IT IS a dangerous universe out聽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 Astrophysical Journal, ).
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鈥淭he only thing that we could聽think of that could cause聽something like this is a recent collision between two planetary-sized bodies,鈥� says Thompson. The team doesn鈥檛 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聽type of star that we know can produce lots of massive planets.
Her team鈥檚 simulations show聽that these strange orbits could be the signature of a period of planetary chaos in the聽systems鈥� history, where large聽worlds smashed into one聽another or gravitationally slingshotted each other away into space (The聽Astrophysical Journal Letters, ).
Despite these extreme systems being very different to聽our own, something similar probably happened here, says Frelikh. 鈥淭his phase might be a聽sort of common unifying feature in all planetary systems.鈥�
If so, that might be a bad sign聽for alien life, she says. 鈥淭his聽violent phase might disrupt smaller planets, they聽might collide with the Jupiter-like planet or get thrown聽out of the system.鈥�
To investigate how such instability would affect a smaller planet in the habitable zone around a star where surface water can remain liquid,聽Giorgi Kokaia at Lund University in Sweden and his colleagues ran simulations of 34聽nearby planetary systems. They found that, in most cases, the instability in the orbits of the giant planets would almost definitely destroy any chances of life on the smaller worlds. 鈥淭he 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,鈥� 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聽the giant planets (). But for those that remain, a period of huge collisions and instability may be聽important. 鈥淭hese impacts can be really bad for planets and聽their habitability, but also sort of a blessing in disguise,鈥� 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.
