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[Music]

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Narrator: When it comes to finding planets outside our

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solar system, no space mission to date can beat NASA's Kepler

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in 5 years it has found more than a thousand confirmed exoplanets,

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with thousands more awaiting confirmation. Kepler finds

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exoplanets by carefully watching starlight, looking for slight dips in

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brightness as a planet passes in front of, or transits, its star. This

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technique, called time-series transit photometry, is most effective

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for large planets in close orbits. This both maximizes the light

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loss during a given transit and the number of transits we observe.

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But how far can astronomers go with this technique? Can we

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find a twin of Earth? Or even identify whether a planet has moons?

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With two transit photometry missions on the horizon--NASA's

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TESS and ESA's PLATO--some astronomers have examined the limits

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of this technique, with surprising results. Daniel Angerhausen: For our study,

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Michael Hippke and I combined the knowledge of the

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lessons learned from Kepler with what we know about the future missions like

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TESS and PLATO, and we asked ourself the question 'what would we be able

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to see if we put these  observatories outside our solar system and observed

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our solar system.' And the results are that we

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probably won't be able to see Mars, or Mercury, but

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everything else in our solar system we definitely get a solid detection of

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Earth, a solid detection of Venus. Also of the outer planets.

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We might even be able to see ring structures like the one around

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Saturn, and maybe even moons, Jupiter's moons.

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Narrator: In another study, they pushed Kepler to the limit by cleverly

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combining almost all extrasolar planet data collected by the telescope

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using an understanding of orbital mechanics. Daniel: For example, Jupiter

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has so-called trojan asteroids that collect in two

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specific areas on its orbit, pretty symmetrically to its orbit.

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And in the study that we did on the Kepler data, where we added up

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all the phase curves of all 4,000 planets in the Kepler data set, we were even

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able to see signatures of asteroids in extrasolar

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systems. And with the future missions we might even be able to find that

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in individual systems and not just by putting all the data together.

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We wanted to figure out what the ultimate limit

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is that we can do photometry with, and it turns out

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with the next generation of instruments we're already hitting the technical limit and are

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mostly limited by the variation of the host stars themselves,

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by the huge noise that's coming from the host stars. Narrator: The way to push down

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this noise is by observing stars for longer periods to improve

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models of the star's behavior, allowing astronomers to tease out the smallest transits.

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The work of Hippke and Angerhausen shows

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that future missions will be able to detect Earth-size planets orbiting

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sun-like stars at distances that would allow liquid water.

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These systems will become prime targets for more detailed study, using other

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missions, such as NASA's James Webb Space Telescope.  Will we

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find a copy of our solar system? How common are habitable

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worlds, and particularly twins of Earth? The thousands of exoplanets

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to be discovered by TESS and PLATO will go a long way to providing answers.

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