Kepler Telescope Spots Tiniest Exoplanets Yet

At a meeting of the American Astronomical Society, scientists talked about mapping dark matter, measuring the 'graininess' of spacetime, and discovering the smallest exoplanets ever, using the Kepler space telescope. Ron Cowen, who reported on the meeting for Nature, discusses those findings.

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Welcome to SCIENCE FRIDAY. I am Ira Flatow. A few weeks ago, we talked about the discovery of new exoplanets, those planets outside of our solar system. There were the first Earth-sized exoplanets, and we had another exoplanet smack dab in the middle of the Goldilocks Zone, you know, where liquid water could exist. That was another first.

Well, the planet party continues because this week, astronomers announced the discovery of the smallest exoplanet so far, again with the Kepler Space Telescope. They presented those findings at a meeting of the American Astronomical Society in Austin.

My next guest has been reporting on the meeting all week. He's here to tell us a few bits of news about the universe. Ron Cowen is a freelance science Writer for Nature and Science, among others, and you can find links to his stories at the meeting at He joins us from NPR in Washington. Welcome back, Ron.

RON COWEN: Thanks, Ira.

FLATOW: Exciting stuff?

COWEN: Yeah, there's a lot of neat stuff. The exoplanet discovery, there's actually three new planets that - and they're all tinier than ever before, but the tiniest is about the size of Mars. All three of these guys orbit the same tiny dwarf star, and it's actually the most compact or miniature solar system we know about.

And none of these are in the Goldilocks Zone. They are all way too hot, too close to their parent star for liquid water to be there. But it's also interesting because all three of them are almost certainly rocky. They're tiny, so that they probably couldn't have held on to their atmosphere if they had one, but also they're so close to their parent star that the star would have - the heat from the star would have evaporated them.

So they're really rocky bodies, and now we can study rocky bodies, you know, similar in some ways to the ones in our own solar system.

FLATOW: So now that we're finding these things, we're figuring out there might be a lot of rocky planets out there.

COWEN: Well that's right because the interesting thing is that this - these bodies were found around red dwarf stars, these are stars half to one-sixth the size of the sun. They're the most common type of star in the Milky Way. About 80 percent of the stars in the Milky Way are red dwarfs.

And the thinking is that if we found a few around one red dwarf - and also Kepler doesn't mostly look at red dwarfs in the first place, it looks around sun-like stars mostly. If it's already found a system like this, the astronomers are saying that our Milky Way is teeming with rocky bodies, perhaps some of them in the Goldilocks Zone.

FLATOW: Let's talk about another story at the meeting, about mapping dark matter. I thought this was really interesting, too. The largest map of dark matter ever made, that right?

COWEN: That's right, that's right. Now dark matter, you know, is invisible. You can't see it. So you might think, well, you know, how can you map it? And it's sort of - if you - I'm going to go back to Goldilocks in a different way, Goldilocks and the three bears. I mean, if you're one of the three bears, and you didn't know Goldilocks was there, well, you saw your bed was broken, or you saw the porridge was eaten.

Well, dark matter, which makes up most of the mass in the universe but can't be seen, it has a gravitational tug. And according to Einstein, light from a distant object like a galaxy as it passes near one of these big, massive clumps of dark matter, will get bent, and the image will look distorted.

So they looked at images of 10 million galaxies across four different parts of the universe, and they statistically found a whole lot of distortions of these images. They could not account for these distortions by ordinary matter, there wasn't enough of it, so they therefore mapped the location of the dark matter, how they clump together.

This is important because we believe that dark matter is really what brought most of the visible mass together in the universe to form galaxies like the one we live in. So this is a way to make visible the invisible. It's also neat because dark matter is thought to be made of some exotic particles, we don't know what they're made of. The more we can at least map how they clump together and things like that is more of a clue to what they might be made of.

FLATOW: Does it tell us anything about that spooky dark energy stuff that's all out there?

COWEN: This is really just about dark matter. I mean, it has to fit into the overall rubric that dark matter is a certain percentage of the mass energy of the universe, but no, this is really, as I understand it, just about dark matter itself.

But it's the largest one, and it's also matching what the computer simulations that theorists have done for years. So they believe they're on the right track for how the universe formed and how galaxies formed.

FLATOW: That's always delightful when the actual facts match the theory, especially in physics.

COWEN: Yes. That's right, that's right. This is such exotic stuff.

FLATOW: There was one study that was looking at the nature of space-time, right?

COWEN: Right, right.

FLATOW: Tell us about that.

COWEN: So, yeah, and this is a little bit more complicated. So - and this has to do with gravity but in a different way. So the other forces of nature, like electromagnetism, like the force that holds protons and neutrons together in an atom, the so-called strong force and another type of force, they have all been united with quantum theory. But gravity has not.

And the other thing you should know is that, according to Einstein, gravity is actually a geometric theory, that we can replace the idea of gravity by just saying space-time is curved, and it's more curved where there's more gravity.

So some people think in order to unify gravity with quantum theory that space-time itself has to be quantized, it has to be grainy on some tiny, tiny scale. And if that's true, certain wavelengths of light, which are the highest - correspond to the highest energy photons of light, might bump into this graininess and might be slowed down by it, whereas photons of lower energy would not because they're longer wavelength, and it's like, I don't know, a bull in a china shop or something, you just - a big guy wouldn't see these tiny little grains.

So basically someone, actually several people, looked at what's called a gamma ray burst, which is a short-lived event, it's light generated by the explosion of a star, they looked at a high-energy photon and a low-energy photon and essentially it was erased. They knew or believed it was emitted at the same time, about 7 billion years ago.

And then they were detected by an Earth-orbiting telescope called Fermi, and you know what? This high-energy photon and the much lower energy one came - arrived - it was almost a dead heat, like within about a hundredth of a second of each other.

So according to this, that graininess, if it is there, did not disturb the light. Maybe graininess is the wrong idea, or maybe quantum gravity doesn't somehow become important to a smaller scale size, a smaller grain size than we might have thought.

And it's just - it's a beginning of a way to get at this. You know, when I talk about graininess, this is like a trillionth of a trillionth the size of a hydrogen atom. I'm talking really small. And it's kind of amazing that this cosmic race across halfway of the universe can start, start to say something about this stuff.

FLATOW: So theory wins one today, and theory loses one today.

COWEN: That might be possible, yes, yes.


FLATOW: As I think Steven Weinberg once said: Physics doesn't care what scientists want.


COWEN: That's right, that's right.


FLATOW: Thank you, Ron.

COWEN: Thank you.

FLATOW: Take care. Thanks for being with us today. Ron Cowen is a freelance science writer for Nature and Science, among others, and you can find links to his stories from that meeting there at


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