美国国家公共电台 NPR A Friend For Pluto: Astronomers Find New Dwarf Planet In Our Solar System（在线收听）

A Friend For Pluto: Astronomers Find New Dwarf Planet In Our Solar System 

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Scientists in Michigan have found a new dwarf planet in our solar system. The way it was found is quite unusual, and the researchers hope their technique will help in the search for an even more impressive object - a giant planet astronomers believe is lurking in the outer reaches of our solar system. NPR's Joe Palca has this story about the big idea that may lead to finding what astronomers are calling Planet Nine.

JOE PALCA, BYLINE: Some researchers have devoted their lives to finding new objects in the solar system - not David Gerdes.

DAVID GERDES: I came to planet hunting not only - not as a planet hunter, but I'm actually an adult-onset astronomer.

PALCA: Gerdes started out as a particle physicist. Then he turned to cosmology and got involved in an effort to make a map of distant galaxies. This has involved taking tens of thousands of pictures of the night sky. A couple years ago, Gerdes had some undergraduates visiting him for the summer, and he said to them, just for fun, let's see if we can find some solar system objects in our images. So how do you find solar system objects in pictures taken of the sky looking for galaxies? Well, you look for things that move.

GERDES: Objects in the solar system, when you observe them at one instant and then a little while later, they appear to be in a different place in the sky.

PALCA: Stars and galaxies are so far away they're basically stationary. But a planet or asteroid will be in a slightly different position from night to night. It will appear as a dot of light that seems to be moving across the stationary backdrop of stars. Connect the dots night after night and you can begin to calculate the object's orbit around the sun. But the images Gerdes had weren't taken night after night.

GERDES: We often just have a single observation of the thing on one night, and then two weeks later, one observation and then five nights later, another observation, and four months later, another observation. So the connecting-the-dots problem is much more challenging.

PALCA: But they were able to develop software that can do just that. I met with Gerdes and some of his student collaborators in a conference room on the University of Michigan campus last month. He told me about one of the more interesting objects they've fished out of their images - a new dwarf planet that's really, really far away, nearly 100 times farther from the sun than the Earth is. And it takes more than a thousand years to complete a single orbit.

GERDES: We think this object could be about a thousand kilometers in diameter - not Pluto-sized but still one of the larger minor bodies in the solar system.

PALCA: Since we spoke last month, Gerdes now has additional data showing the object is closer to 500 kilometers in diameter, but that's still a big chunk of rock. Now, this new dwarf planet is pretty exciting if you're into dwarf planets, but there's a much bigger prize astronomers are searching for. They think there's a planet ten times more massive than the Earth hiding in the outer reaches of the solar system. A scientific paper earlier this year described the orbit of this so-called Planet Nine, and since then, astronomers have been scouring the parts of the sky where the orbit says Planet Nine might be. So far, no one's seen it. David Gerdes says it's quite possible that one of the images taken for his galaxy map may actually contain a picture of it.

GERDES: I'm excited about our chances of finding it.

PALCA: When you say our, you mean yours or you mean our as in us planet Earth people?

GERDES: I'm excited about the chances of the people in this room finding it. Of course, I'm happy for humanity if someone else finds it. It would be the most exciting astronomical discovery in our lifetime I think.

PALCA: No luck so far, but as David Gerdes says...

GERDES: The hunt is on.

PALCA: Joe Palca, NPR News.