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Humans have observed comets [br]for thousands of years

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as their orbits have brought them within[br]visible distance of Earth.

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Appearing throughout historical records,[br]

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these mysterious lights that [br]came out of nowhere

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and disappeared after a short while

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were thought to be ill omens of[br]war and famine,

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or the wrath of gods.

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But recent research has revealed that[br]comets may be even more deeply connected

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to humanity and our presence on Earth

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than any of these mythical [br]explanations suggested.

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When you think of our Solar System,[br]you probably imagine the nine,

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sorry eight, planets orbiting the Sun.

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But beyond Neptune,[br]far from the heat of the Sun,

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there is a sparse ring found [br]formed by icy chunks

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ranging from the size [br]of marbles to that of small planets.

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And thousands of times farther at the[br]outer reaches of the Solar System

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lies a spherical cloud of small [br]fragments and gases.

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Many of these ancient clumps of stardust[br]are leftovers from the formation

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of the Solar System 4.6 billion years ago,

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while some of the most distant may even[br]come from a neighboring system.

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But sometimes the gravity from [br]passing planets or stars

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pulls them toward our sun,

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beginning a journey that can take up to[br]millions of years.

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As the frozen object travels further[br]into the Solar System,

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the sun grows from a distant spark[br]to an inferno,

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melting the ice for the first time[br]in billions of years.

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Gas and steam eject dust into space,

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forming a bright surrounding cloud,[br]called a coma,

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that can grow even larger than[br]the sun itself.

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Meanwhile, the intense stream of [br]high-energy particles

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constantly emitted by the Sun,[br]known as the solar wind,

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blows particles away from [br]the comet's core,

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forming a trail of debris up to millions[br]of miles long.

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The ice, gas and dust reflect [br]light glowing brightly.

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A comet is born, now orbiting the sun[br]along with the rest of the objects

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in our Solar System.

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But as the comet travels through[br]the Solar System,

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the solar wind tears apart and recombines[br]molecules into various compounds.

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In some of the compounds that[br]scientists found,

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first in the rubble left by a meteorite[br]that disintegrated above northern Canada,

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and then in samples collected by a space[br]craft from a passing comet's tail,

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were nothing less important than[br]amino acids.

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Coming together to form proteins[br]according to the instructs encoded in DNA,

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these are the main active components[br]in all living cells,

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from bacteria to blue whales.

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If comets are where these building blocks[br]of life were first formed,

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then they are the ultimate source of[br]life on Earth,

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and, perhaps, some of the other places[br]they visited as well.

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We know that planets orbit nearly every[br]star in the night sky,

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with one in five having a planet[br]similar to Earth in size and temperature.

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If Earth-like planets and the molecules[br]found in DNA are not anomalies,

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we may be only one [br]example of what's possible

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when a planet under the right conditions[br]is seeded with organic molecules

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by a passing comet.

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So, rather than an omen of death,

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the comet that first brought [br]amino acids to Earth

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could have been a portent of life,

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a prediction of a distant future,[br]where creatures of stardust

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would return to space to find [br]the mysteries of where they came from.