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Time: 2016-10-21 05:26:13 UTC

Original URL: https://www.washingtonpost.com/news/speaking-of-science/wp/2016/10/20/the-mysterious-planet-nine-might-be-causing-the-whole-solar-system-to-wobble/ [washingtonpost.com] using UTF-8 encoding.

Title: The mysterious 'Planet Nine' might be causing the whole solar system to wobble

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The mysterious 'Planet Nine' might be causing the whole solar system to wobble

Arthur T Knackerbracket has found the following story [washingtonpost.com]:

The massive hypothetical object [washingtonpost.com], which supposedly looms at the edge of our solar system, has been invoked to explain the strange clustering of objects in the Kuiper belt and the unusual way they orbit the Sun.

Now Planet Nine predictors [washingtonpost.com] Konstantin Batygin and Mike Brown of Caltech, along with graduate student Elizabeth Bailey, offer another piece of evidence for the elusive sphere's existence: It adds "wobble" to the solar system, they say, tilting it in relation to the sun.

"Because Planet Nine is so massive and has an orbit tilted compared to the other planets, the solar system has no choice but to slowly twist out of alignment," lead author Bailey said in a statement.

Before we go any further, a caveat about Planet Nine: It's purely theoretical at this point. Batygin and Brown predict its existence [washingtonpost.com] based on unusual perturbations of the solar system that aren't otherwise easily explained. (This is the same technique scientists used to find Neptune.) But the history of astronomy is rife with speculation that is never borne out: The same guy who correctly predicted the existence of Neptune also believed that a planet he called Vulcan was responsible for the wobble of Mercury. That "discovery" caused the astronomy world to waste years looking for something that wasn't there. (Mercury's wobble was eventually explained by the theory of general relativity.)

But the evidence offered by Batygin and Brown is compelling. When the pair announced their find in January, planetary scientist Alessandro Morbidelli [wikipedia.org] of the Côte d'Azur Observatory in Nice, France, told The Washington Post: "I don't see any alternative explanation to that offered by Batygin and Brown."

"We will find it one day," he added. "The question is when."

The new research led by Bailey is based on the observation that the sun rotates on a different axis than the orbits of the planets. Mercury, Venus, Earth, Mars, Jupiter, Saturn, Uranus and Neptune all move around the sun in a flat, shared plane — it's as if the planets were skaters on the same rink. But that plane is tilted at a six-degree angle with respect to the sun (which, from our perspective, makes it look like the sun is tilted).

This tilt doesn't jibe with how astronomers say the solar system formed: 4.6 billion years ago, gravity started to pull together a vast, scattered cloud of gas and dust, causing it to spin into a disk. The center of the circle collapsed into a hot, dense ball of gas — the sun — and the remainder accumulated into planets. Because the sun came from the same disk as everything else, it should be spinning on the same plane. But it's not.

"It's such a deep-rooted mystery and so difficult to explain that people just don't talk about it," Brown said.

Enter Planet Nine. Based on Batygin and Brown's previous calculations, the hypothesized planet weighs five to 10 times as much as Earth and is, on average, 20 times farther from the sun than Neptune. It takes Planet Nine 10,000 to 20,000 years to orbit the sun.

Planet Nine also orbits at an even more dramatic angle than the rest of the planets: about 30 degrees. That fact, combined with its distant location and massive size, could mean that its angular momentum puts the rest of the solar system off-kilter.

"It's an argument that is basically like an asymmetrical seesaw or a dolly," Batygin told Astronomy Magazine [astronomy.com]. "Planet Nine has a really long orbit, so it can assert quite a bit of torque on the inner planets without having to apply so much force. Planet Nine has as much angular momentum as the entire solar system combined, because its orbit is so big."

Over the course of several billion years, that could be enough to explain the six-degree tilt we now see.

Original Submission