Astronomers Discover Mysterious Exoplanet; No One Can Figure Out How It Formed
An international team of astronomers have discovered a planet unlike any other. It's big and relatively new; it even has some of its birth dust still circling around it, a "debris disk" in astronomy jargon. Bailey's exoplanet, as it is being called, is only 13 million years old — compared with earth's 4.5 billion years — so it's still just a baby. Even so, researchers have no idea how it formed. "No model of either planet or star formation fully explains what we see," said Vanessa Bailey, a graduate student who led in the research (and for whom the planet is named), in a statement.
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The most puzzling part is how far it is away from its star: about 60 billion miles, or 650 times the average distance of the earth to the sun. That means the planet (official name: H 106906 b) is too distant from its sun to have been formed like the planets in our solar system, through collisions of rock and dust. That process is too slow to make a giant planet so far away. H 106906 b is 11 times the mass of Jupiter. Another theory: A giant planet could theoretically form from the swift collapse of material. But that also couldn't happen so far away; there wouldn't be enough mass. The discovery "throws a wrench in planet formation theories," said the University of Arizona, where Bailey conducted the study. The paper has been accepted for publication in The Astrophysical Journal Letters.
They've got several other hypotheses, but none of them work. One interesting proposal suggests that the planet was almost going to be a second star, forming a "binary star" system. In those situations, two stars catch in the other's orbit and swing around each other like kids spinning while holding hands. Scientists proposed that maybe this planet couldn't muster enough material to combust into a star. "It is possible that in the case of the H 106906 system the star and planet collapsed independently from clumps of gas, but for some reason the planet's progenitor clump was starved for material and never grew large enough to ignite and become a star," Bailey said.
But no, it's probably not that, either. Bailey says the ratio of binary star masses usually isn't greater than 10-to-1. In this case, it's more like 100-to-1. "This extreme mass ratio is not predicted from binary star formation theories — just like planet formation theory predicts that we cannot form planets so far from the host star," Bailey said. And so HD 106906 b remains a freak planet. "Every new directly detected planet pushes our understanding of how and where planets can form," said co-investigator Tiffany Meshkat, a graduate student at Leiden Observatory in the Netherlands. She said discoveries like this help color our understaning of solar systems other than our own.
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