Elusive Planet Nine causes sun’s curious tilt, scientists say

Planet 9
© Caltech/R. Hurt (IPAC)

The presence of the huge and distant (and as-of-yet unseen) planet explains many enduring mysteries; now a study suggests it’s responsible for the unusual tilt of the sun.

From the "so many things we have to learn about our planet and its solar system" department.

We seem to think we know things for a fact, but then, well, we don’t. The world isn’t flat, the sun doesn’t revolve Earth, and now … maybe there’s another planet in our solar system that has yet to be seen.

Move over Pluto, not only were you demoted, but based on the predictions by Caltech's Konstantin Batygin and Mike Brown earlier this year, there may be an official ninth planet to take your place.

The presence of a ninth planet, known as Planet Nine, would answer many questions that have stumped scientists for a long time. The latest puzzle piece to fall into place is how it explains the unusual tilt of the sun, according the astronmers who say it may be adding a wobble to the solar system, giving the appearance that the sun is tilted slightly.

"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," says Elizabeth Bailey, a graduate student at Caltech and lead author of a study announcing the discovery.

The planets in our solar system all orbit in a flat plane relative to the sun, but the plane itself rotates at a six-degree tilt with respect to the sun, making the sun appear to have a jaunty angle – up to now nobody has known why.

"It's such a deep-rooted mystery and so difficult to explain that people just don't talk about it," says Brown, the Richard and Barbara Rosenberg Professor of Planetary Astronomy.

But Brown and Batygin's suggestion of Planet Nine – which is 10 times the size of Earth – would change the physics of the goings-on out there in the wild blue yonder. Going by their calculations, the elusive planet seems to orbit at about 30 degrees off from the other planets' orbital plane, which alters the orbit of a large number of things in the Kuiper Belt, which is how the team came to first suspect another planet might be at play.

"It continues to amaze us; every time we look carefully we continue to find that Planet Nine explains something about the solar system that had long been a mystery," says Batygin, an assistant professor of planetary science.

That Planet Nine helps to explain the tilt of the solar system's orbital plane is another vote of confidence for the planet’s existence. The tilt has long confounded astronomers because of the way the planets formed: as a spinning cloud slowly collapsing first into a disk and then into objects orbiting a central star, according to Caltech (who can say this better than I can):

Planet Nine's angular momentum is having an outsized impact on the solar system based on its location and size. A planet's angular momentum equals the mass of an object multiplied by its distance from the sun, and corresponds with the force that the planet exerts on the overall system's spin. Because the other planets in the solar system all exist along a flat plane, their angular momentum works to keep the whole disk spinning smoothly.

Planet Nine's unusual orbit, however, adds a multi-billion-year wobble to that system. Mathematically, given the hypothesized size and distance of Planet Nine, a six-degree tilt fits perfectly, Brown says.

In this video the scientists talk about the latest discovery, it's so interesting.

Why Planet Nine has such an unusual orbit is the next question – well after the main question, of course: where is it? But as for the tilt, Batygin suggests that the planet may have been kicked out of the gas giants' neighborhood by Jupiter, or may have been pulled by other stellar bodies in the solar system's distant past.

Regardless, for now the new research adds fuel to the excitement as the team and their colleagues continue their search for signs of Planet Nine. See more about this elusive giant in the video below.

Elusive Planet Nine causes sun’s curious tilt, scientists say
The presence of the huge and distant (and as-of-yet unseen) planet explains many enduring mysteries; now a study suggests it’s responsible for the unusual tilt of the sun.

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