Conditions in the early universe might have enabled rocky planets with water to form much earlier than anticipated, potentially allowing life to begin sooner too.
Astrophysicists studying the early universe think planet formation didn’t begin in earnest until supernovae had released enough heavy elements to form planetesimals, the building blocks of rocky planets, around stars. Our sun and its planets arose when the universe was about 9 billion years old, and the oldest known planet developed into the life of the universe.
at the University of Portsmouth, UK, and his colleagues suggest planet formation could have taken place much earlier, just 200 million years after the big bang and before some of the first galaxies started to form.
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According to their modelling, planets could have formed around stars smaller than our sun, born from the remains of powerful early supernovae called pair-instability supernovae. These explosions, involving stars hundreds of times the mass of the sun that were the first to form in the universe, could have released enough heavy elements to form planets, the researchers found.
This would have included large amounts of oxygen, which means the discs around the resulting stars could also have contained a considerable amount of water, almost comparable in quantity to the amount of water in our solar system.
“Habitable worlds thus formed among the first generation of stars in the universe, before the advent of the first galaxies,” the researchers say in a paper reporting their findings. Whalen declined to speak to żěè¶ĚĘÓƵ while the paper is under submission with a journal.
at the Open University, UK, says that if planetesimals were able to form so early in the universe, then there is “no reason to expect there were not any planets”. However, their habitability could depend on the presence of gas giants, which might be crucial for limiting the amount of impacts on rocky planets that could render them uninhabitable, as well as for shepherding water-bearing asteroids and comets to such worlds, she says.
“I don’t think giant planets could form in that environment” so early in the universe, says Barstow. “I just don’t think there’s enough material.” Whether rocky planets this early in the universe could retain atmospheres, given expected flares and activity from nearby stars, is another open question.
at the University of Cambridge says we might be able to test the idea that planets formed so early by looking for ancient planets orbiting stars today with low amounts of heavy elements, similar to low-mass stars in the early universe. “Seeing evidence of such planet formation would be a really cool thing,” he says. “That would really spur modelling to understand how planet formation can occur in more challenging circumstances.”
Actually seeing any planets around stars in the first 200 million years of the universe would be much more difficult, and require telescopes much more powerful than the ones in operation today. But the idea is “definitely interesting and deserves further investigation”, says Barstow.
arXiv
