How do we find new planets?

JACKIE FAHERTY (senior scientist, Division of Earth and Physical Sciences, American Museum of Natural History): How do we find new planets?

[FAHERTY on screen speaking to camera. Text appears: “How do we find new planets?”]

[MUSIC] [BOOM]

[The American Museum of Natural History logo appears. Below it, text appears: “Space Vs Dinos.” It is superimposed over illustrations of an asteroid and a dinosaur skull. FAHERTY reappears on screen. Text reads “Jackie Faherty, astrophysicist”]

FAHERTY: So we've known about planets like Mercury, Venus, Mars, Jupiter, and Saturn

[To the left of FAHERTY, spheres in roughly successive sizes appear, labeled as Mercury, Venus, Mars, Jupiter, and Saturn. 

FAHERTY: as long as we've been looking up as they were obvious objects in the nighttime sky - bright objects that move different than the stars do.

[The planets scale down and join a starry sky. Text in the bottom right reads Day 1, Day 2… increasing. As it increases, we can see that the planets, which are slightly larger and brighter than the stars, are also moving in different directions than the stars, which are mostly moving up and to the right. Text reads “*ok we exaggerated a little but you get the point.” FAHERTY reappears on screen.]

FAHERTY: And the way that I can say that we detected them would be with your eye

[To the left of FAHERTY, a big circle blinks to reveal an eye. It blinks again to reveal the text: “Direct Imaging”]

FAHERTY: or with direct imaging. So you directly detected those planets.

[A globe of Earth drops down and an illustration of an astronomical observatory drops on top of it.]

[RADAR SOUNDS]

FAHERTY: In today's world, we're searching for planets around other stars,

[Dashed lines coming from the observatory reveal a star, which has a small planet orbiting around it.]

FAHERTY: objects that we call exoplanets.

[Text appears, coming from the observatory: “I spy with my huge eye… an EXOPLANET!”]

FAHERTY: And this direct imaging method is actually something that we try as well,

[A photo from a telescope of exoplanets HR 8799B, C, D, E  around star HR8799.]

FAHERTY: just with far more complicated instrumentation,

[A photo from a telescope of exoplanet 2M1207b around star 2MS1207.]

FAHERTY: so we haven't found that many planets that way.

[Text appears: “>20 planets found using direct imaging as of 2018.” Faherty reappears on screen.]

FAHERTY: But there are other methods that astronomers use as well. One of the most popular and productive is called the transiting method.

[Text appears: “Transiting method.” An illustration of a bright star fills the screen.]

FAHERTY: You can see the light of a star dip ever so slightly

[The light from the star seems to grow dimmer suddenly every so often. A “Bright-o-meter” appears to the left of the star. When the star dips in brightness, the Bright-o-meter also dips in the meter.] 

FAHERTY: in a cyclic pattern due to a planet moving in front of it from Earth’s perspective.

[A planet and its orbit around the star, which appears as a dashed circle around the star, fade into the image. We can see that when the planet moves around the front of the star, the light of the star decreases.] 

FAHERTY: So we watch thousands upon thousands of other stars

[The camera slowly pulls back to reveal several of these stars with “Bright-o-meters”, some decreasing in brightness and some not.] 

FAHERTY: and we look for tiny dips in the light. Thousands of planets have been found that way.

[FAHERTY appears in a pop up bubble next to the text: “>3,000 planets found using transiting as of 2018.” FAHERTY reappears on the screen.]

FAHERTY: Other methods take advantage of something called the wobble.

[Text appears: “THE WOBBLE.”]

[THUMPING BEAT]

[The text “THE WOBBLE” bounces up and down, on a background of bouncing planets. Text appears: “The dance craze sweeping the galaxy”]

[RECORD SCRATCH]

[The planets and the text wipe away to offscreen.]

FAHERTY: If you have a big planet

[A brown planet pops onto screen.]

FAHERTY: around a decent-sized star 

[A star appears on screen and the planet begins to orbit it.]

FAHERTY: the planet will tug on the star, causing it to wobble a little bit.

[The star moves slightly in the center of the planet’s orbit. The word “wobble” appears on many sides of the star.]

FAHERTY: So one way that you can see that wobble is through what we call the radial velocity method. 

[FAHERTY reappears on screen. Text appears: “Radial Velocity Method.”]

FAHERTY: And this is where you take the light of a star,

[In front of FAHERTY, a white orb of light appears.]

FAHERTY: and you break it up into its fingerprint.

[The white orb separates into 5 orbs of purple, blue, green, yellow, and red light respectively. They condense into a rainbow gradient rectangle with some black bars in it.]

FAHERTY: And you could see that light fingerprint move towards you or away from you,

[The rectangle with the rainbow gradient moves below an illustrated star with a planet orbiting around it. Lines point to the black lines in the rainbow gradient and text reads: “Unique gaps in light.” The lines start to move from side to side from their original position.”] 

FAHERTY: depending on if the planet is tugging the star towards you or away from you,

[Arrows indicate that the black lines moving closer to the purple end of the rainbow indicates that the star is moving towards Earth, and if the black lines are moving towards the red end of the spectrum it indicates that the star is moving away from Earth.]

FAHERTY: similar to the Doppler effect,

[Text zooms in: “Doppler Effect.] 

FAHERTY: where when a car is coming towards you the sound is higher,

[Two human figures are dropped into the center of the screen. They walk and chat away from the camera.]

[HORN SOUND]

[A line is drawn in from the lefthand side with soundwaves leading it. The text “Higher” appears below it. The two humans jump back slightly.]

FAHERTY: and when the car is pulling away from you it's lower.

[The line dips down lower on the screen as an illustration of a car zooms past the two human figures. The text “Lower” appears below the line. The two humans shake their hands and yell “!!!!” at the car as it speeds away. Text fills the screen: “>700 planets found using radial velocity as of 2018.]

FAHERTY: And the other way

[FAHERTY appears on screen again.]

FAHERTY: you could take advantage of that wobble is something called the astrometric method.

[Text zooms in: “Astrometric method.”]

FAHERTY: And that's where you would very very carefully watch the position of a star

[A star appears in the middle of the screen, wobbling. Three lines draw out from it and three stars appear at the end of these lines. A dashed line indicates the lines connecting these stars with the middle star are “precise distance from reference stars.” As the star in the middle wobbles, we see the lines connecting the reference stars to it change slightly.]

FAHERTY: and you could actually see it jump back and forth due to a planet pulling it towards you or away from you.

[Text appears: “0 planets found using the astrometry as of 2018.”] 

FAHERTY: And while we have yet to discover a planet using this method, there are new catalogs and surveys that will allow us to detect planets this way.

[A starfield photo appears, with a spacecraft hovering in the center. Text appears below the spacecraft: Gaia Space Observatory. The starfield image minimizes to a circle next to Faherty.]

FAHERTY: We now know of thousands of exoplanets orbiting other stars

[On top of the starfield image, text reads “3,800 planets confirmed.]

FAHERTY: and the next generation of telescopes is only going to give us more information and more planets.

[On top of the starfield image, text reads “2,800 planets confirmed.]

And we will soon be able to tell far more stories about the diversity of exoplanets in the galaxy.

[Scientific ideas about what certain exoplanets will look like swing in on picture frames. Text in the center reads, “Exoplanets of the Milky Way.”]

[Credits roll. Faherty appears in the bottom right corner of the screen.]

FAHERTY: There actually may be another planet in our own solar system. We're calling this one Planet Nine. In order to find it you've got to scan the entire sky looking for something that moves. And you can log onto BackyardWorlds.Org – it’s a citizen science project that I help run and you can participate in the search.