Things aren鈥檛 looking so good for Planet Nine. Astronomers have been seeking signs of a purported giant planet in the outer reaches of our solar system since 2014, but new observations hint that it may not actually be there.
In 2014, astronomers noticed that rocks in the outer solar system called extreme trans-Neptunian objects, or eTNOs, seemed to be inexplicably clumped together. That clumping, along with their strange elongated orbits, could possibly be explained by the gravitational influence of a planet with five to 10 times the mass of Earth.
But new data brings into question whether eTNOs are clumped at all. Pedro Bernardinelli at the University of Pennsylvania and his colleagues analysed data from the Dark Energy Survey (DES) on seven eTNOs and found no evidence for any unexpected clumping 鈥� so no reason to dream up a new planet. 鈥淲e would not have formulated the Planet Nine idea if our data was the only data that existed,鈥� says Bernardinelli.
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鈥淎s we鈥檙e finding more of these distant objects, the distribution starts to look more even,鈥� says Samantha Lawler at the University of Regina in Canada. 鈥淚t鈥檚 pretty bad for the idea of Planet Nine.鈥�
That may be because the eTNO data used in the original Planet Nine analysis came from several different observatories, without considering whether they covered a random sample of the sky. There is no way to know now whether the objects they saw were actually clustered in one direction, or whether the observatories just happened to look in that direction more than any other, says Lawler.
This new analysis isn鈥檛 enough to prove that Planet Nine doesn鈥檛 exist. 鈥淭he way that the Planet Nine hypothesis is constructed is that it鈥檚 completely impossible to falsify it 鈥� the only way to prove it鈥檚 not there is to search every square centimetre of the sky and not find it,鈥� says Lawler.
鈥淭hese results don鈥檛 worry me too much,鈥� says Mike Brown at the California Institute of Technology, who was one of the formulators of the Planet Nine hypothesis and leads a team looking for it. All the data we have on eTNOs, when viewed together, still points to the possibility of a ninth planet, he says.
We need to find many more eTNOs to get close to a definitive answer, but their elongated orbits, which take them extremely far from the sun, make them tough to spot. If we eventually find that they aren鈥檛 clumped up and there is no evidence for Planet Nine, these unusual orbits are hard to explain.
鈥淓ven if they鈥檙e not clustered, we still have to explain how they got there,鈥� says Bernardinelli.
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