwarf planets," the study authors wrote. "But is gas also released in such events?"

Astronomers can't directly see the debris from these dramatic but distant smash-ups, but any gassy trails left over could provide them with evidence of their aftermath.

Because the star’s disc is so young and nearby (by astronomical standards), and because our solar system is more than 4.5 billion years old, watching Beta Pictoris’ evolution lets us see what a developing planetary system might look like.

Astronomers using the Atacama Large Millimeter/submillimeter Array, or ALMA, telescope were able to pick out a strange clump of carbon monoxide gas in the star’s debris disc. These random clouds of gas lie far out -- about 8 billion miles from the star, or roughly three times the distance from Neptune to our sun. What’s strange is that they really shouldn’t stick around long -- after all, starlight causes carbon monoxide to break down within about 100 years. So unless astronomers have caught the Beta Pictoris system at a very awkward stage in its life -- an unlikely scenario -- the gas clump must be getting refills from somewhere.

The researchers think this could be caused by a traffic jam of comets, held in thrall by the gravitational influence of a gas giant planet. To produce the massive amounts of gas -- more than 200 million billion tons -- the comets would have to be smashing together at a rate of once every five minutes. In our own solar system, massive Jupiter’s gravitational pull disrupted a field of debris and kept it from forming into a planet, leaving us with the asteroid belt.

The researchers think a massive gas giant planet far out in the system could be having a similar effect. The gas giant Beta Pictoris B, a mere 750 million miles from its star, is probably not the culprit, though it could be if the planet started much farther out in its system -- closer to the distant, theorized comet cloud -- and then migrated inward over time.

It’s also possible that these massive amounts of gas could be the result of two icy, Mars-sized bodies smashing into each other, the authors said.

In a strange twist, even though carbon monoxide is poisonous to humans, the toxic clouds could be a sign that this nearby star hosts worlds that are friendly to life: The comets that may be raining down on any planets in Beta Pictoris would also be bringing carbon- and oxygen-rich organic molecules to the surface of these planets.

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