Scientists at Caltech claim to have found further evidence indicating the existence of a ninth planet in the Solar System. They also believe that the planet, if it really exists, will be discovered within the next decade.
The idea of 'planet nine' has floated about within the scientific community for a while. It started with the discovery of some distant objects lurking beyond Neptune, exhibiting some strange orbits.
In 2016, Caltech's Konstantin Batygin and Mike Brown presented the first evidence that a massive planet could be present in the outer Solar System and orbiting the Sun in a weird, highly elongated orbit. It was also suggested that this unknown planet - dubbed planet nine - could be influencing the motion of other objects in the outer Solar System.
In June 2016, Batygin and Brown followed up with further details about hypothetical planet, including observational constraints on the location of the planet along its orbit.
While the existence of planet nine was proposed about three years ago, scientists haven't got any success so far in spotting the planet.
Batygin and Brown have now published two papers analysing the evidence for planet nine's existence.
In one paper, published in journal Physics Reports, researchers used new computer models to estimate the hypothetical physical properties of planet nine. The analysis suggested that this planet likely lies somewhat closer to the Sun than previously thought.
The planet is smaller and has mass about five times that of Earth. Earlier, scientists had estimated that it could be about 10 times more massive than Earth.
New estimates also suggest that planet nine is likely located about 400 astronomical units (about 60 billion kilometres) away from the Sun. One astronomical unit equals the distance of the Earth from the Sun (about 149.6 million kilometres).
The reason why astronomers have failed to spot planet nine so far is that it is a faint object, and scientists really don't know where to point their telescopes in the sky to find the planet.
However, they are hopeful that the planet, if it really exists, will be found within the next 10 years.
"My favourite characteristic of the planet nine hypothesis is that it is observationally testable," says Konstantin Batygin, an assistant professor of planetary sciences at CalTech and co-author of the second paper.
"The prospect of one day seeing real images of planet nine is absolutely electrifying. Although finding planet nine astronomically is a great challenge, I'm very optimistic that we will image it within the next decade."
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