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LINDA WERTHEIMER, host:

Welcome back to ALL THINGS CONSIDERED from NPR News. I'm Linda Wertheimer. This month, NASA's Kepler Mission announced it had found 54 planets orbiting stars in so-called habitable zones in our galaxy. Then the SETI Institute, the organization that searches for extraterrestrial intelligence, turned its radio telescopes toward those 54 planets listening for signs of life.

Nothing yet, but as reporter Brent Baughman says, intelligent life is not the only thing that makes noise in space.

(Soundbite of star)

BRENT BAUGHMAN: This is the sound of a star. And it's true that in space, no one can hear you scream, but this sound didn't travel through space as a sound. It traveled as wave energy, just like my voice is reaching your radio.

Mr. JON JENKINS (NASA Researcher): This particular one is Kepler ID 7671081.

BAUGHMAN: NASA researcher Jon Jenkins created this recording just like your radio might: by transforming wave energy, in this case light, into sound. As part of the Kepler mission, Jenkins was measuring the light from this star to see whether there were any planets nearby.

Mr. JENKINS: When I started looking at these light curves, when we plot them up on the computer screen, I thought: Well, gosh. What if we played one of these through a sound card, and it said, hello, Earthlings? Unfortunately, we haven't heard that yet. But we have heard a lot of other very interesting things.

BAUGHMAN: Jon Jenkins says this star and the way it pulsates represents a mystery astronomers have grappled with for more than 100 years.

Mr. JENKINS: They understand the basic magnetism causing the pulsations. What they don't understand is they don't understand why the intensity of the pulsations changes over time.

BAUGHMAN: One possible, remote, explanation for this, alien life forms trying to contact us.

Mr. JENKINS: It would be quite awesome to think of an advanced civilization that is so advanced that it could actually modulate the brightness variations of its star. And it's not such a crazy idea. People have actually suggested, in the literature, that a civilization that's sufficiently advanced could actually tickle...

BAUGHMAN: Tickle?

Mr. JENKINS: Tickle it, tickle the star. So in fact we, have some people on our science team who are actually examining stars to see whether they find evidence of this.

BAUGHMAN: So you're suggesting that mysterious, pulsating star could be like an alien's version of a mirror on a desert island?

Mr. JENKINS: That's right. They could be sending us cosmic smoke signals across the galaxy.

(Soundbite of song, "Would You Like to Swing on a Star"))

Mr. BING CROSBY (Singer): (Singing) Would you like to swing on a star...

BAUGHMAN: How do you tickle a star?

Mr. JENKINS: You know, I don't actually know. I think it would be quite complicated. I'm not sure if I'd want to try that. But, you know, the star might actually like it. I don't know.

(Soundbite of ringing)

BAUGHMAN: Very few people know more about sound in space than Don Gurnett.

Mr. DON GURNETT (Physics Professor, University of Iowa): Yes. Hi, Brent.

BAUGHMAN: He's a physics professor at the University of Iowa, and he's been studying and collecting space sounds for more than 40 years.

Mr. GURNETT: I can remember vividly to this day when we turned the transmitter on in this spacecraft and orbited around the Earth. And we heard all these really strange sounds.

(Soundbite of aurora)

BAUGHMAN: This particular sound, one of Don Gurnett's favorites, is the sound of the aurora, the Northern Lights. He's also collected the sound of lightning in Earth's upper atmosphere.

Mr. GURNETT: So he goes (makes noise) like that.

BAUGHMAN: There's one sound in particular from Saturn's aurora - yup, Saturn has an aurora - that is so strange you can find groups of people online who are convinced it's proof of aliens.

(Soundbite of aurora)

Mr. GURNETT: I know. I've heard that. I don't endorse that point of view. But nonetheless, it's pretty bizarre.

(Soundbite of aurora)

SETI director Jill Tarter says aliens would probably not sound like this. Saturn's signal is what's called an astrophysical signal, meaning it occurs naturally in space. SETI looks for a signal that doesn't.

Ms. JILL TARTER (Director, Search for Extra-Terrestrial Intelligence): A signal that shows up at only one channel on the radio dial, as opposed to being spread over many channels.

(Soundbite of static)

BAUGHMAN: This is an artificial example of what the SETI Institute is looking for. That high-pitched whistle you hear is a signal that occurs on just one frequency. Nature can't produce such a sound.

Ms. TARTER: Nature tends to be broadband. Technology can be broadband, but we can also produce these very narrow-band artifacts that are a dead giveaway that that's some engineering there.

BAUGHMAN: And engineering could mean extraterrestrial life.

NASA's sharing of the Kepler discovery with SETI represented a change in the way the two agencies have worked in the past. And Jill Tarter says it could mean SETI will work more closely with NASA in the future to determine where habitable planets might be and where to turn their telescopes.

Ms. TARTER: As Carl Sagan said, we are all made out of stardust. You are actually made out of the remnants of that star that blew up billions of years ago. And the connectedness of life to the cosmos and the idea of thinking about maybe life somewhere else I think has the opportunity to trivialize the differences among humans on this planet that we find so troublesome.

WERTHEIMER: Jill Tarter spoke to our producer, Brent Baughman. You can hear more space sounds on our website, npr.org.

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