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[Music]

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nasa's test mission has found its first

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earth-sized world in its star's

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habitable zone

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this means the planet called toi 700d

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has the potential for liquid water on

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its surface

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test stares at patches of sky for long

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stretches recording light from thousands

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of stars

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some of these stars have planets that

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cross or transit in front of them

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tess sees these events as tiny regular

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dimmings of the host's stars

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one star where tess saw transits is toi

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700 it's a red dwarf about 40 percent

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the mass and size of our sun and roughly

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half its temperature

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one set of transits announced the

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presence of a planet close to the star

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called toi 700b

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another set revealed a second planet

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named toi 700c a little farther out

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the deeper shorter transit means the

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planet is larger than the first and the

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plane of its orbit is slightly tipped

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a final set of transits showed toi 700d

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orbiting even farther out

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tess observed the system for nearly 11

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months and saw each planet transit

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multiple times

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scientists determine that the inner and

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outer planets are almost earth size and

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may be rocky

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the middle world is more than twice as

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large and most likely made of gas

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all three may be tidally locked rotating

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just once each orbit so the same side

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always faces the star

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but most importantly toi 700d is within

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the star's habitable zone

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scientists wanted independent

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confirmation of toi 700d so they

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monitored its star with nasa's spitzer

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space telescope

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spitzer saw a clear transit from the

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outer planet affirming its existence and

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improving scientist certainty of the

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planet's size

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toi 700d is one of only a few

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earth-sized planets found in potential

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habitable zones

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others include discoveries by kepler and

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several planets in the trappist-1 system

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because toi 700 is bright and nearby the

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planets are good candidates for precise

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mass measurements by ground-based

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telescopes

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future missions may also tell us if the

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worlds have atmospheres but scientists

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need to know what kinds of signals to

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look for

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researchers at nasa's goddard space

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flight center created models of the

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planet to explore its potential

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conditions

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one version is a water covered world

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with an atmosphere similar to early mars

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but denser another looks like a

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completely dry version of today's earth

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both models have vastly different

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surface temperatures

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light passing through their atmospheres

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creates distinct signals because

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different molecules are present

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by simulating these data now scientists

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can make predictions for real future

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observations and narrow the range of toi

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700d's possible conditions

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we still have much to learn about the

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toi 700 system but thanks to tess

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spitzer and the work of many scientists