Wednesday, January 20, 2016

How Many Planets in our Solar System, do You Think?

"We have convincing evidence that the census of the solar system is incomplete.”

A huge planet might be sitting at the edge of our solar system without ever being seen.

The world — which could be about ten times as massive as Earth — would be large enough to become the ninth planet of our solar system.

The planet has not yet been seen by scientists. Instead, they have found it by watching the way that dwarf planets and other objects in the outer solar system move — their orbits seem to be disturbed by something huge but hidden sitting out there.

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“If there’s going to be another planet in the solar system, I think this is it,” Greg Laughlin of the University of California, Santa Cruz told National Geographic. “It would be quite extraordinary if we had one. Fingers crossed. It would be amazing.”

If the planet exists, it is thought to be about ten times as massive or three times as large as Earth. That sort of sized planet occurs throughout the universe — but has been an obvious omission from our own.

"This would be a real ninth planet," says Brown, the Richard and Barbara Rosenberg Professor of Planetary Astronomy. "There have only been two true planets discovered since ancient times, and this would be a third. It's a pretty substantial chunk of our solar system that's still out there to be found, which is pretty exciting."

It would be around 200 to 300 times as far away from the sun is when it gets closest to the star, scientists say. It will spend some of its time as much as four times as far away as that, and an entire orbit of the sun probably takes about 20,000 years.

The planet might have made its way out to the edge of the universe when it was thrown out there by the gravity of Jupiter or Saturn, the scientists suggest.

At such distances, the planet could be impossible to spot — even with the two huge telescopes that are currently looking for it. So little light is sent back from that far away, that it might never make it back for us to see.

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It is surrounded by much brighter lights — even the distant Pluto could be about 10,000 times brighter — and so scientists have to be sure that they point telescopes at exactly the right point and pick out an already very unlikely speck of light.

That is why the scientists have spotted the potential planet by seeing the disturbances that it is causing in the gravitational field of the far star system. There appears to be a “great perturber” upsetting the movement of other objects in that far away region, and the new paper — authored by Michael Brown and Konstantin Batygin and published in the Astronomical Journal — claims that is being caused by a mysterious, unknown world.

The solar system does not often change. The only recent addition was Pluto, which was found in 1930 and spent most of the 21st century as its most distant and smallest planet — until it was controversially downgraded to being just a dwarf planet, and the solar system went back to having eight members.

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If the new planet is real, then it will definitely be a planet, scientists say. Since it dominates a bigger region than any of the other planets, it would "the most planet-y of the planets in the whole solar system", Brown said.

The downgrading of Pluto was partly the result of work by astronomer Michael Brown, who co-wrote the new paper. He had found that Pluto was surrounded by a huge number of similarly sized planets, and the International Astronomical Union decided that Pluto would be excluded from a new definition.

The two astronomers found the new potential planet while they were looking at those small rocks. They seemed to fly around on orbits that could not be happening by chance, and instead were best explained by a big ninth planet sitting out there with them.

A ninth planet has long been hypothesized — and become the basis of some conspiracy theories — originally going under the name Planet X. It was first talked about more than a century ago, and looking for that planet was what brought astronomers to find Pluto.

The name of the planet will be crowd-sourced too, if the researchers get their way — as opposed to being proposed by the discoverer and then approved by the International Astronomical Union (IAU), which is the usual way of doing things. Brown’s and Batygin’s personal name preference is “George,” a hat-tip to British astronomer William Herschel, who discovered Uranus and wanted to name it Georgium Sidus (the Georgian Planet) after King George III. That might be a hard sell to the IAU—to say nothing of nearly all other stargazers, who tend to like a little more lyricism in their cosmos. “We actually call it Fatty when we’re just talking to each other,” Brown admitted.

Whatever the planet is eventually called, its very existence will do more than simply add to the population of the solar system. It will also add to its mystery. Even in our tiny corner of the universe, it seems, there can still be big surprises lurking.

Brown acknowledged that the history of astronomy is riddled with false hopes. Urbain Le Verrier, the French mathematician who correctly predicted the existence of Neptune, in 1846, also predicted the existence of a planet orbiting between the sun and Mercury. He called it Vulcan, and it turned out not to exist. Every few years, someone announces the discovery of Planet X, some large object that Galileo and four centuries of his descendants missed, only to retract it. “If somebody proposed this—if I picked up a newspaper and read a headline—my first reaction would be, Oh my God, these guys are crazy,” Brown said of his and Batygin’s finding. “But if somebody then looked at the evidence, they’d have a hard time disagreeing that the evidence is there.”

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