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Planetary smash-ups are bad news for alien life.

IT IS a dangerous universe out there. Astronomers have spotted the aftermath of an enormous collision between two distant planets, and their studies indicate that such violence could ruin the chances for life on planets that could otherwise be similar to Earth.
Almost 400 light years away, two nearly identical dwarf stars orbit one another. Around those stars sits a strange disc of dust.
That dust is far warmer than it ought to be, given that we would have expected it to have cooled in the past billion years since the star system formed.

Maggie Thompson at the University of California, Santa Cruz, and her colleagues suspect that a planetary calamity heated things up.
“The only thing that we could think of that could cause something like this is a recent collision between two planetary-sized bodies,” says Thompson.
the team doesn’t know when the collision took place, but suspect it was within the past 80,000 years.
These kinds of collisions probably happen all the time, particularly in systems with gas giants like Jupiter, according to Renata Frelikh at the University of California, Santa Cruz. Huge planets that orbit fairly close to their stars often have elongated orbits instead of circular ones. Looking at a sample of 311 planets, Frelikh and her colleagues have found that the planets with the most elongated paths tend to orbit a type of star that we know can produce lots of massive planets.
Her team’s simulations show that these strange orbits could be the signature of a period of planetary chaos in the systems’ history, where large worlds smashed into one another or gravitationally slingshotted each other away into space.
Despite these extreme systems being very different to our own, something similar probably happened here, says Frelikh.
“This phase might be a sort of common unifying feature in all planetary systems.”
If so, that might be a bad sign for alien life, she says.
“This violent phase might disrupt smaller planets, they might collide with the Jupiter-like planet or get thrown out of the system.”
To investigate how such instability would affect a smaller planet in the habitable zone around a star where surface water can remain liquid, Giorgi Kokaia at Lund University in Sweden and his colleagues ran simulations of 34 nearby planetary systems.
They found that, in most cases, the instability in the orbits of the giant planets would almostn definitely destroy any chances of life on the smaller worlds.
“The outer planets go unstable and send your habitable planet careening into the star, and that would not be very good for life on that planet,” says Kokaia.
Only seven of the 34 systems were likely to have planets that could stay in the habitable zone despite changes in the orbits of the giant planets. But for those that remain, a period of huge collisions and instability may be important. “These impacts can be really bad for planets and their habitability, but also sort of a blessing in disguise,” says Thompson.
On Earth, for example, a huge collision created the moon, which is important to life here, and impacts may also have brought water to the planet.
Studying these impacts not only helps us figure out where in the galaxy we should look for life, but also puts our own solar system in perspective.

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