English subtitles for clip: File:Hubblecast 97.webm

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For as long as humans have known that the stars in the sky

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are other suns, they have been asking themselves:

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Are these suns orbited by other planets? Is there life out there?

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Are we alone in the Universe?

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Since the discovery of the first exoplanet only 25 years ago,

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Hubble is among the many instruments

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trying to answer these questions.

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And astronomers are using it to hunt for life on other worlds.

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Hubble, exoplanets and the hunt for life

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25 years have passed since the first exoplanet was discovered

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and eight years since Hubble made its first direct image of an alien world.

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While in the beginning we knew of only a few, very massive exoplanets

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— most often close to their parent star —

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today we know of more than 3000.

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They are of different sizes

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and orbit various types of stars at different distances.

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But one thing hasn’t been found so far: proof of life.

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Despite all the progress made in recent decades,

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the hunt for exoplanets is still a challenging one.

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They hide in the shadows, giving off no light of their own.

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Any starlight they reflect is swamped

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by the overwhelming brilliance of their parent star.

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This makes it especially difficult to find Earth-sized planets

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in the so-called habitable zone — the region around the star

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where liquid water can exist on the surface of a planet.

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And water is essential to all life as we know it.

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Water only remains liquid within a narrow range of temperatures.

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If a planet orbits too close to a star, the water evaporates.

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Too far away and it will freeze.

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The thin band between these extremes, the habitable zone,

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represents the most probable abode of alien life.

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So if we know where to look,

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how will we know if alien life exists on a faraway planet?

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No currently available or planned telescope

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is able to resolve the surface of a planet.

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But radio telescopes keep listening for messages

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from other civilisations, in the hope that they are as curious as we are.

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We could also be lucky and find signs of advanced civilisations.

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Something like a ringworld, a giant artificial structure built around a star.

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But the chances of such a discovery are rather low.

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In their search for life, optical and infrared telescopes

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focus on the analysis of exoplanet atmospheres.

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Life is capable of changing

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the composition of a planet’s atmosphere on a grand scale.

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The oxygen in the Earth’s atmosphere was released

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billions of years ago by microscopic organisms.

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If a similar process has occurred on other worlds,

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we may be able to detect it in the spectrum of the planet.

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From late 2016,

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European astronomers will use almost five hundred orbits of Hubble

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— corresponding to just over a month of observing time —

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to make a detailed study of the atmosphere of hundreds

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of already known exoplanets.

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Hubble has studied alien atmospheres before,

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but this programme offers an unrivalled chance

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to learn more about them than ever before.

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The data we gather in the next months from Hubble

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will be a fundamental database for further studies.

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And with the power of the upcoming

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next generation of telescopes in space and on the ground,

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astronomers may be closer than ever before

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to discovering life elsewhere in the Universe.

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Transcripted by ESA/Hubble. Translated by --