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Listen to part of a lecture in an astronomy class.

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(male professor) We\'ve been discussing the search for exoplanets——planets located outside our solar system.

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Studying exoplanets really helps us put our solar system into context.

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For example, the features of the planets in our solar system relatively common or uncommon compared to planets and other solar systems.

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Now, most of the exoplanets found so far are large gas giants, planets that resemble Jupiter, because of their size, they\'re relatively easy to detect from earth.

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But we also want to learn about smaller rocky exoplanets that resemble earth, especially because we\'re interested in exoplanets that could theoretically support life.

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One rocky exoplanet we actually have a lot of information about is 55 Cancri e.

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55 Cancri e is about twice the size of earth and 8 times the mass.

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This exoplanet is located very close to the sun-like star at orbits.

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That is to say, its star is about the same size and temperature as the sun. And being that close has some interesting effects.

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First of all, 1 year on 55 Cancri e is very short, just 18 hours long. From a research’s perspective, that\'s pretty convenient.

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You see, one way astronomers gather information about exoplanets is by observing distant stars using telescopes in orbit around earth.

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These telescopes gather light emitted by stars, including any changes in the intensity of that light.

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So, when an exoplanet passes between its star and the earth, the stars light dims temporarily. And our telescopes can detect this slight change in intensity.

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Now, this happens once in each exoplanet yearly orbit around its star.

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As a researcher, you\'d rather that happen once every 18 hours than once every 500 days, right?

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Now, a recent study provided enough information about 55 Cancri e to create a detailed temperature map of the planet.

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One interesting feature of this planet is that the same half of 55 Cancri e always faces the star, and the other half faces away from the star.

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Now, researchers believe the entire planet is almost completely covered with lava.

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If true, this could help explain the surprising temperature conditions on the planet.

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You see, we\'d expect the sunny side of the planet to be hotter than the other side, because it\'s directly exposed to the radiation of the star.

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But a lot of that heat should circulate around to the cooler side of the planet through the lava.

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However, on 55 Cancri e the sunny side is much hotter by about 1,000 degrees Celsius.

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We think this extreme temperature differential is due in part to the planet\'s thin atmosphere.

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The heat doesn\'t circulate around the planet through the atmosphere, nor does it circulate through the lava.

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Much of the lava on the cooler side has solidified or is very thick or viscous.

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But the lack of a heavy atmosphere doesn\'t entirely explain the temperatures found on 55 Cancri e.

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The planet is still hotter than we\'d expect it to be, based on the amount of radiation it receives from its star. So, there must be an alternative source of heat.

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Another possibility is a process known as tidal dissipation.

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Tidal refers to the gravitational force, one planetary body has on another. Dissipation refers to the spreading out of this force.

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In this case, tidal dissipation is the effect the gravity of its star has on the distribution of heat on 55 Cancri e.

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Since 55 Cancri e is so close to its star, the star’s gravitational pull is very strong.

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This gravitational pull could put enough pressure, create enough friction within the planet to generate a significant amount of additional heat.

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Basically, the planet might be boiling from the inside out, but this still can\'t completely account for the temperature.

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There is something going on inside the planet, something that is producing the heat that we still don\'t understand.

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Now, when you think about it, it\'s pretty amazing how different this planet is from earth.

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It\'s a good reminder that just because an exoplanet is relatively similar in size to earth, that doesn\'t mean it will be like earth.

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Learning about the extreme conditions on a place like 55 Cancri e really makes you think.

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After all these years of studying exoplanets, I\'m always amazed by the rarity of the life supporting conditions on earth.

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Of course, that doesn\'t mean we shouldn\'t keep looking for rocky exoplanets that might be more habitable than 55 Cancri e.

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We\'ve seen what large hot stars can do to an exoplanet’s temperature, but if a star is small and cool, planets could have a close orbit without being subject to tidal dissipation.

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