美国国家公共电台 NPR Astronomers Are On A Celestial Treasure Hunt. The Prize? Planet Nine（在线收听）

Astronomers Are On A Celestial Treasure Hunt. The Prize? Planet Nine

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Astronomers now think they've discovered a new planet in our solar system. All they have to do is find it. NPR science correspondent Joe Palca has been exploring scientists' passion for discovery as part of his series Joe's Big Idea. Today he brings us a story of a celestial treasure hunt to find Planet Nine.

JOE PALCA, BYLINE: Nobody's actually seen the new planet. The reason astronomers think it's out there is the strange behavior of some smallish objects orbiting in the outer reaches of the solar system. By studying the so-called extreme Kuiper Belt objects, astronomers have deduced that the gravity of something big, something ten times more massive than the Earth, seems to be tugging on them, altering their paths around the sun. Caltech astronomer Mike Brown says it's hard to know exactly where that tug is coming from.

MIKE BROWN: We don't have complete orbits of any of our objects yet. So if you could wait 15,000 years, I could pinpoint exactly where Planet Nine is.

PALCA: For now, all Brown can do is map out a swath of sky where his computer model says the new planet might be. And that's one of the problems with Brown's predictions for the new planet. They're based on just a handful of small objects. And some astronomers are skeptical there's enough evidence to make a credible treasure map. Brown's Caltech colleague Konstantin Batygin says they were aware that invoking a new planet to explain the strange behavior of their objects would expose them to ridicule. There have been a lot of wild goose chases in the search for new planets.

KONSTANTIN BATYGIN: We worked hard for about a year to try and find some other explanation.

BROWN: Because we were kind of tired of everybody always saying, there must be a planet. There must be a planet. There must be a planet, even - we were tired of ourselves having said it several times.

PALCA: When did it go from, oh, that's ridiculous to, wait a minute, maybe that's not ridiculous?

BROWN: So that was at a - there was a moment when that happened.

PALCA: Brown says the moment came because of something unexpected their computer model predicted. The model said not only would a giant planet explain the behavior of distant objects, such a planet would also tilt the orbits of some objects closer to the sun by 90 degrees. And did such objects exist? One day, Brown found an astronomical survey that appeared to have them.

BATYGIN: We went over to Mike's office. And...

BROWN: I had the predictions from the computer model on. And I put the new objects on top of the predictions, and they sat exactly where they were supposed to sit.

BATYGIN: It was this moment where you sit back, and you recognize that this is actually real.

BROWN: Not just this cute little math anymore.

BATYGIN: For the first time, we actually believe ourselves. This planet is really out there.

PALCA: Batygin and Brown aren't the only ones convinced there's something to look for. Scott Sheppard is an astronomer at the Carnegie Institution for Science in Washington, D.C. He was the first to notice the strange behavior of the distant objects and suggest a new planet might be responsible. Like Brown and Batygin, he expects the new planet to be in an orbit much, much farther out than Neptune. But he expects it may be visible later this year, and he'll be using large telescopes to search the most promising patches of sky.

SCOTT SHEPPARD: We're both aware that this big object could be out there. We're both interested in very similar science. We're not teaming up, but we also don't want to compete against each other. So what we have agreed to do is share our field. So if we observe a certain area of sky, there's no reason for anyone else to observe that sky again.

PALCA: There's an interesting dynamic here. On the one hand, Sheppard would like someone to find the planet because it would vindicate the predictions that it's out there.

SHEPPARD: Of course - yeah, you just want to find it. And anyone would want it to be them, for sure. But it would be nice just to find it, just to know that what we're seeing out there is real.

PALCA: Caltech's Mike Brown says he feels the same way.

BROWN: We want it found. I would rather that somebody finds it tomorrow than that we find it in 10 years. I'd rather I find it tomorrow, I mean, to be honest.

PALCA: It would be oddly fitting if Brown did find the new planet since he had a major role in demoting Pluto from planetary status a decade ago. Right now, Brown says finding the planet is basically a matter of luck. You happen to pick the right patch of sky, you win. We may know who got lucky by the end of the year - or maybe not. Joe Palca, NPR News.