Hunting Down Planet Nine (Planet X)

If Planet Nine really exists, astronomers have a pretty decent chance of spotting it.

On Wednesday (Jan. 20), scientists announced that a planet about 10 times more massive than Earth likely lurks in the distant outer solar system, orbiting perhaps 600 times farther from the sun than Earth does on average.

The evidence for the existence of this “Planet Nine” (ex-Planet X) is indirect at the moment; computer models suggest a big, undiscovered world has shaped the strange orbits of multiple objects in the Kuiper Belt, the ring of icy bodies beyond Neptune.

But direct evidence could come relatively soon, in the form of a telescope observation, Planet Nine’s proposers say.

“It’s actually not obscenely faint,” said Mike Brown of the California Institute of Technology (Caltech) in Pasadena. Brown and lead author Konstantin Batygin, also of Caltech, wrote the new paper laying out the evidence for the putative planet’s existence.

“In fact, it’s bright enough over a lot of its orbit that we should have seen it already, if it’s in the closest approaches to the sun,” Brown told Space.com.

Indeed, at closest approach,

“You could almost see it with some backyard telescopes,” he added.

(Planet Nine’s orbit likely brings it as close as 200 to 300 astronomical units, or AU, to the sun, and takes it as far away as 600 to 1,200 AU, Brown said. One AU is the average distance from Earth to the sun – about 93 million miles, or 150 million kilometers.)

Finding Planet Nine

Researchers say an anomaly in the orbits of distant Kuiper Belt objects
points to the existence of an unknown planet orbiting the sun.
Here’s what we know of this potential “Planet Nine.”
Credit: by Karl Tate, Infographics artist

Researchers say an anomaly in the orbits of distant Kuiper Belt objects

Points to the existence of an unknown planet orbiting the sun.

Here’s what we know of this potential “Planet Nine.”

Planet Nine is therefore probably not too close to the sun at the moment, said Brown, who has discovered or co-discovered a number of distant solar system objects, including the dwarf planets Eris and Sedna.

But powerful ground-based telescopes can probably still detect the object, wherever it may be, he added.

“Even at its most distant, and at the smallest guesses of how big it is, it’s like 24th or 25th magnitude,” Brown said, referring to the brightness scale astronomer’s use, in which higher numbers denote fainter objects.

“It’s not crazy; this is the kind of stuff people are finding all the time. We just need to go out and cover a good swathe of the sky.”

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