Josh Wynn
Appearances
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How Do Astronomers Find Exoplanets? Wiggles!
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.
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How Do Astronomers Find Exoplanets? Wiggles!
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.
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How Do Astronomers Find Exoplanets? Wiggles!
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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How Do Astronomers Find Exoplanets? Wiggles!
Sure. We have two main methods that have led to most of the discoveries. As of today, there are about 5,800 known exoplanets.
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How Do Astronomers Find Exoplanets? Wiggles!
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.
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How Do Astronomers Find Exoplanets? Wiggles!
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.
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How Do Astronomers Find Exoplanets? Wiggles!
And so it misses most of the planets that are out there.
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How Do Astronomers Find Exoplanets? Wiggles!
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.
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How Do Astronomers Find Exoplanets? Wiggles!
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.
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How Do Astronomers Find Exoplanets? Wiggles!
Now, the term Doppler probably rings a bell because of a Doppler radar that's used to measure the speed of a car or the speed of raindrops falling from the sky. It's the effect that you get whenever you have a source of waves that's moving relative to the observer, and light is a wave.
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How Do Astronomers Find Exoplanets? Wiggles!
So if a star is moving towards us, then the light rays that it emits by the time they reach the Earth appear to be shifted in their wavelength.
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How Do Astronomers Find Exoplanets? Wiggles!
Exactly. Yeah. We can actually hear those changes. Like you said, if a car goes by, we hear it go...
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How Do Astronomers Find Exoplanets? Wiggles!
Now, the speed of light is huge compared to the speed of sound.
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How Do Astronomers Find Exoplanets? Wiggles!
Yeah. So when we divide by the speed of light, we get this tiny undetectable effect to our eyes.
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How Do Astronomers Find Exoplanets? Wiggles!
But as astronomers, our whole job is to figure out how to analyze starlight very, very precisely. So we have specialized equipment that can detect these tiny shifts in wavelength.
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How Do Astronomers Find Exoplanets? Wiggles!
Astrometry is actually one of the oldest techniques in astronomy. It means measuring the position of the star in the sky. So if you can measure exactly where it is on the sky, you are doing astrometry.
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How Do Astronomers Find Exoplanets? Wiggles!
That's right. Measuring the coordinates of the star in the sky.
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How Do Astronomers Find Exoplanets? Wiggles!
Right. The astrometric method is conceptually simpler. We're just seeing the star move in the sky, wiggling back and forth. Now, we can't literally see it with our eyes. These motions are way too small.
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How Do Astronomers Find Exoplanets? Wiggles!
The big difference is that the astrometric method, where you're seeing the star wiggle on the sky, is better at finding distant planets, planets with very wide orbits.
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How Do Astronomers Find Exoplanets? Wiggles!
Well, an exoplanet is a planet, but it doesn't orbit the sun. It orbits some other star in the galaxy.
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How Do Astronomers Find Exoplanets? Wiggles!
It's because the further away the planet is from the star, the larger its orbit, and that also makes the star's orbit wider, too.
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How Do Astronomers Find Exoplanets? Wiggles!
And since if we're trying to see the star wiggle, we want the star to be moving as far as possible. Right. So the wider the orbits, the better.
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How Do Astronomers Find Exoplanets? Wiggles!
Yeah, the big game changer was a European space mission called Gaia. They launched a telescope in 2013. It's actually two telescopes, and they're pointing in different directions. And the telescope is spinning around.
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How Do Astronomers Find Exoplanets? Wiggles!
In space. So it's a spinning platform with two telescopes. And what the telescope is doing is it's measuring the exact time at which a star crosses through the field of view of each telescope. So every time it rotates and sees a certain star, it clocks that moment.
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How Do Astronomers Find Exoplanets? Wiggles!
And if you have billions of such measurements, then you can calculate the exact positions of all of those stars with the utmost precision.
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How Do Astronomers Find Exoplanets? Wiggles!
So the team that operates the Gaia telescope prepared a list of about 75 stars that appeared to be wiggling back and forth. And so our idea was, okay, these appear to be new planets from the astrometric method. Let's use the Doppler method to see if we can confirm them.
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How Do Astronomers Find Exoplanets? Wiggles!
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.
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How Do Astronomers Find Exoplanets? Wiggles!
And as it turns out... Most of those 75 objects are not exoplanets. They are something else. Yeah. So the one that we found came from a long kind of sifting through of these candidates, ruling out most of them and arriving at so far just one that we're pretty sure is an exoplanet.
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How Do Astronomers Find Exoplanets? Wiggles!
Sure. It is an unusually massive planet. It's almost 12 times the mass of Jupiter. Oh, wow. Wow. You might call it a super Jupiter.
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How Do Astronomers Find Exoplanets? Wiggles!
It's orbiting around its star every 571 days. What? It's lower in mass and redder and less luminous than the sun.
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How Do Astronomers Find Exoplanets? Wiggles!
And it is located about 240 light years away.
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How Do Astronomers Find Exoplanets? Wiggles!
Yeah, it ran for more than 10 years, diligently collecting data and measuring the locations of all these billion or so stars. But eventually, you know, all good things must come to an end. It ran out of fuel and it won't be conducting any more observations.
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How Do Astronomers Find Exoplanets? Wiggles!
Exactly, yeah. So about a year and a half, maybe two years from now, we're going to have a much larger set of data that they're busy processing right now. And that should lead to the detection of at least hundreds and probably thousands of new exoplanets.
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How Do Astronomers Find Exoplanets? Wiggles!
Well, imagine what it would be like if we didn't know about Jupiter or Saturn or Uranus or Neptune in our own solar system. We would have a really incomplete picture of what's going on around the sun. And We want to have the same kind of complete knowledge of exoplanetary systems.
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How Do Astronomers Find Exoplanets? Wiggles!
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.
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How Do Astronomers Find Exoplanets? Wiggles!
We want to know about the little planets, the big planets, the nearby planets to the star, and the more distant planets, so that we can see what are the relationships between them, what are the patterns that hold in those systems, and how do they compare to what we observe in our system. It's hard to draw any conclusions when you're basing all your conclusions on one example, the solar system.
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How Do Astronomers Find Exoplanets? Wiggles!
You really want thousands of data points. And you want complete knowledge of those systems before you can be confident about any patterns that might exist.