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I am holding something remarkably old.

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It is older than any human artifact,

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older than life on earth,

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older than the continents [br]and the oceans between them.

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This was formed over 4 billion years ago[br]in the earliest days of the solar system

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while the planets were still forming.

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This rusty lump of nickel and iron[br]may not appear special.

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But when it is cut open,

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you can see that is differently[br]from earth lymetals.

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This pattern reveals metallic crystals[br]that can only form out in space

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where molten metal can cool[br]extremely slowly,

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a few degrees every million years.

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This was once part of a [br]much larger object,

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one of millions left over[br]after the planets formed.

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We call these objects asteroids.

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Asteroids are our oldest[br]and most numerous cosmic neighbors.

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This graphic shows near-earth asteroids[br]orbiting around the sun,

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shown in yellow,

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and swinging close to the earth's orbit,[br]shown in blue.

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The sizes of the earth, sun and asteroids[br]have been greatly exagerrate

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so you can see them clearly.

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Teams of scientists across the globe[br]are searching for these objects,

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discovering new ones everyday,

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steadily mapping near-earth space.

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Much of this work is funded by NASA.

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I think of the search for these asteroids[br]as a giant public works project.

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But instead of building a highway,[br]we're charting outer space,

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building an archive that will last[br]for generations.

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These are the 1,556 near-earth asteroids[br]discovered just last year.

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And these are all of the known[br]near-earth asteroids,

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which at last count was 13,733.

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Each one has been imaged, catalogued,[br]

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and had its path around [br]the sun determined.

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Although it varies from asteroid[br]to asteroid,

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the paths of most asteroids[br]can be predicted

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for dozens of years.

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And the paths of some asteroids[br]can be predicted with incredible precision.

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For example, scientists at the [br]jet Propulsion Laboratory[br]

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predicted where the asteroid Toutatis[br]was going to be

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four years in advance within[br]30 kilometers.

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In those four years, Toutatis[br]travelled 8.5 billion kilomters.

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That's a fractional precision [br]of 0.000000004.[br]

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(Laughter)

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Now the reason I have this [br]beautiful asteroid fragment

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is because, like all neighbors,[br]asteroids sometimes

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drop by unexpectedly.

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Three years ago today,

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a small asteroid exploded[br]over the city of Chelyabinsk, Russia.

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That object was about 19 meters across,

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or about as big as a convenient store.

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Objects of this size hit the earth[br]every 50 years or so.

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66 million years ago,

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a much larger object hit the earth,[br]causing a massive extinction.

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75 percent of plant and animal species[br]were lost,

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including, sadly, the dinosaurs.

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That object was about [br]10 kilometers across,

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and 10 kilometers is roughly[br]the cruising altitude

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of a 747 jet.

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So the next time you're in an[br]airplane,

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snag a window seat, look out

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and imagine a rock so enormous that[br]resting on the ground,

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it just grazes your wingtip.

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It's so wide, that it takes your[br]plane 6 full minutes

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to fly past it.

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That's the size of the asteroid[br]that hit the earth.

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It has only been within my lifetime[br]

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that asteroids have been considered[br]a credible threat to the planet.

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And since then, there's been [br]a focused effort underway

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to discover and catalogue [br]these objects.

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I am lucky enough to be part[br]of this effort.

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I'm part of a team of scientists[br]that use NASA's