Newly Discovered Planet Challenges Astronomers' Notions Of How Planets Form A surprisingly large planet orbiting a small star defies the conventional wisdom about how planets are born. But a dark-horse idea from more than 20 years ago could explain it.

A Peculiar Solar System Has Scientists Rethinking Theories Of How Planets Form

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Scientists have detected thousands of planets outside our solar system in recent years. They've found everything from gas giants to smaller, Earth-sized worlds. NPR's Nell Greenfieldboyce reports they have now found a planet that challenges the conventional wisdom about how planets form.

NELL GREENFIELDBOYCE, BYLINE: This newly discovered planet orbits a tiny, dim red star about 30 light-years away from Earth. Juan Carlos Morales is an astrophysicist at the Institute of Space Studies of Catalonia in Barcelona. He and his colleagues used a telescope to watch the star. They saw a telltale wobble that meant it was being tugged by the gravity of a big planet.

JUAN CARLOS MORALES: In terms of size, it's - it may be very similar to Jupiter.

GREENFIELDBOYCE: That was a surprise.

MORALES: It's a very large planet for such a small star.

GREENFIELDBOYCE: So large that it defies the most popular explanation for how planets form.

Alan Boss is an astronomer at the Carnegie Institution for Science in Washington, D.C. He explains that newborn stars are temporarily surrounded by a swirling disc of leftover gas and dust.

ALAN BOSS: Those dust grains are what form the cores of the giant planets, as well as the bulk of the terrestrial planets, like Earth.

GREENFIELDBOYCE: The little bits of solid material collide and stick together, gradually building up and getting larger and larger - like, over a million years or more. At least, that's how scientists have explained all the planets they've found until now. Boss says, around this puny star, that process would happen too slowly to form a gas giant before the disc of gas and dust disappeared.

So what did create this planet? Well, in the journal Science, researchers say there's another possibility, one Boss first proposed way back in 1997. Part of the star's disc could spontaneously contract and collapse into a planet.

BOSS: So that can happen in something like a hundred years.

GREENFIELDBOYCE: Boss says this idea hasn't been taken all that seriously. I asked him how he felt about scientists finally finding a planet that can only be explained in this way.

BOSS: (Laughter) Well, I still - a little shocked that someone actually thinks that I've got - my ideas have some merit. So I am sure I'll get over it, but it's very pleasant.

GREENFIELDBOYCE: Sara Seager is a planetary scientist at MIT. She likes this discovery because it's the latest example of how, in science, there's frequently two competing explanations.

SARA SEAGER: And in the end of the day, it often turns out that both paradigms or both concepts are right, actually.

GREENFIELDBOYCE: She says nature is smarter than we are. If humans can imagine something, it's likely that the universe has done it.

Nell Greenfieldboyce, NPR News.

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