Newsela Staff on 10.27.16 Word Count 617

Hide and seek: Scientists look for planet some say is tilting solar system By Washington Post, adapted by Newsela staff on 10.27.16 Word Count 617

This artistic rendering shows the distant view from "Planet Nine" back toward the sun. The planet is thought to be gaseous, similar to Uranus and Neptune. Photo: Handout from Caltech/R. Hurt, IPAC

Astronomers, scientists who study space, can't see "Planet Nine." They don't know for sure if it exists. Now, though, they have more evidence that it is really out there.

Planet Nine is a massive mystery planet. Scientists say it is at the edge of the solar system. They say it weighs 5 to 10 times as much as Earth and takes 10,000 to 20,000 years to orbit the sun.

Konstantin Batygin and Mike Brown are the scientists who ﬁrst found evidence of Planet Nine. They teach at the California Institute of Technology. Now, with graduate student Elizabeth Bailey, they've found another clue. They think Planet Nine causes the tilt and "wobble" of our solar system.

Bailey led the new study. She said that the wobble is caused in part by Planet Nine's size. Because it is so big, it has an incredibly strong gravitational pull. Gravity is the force that pulls things together. Some Predictions Have Not Been True

No one knows for sure if Planet Nine is really out there. Batygin and Brown think it is there because of strange movements of the solar system. These movements could be caused by a huge planet far out in space. This is the same thinking that led scientists to discover the planet Neptune.

However, the history of astronomy is full of predictions that don't turn out to be true. The same person who discovered Neptune also predicted another planet, which he called Vulcan. He thought Vulcan was causing Mercury to wobble. Unfortunately, Vulcan didn't exist. Astronomers wasted years looking for it.

Batygin and Brown have collected convincing evidence of Planet Nine, though. They ﬁrst announced their ﬁnd in January. Planetary scientist Alessandro Morbidelli works at an observatory in France. When he heard their announcement, he said he was convinced that Planet Nine is out there.

"We will ﬁnd it one day," Morbidelli said. "The question is when."

Tilt Doesn't Make Sense

The newest evidence of Planet Nine has to do with how the planets in our solar system orbit, or circle, the sun. The planets all move around the sun in the same level. It's as if they are skaters on the same ice rink. Compared to the sun, though, this "rink" is at an angle. It's tilted about 6 degrees.

Scientists know a lot about how the solar system formed. This tilt doesn't make sense based on what they know. About 4.6 billion years ago, gravity started to pull together an enormous cloud of gas and dust. It made this cloud spin into a disk. The center collapsed into a hot, dense ball of gas. This became the sun. The rest gathered into planets. This suggests that the sun should be spinning on the same level as the planets, but it's not.

This is a big, important mystery, and it's very difﬁcult to explain, Brown says.

Planet Nine's Possible Effect

That's where Planet Nine comes in.

Planet Nine's orbit is even more tilted than the rest of the planets. The combination of its huge size and its tilt could have a big effect on the solar system. This could explain why the solar system tilts and wobbles. It might be responding to Planet Nine's massive gravity.

The new research offers another bit of proof for Planet Nine. It doesn't make it any easier for scientists to ﬁnd the planet, though. It also doesn't explain why Planet Nine is itself so tilted. The most important step will be actually ﬁnding Planet Nine. This won't be easy. The planet's orbit is very big and very far from Earth. Even using the most powerful telescopes to search the skies, it could be a very long wait to see Planet Nine. Quiz

1 Why do scientists think that Planet Nine is causing the solar system to wobble?

(A) because Planet Nine spins faster than the other planets

(B) because Planet Nine is a hot, dense ball of gas

(D) because Planet Nine has a huge amount of gravity

2 Which section of the article explains how the solar system was formed?

(A) Introduction [paragraphs 1-4]

(B) "Some Predictions Have Not Been True"

(D) "Planet Nine's Possible Effect"

3 Read the paragraph from the section "Some Predictions Have Not Been True."

What is the BEST deﬁnition of "predictions" based on the information in the paragraph?

(A) forecasts

(B) errors

(D) explanations 4 Read the sentence from the section "Some Predictions Have Not Been True."

Batygin and Brown have collected convincing evidence of Planet Nine, though.

What word could replace "convincing" WITHOUT changing its meaning?

(A) detailed

(B) massive

(D) thoughtful