Dune. Star Wars. Alien. Science fiction movies love alien worlds, and so do we. But how do scientists find planets outside our solar system in real life? One way is by looking for the stars that wiggle. Historically, astronomers have measured those wiggles via the Doppler method, carefully analyzing how the star's light shifts. Thanks to new data from the GAIA telescope, scientists have a much better picture of distant stars' wiggles — and the exoplanets that cause them.Want to hear more about exoplanet discoveries? Send us an email at [email protected]. Listen to every episode of Short Wave sponsor-free and support our work at NPR by signing up for Short Wave+ at plus.npr.org/shortwave.Learn more about sponsor message choices: podcastchoices.com/adchoicesNPR Privacy Policy
Chapter 1: What are exoplanets and how were they discovered?
Growing up, you might have learned the names of the planets. Mercury, Venus, Mars, Jupiter. But what about Beta Pictoris C? You probably didn't learn that one. I didn't either. That's because we only found out about it in 2019. And because it's an extrasolar planet, or an exoplanet.
Well, an exoplanet is a planet, but it doesn't orbit the sun. It orbits some other star in the galaxy.
That's Josh Wynn. He's an astronomer at Princeton University and an exoplanet hunter.
And the study of exoplanets is one of the newest and most exciting areas of astronomy. It really only got going in the mid-1990s.
Scientists have found thousands of exoplanets since then by relying on a little trick of gravity.
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Chapter 2: How do planets cause their stars to wiggle?
When a planet is orbiting a star, it's because the star's gravity is pulling on the planet. But forces come in pairs. If the star is pulling on the planet, the planet has to be pulling on the star with the same force.
Compared to the planet, the star is massive, so the pull of gravity from the planet doesn't make it move much.
But nevertheless, it does cause it to move.
Basically, planets make their stars wiggle. But we haven't always been able to directly observe this wiggle. Our telescopes just haven't been sensitive enough to detect it. So in the past, we've mainly used other methods instead. And these methods...
They're very good at finding planets that have small orbits that are located close to the star, kind of like Mercury and Venus and the Earth.
But those planets are only part of the story. Without a way to find planets far from their stars, scientists haven't been able to paint a full picture of these solar systems until now.
This new method, which is called the astrometric method, is actually best at finding distant planets. Planets like Jupiter, Saturn, Uranus, and Neptune around other stars.
This new method lets us fill in the gaps of the picture, finding planets that astronomers couldn't detect before.
This is the beginning of the next big phase of exoplanet discovery. A few years from now, we're going to be in a position to use this technique to find potentially thousands of new exoplanets, and they're going to be different from the ones that we already know about.
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Chapter 3: What are the main methods used to find exoplanets?
Sure. We have two main methods that have led to most of the discoveries. As of today, there are about 5,800 known exoplanets.
Right.
And about 4,000 of them come from a very clever trick, which is based on eclipses. If a planet's orbit happens to carry it directly in front of the star that it orbits, then it will block a little bit of that star's light. And we can tell because the star appears to get slightly fainter for a few hours. That's called the transit method. We say the planet is transiting across the star.
Chapter 4: How does the transit method detect exoplanets?
Mm-hmm.
But the transit method, while it's a wonderful technique, it has the serious problem, which is that it requires a very special coincidence for the orbit to be oriented just right so that from our vantage point, we see these eclipses.
Yeah.
And so it misses most of the planets that are out there.
Chapter 5: What are the limitations of the transit method?
It makes me think of like a lighthouse, right? Like if you're not at the right angle, if you were a helicopter above the lighthouse, you would not see like the beam of light hitting you. You could miss it.
That's right. So if there are aliens viewing our solar system from every possible direction, only one out of 200 of them would ever see the Earth go directly in front of the sun.
Mm-hmm.
Now, the second best method, and really the first one that worked in the mid-1990s, is based on sensing the motion of the star. And we can detect the motion of the star using a trick called the Doppler effect.
Chapter 6: How does the Doppler effect help find exoplanets?
Chapter 7: What is the astrometric method and how will it improve exoplanet discovery?
But those planets are only part of the story. Without a way to find planets far from their stars, scientists haven't been able to paint a full picture of these solar systems until now.
This new method, which is called the astrometric method, is actually best at finding distant planets. Planets like Jupiter, Saturn, Uranus, and Neptune around other stars.
This new method lets us fill in the gaps of the picture, finding planets that astronomers couldn't detect before.
This is the beginning of the next big phase of exoplanet discovery. A few years from now, we're going to be in a position to use this technique to find potentially thousands of new exoplanets, and they're going to be different from the ones that we already know about.
So today on the show, the next phase of exoplanet discovery, how scientists are filling in missing pieces of a solar system puzzle, and how this search has just begun. I'm Regina Barber, and you're listening to Shortwave, the science podcast from NPR.
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It's called in game theory a trigger strategy, or sometimes called grim trigger, which sort of has a cowboy-esque ring to it. To what exactly a sovereign wealth fund is.
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