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COMETS '

These oosmlc snowbolis are roughty the sizeof a smali town.Whentheir orbit ' bringsthemclosetothesun.theyheatup ' rnMCT MIIPI Cl andspewdustandgasesintoagiant ' Ł»UIYI11 NUULtl glowing head larger than most planets. The \ E^ch comet has a tiny frozen part, calted a dust and gases form a taił that stretches away \ nucleus. otten no blgger than a tew k.lometers from the sun tor milbons of kilometers. \ acf<»S- The nucleus contains icy chunks and (Pictured: Anaglyph ot comet Wild 2 as \ Irozen gases wrth bits ot embedded rock and photographed by NASAs SUrdust mission) \ dust. The nucleus may have a smali rocfcy

^ core.

WHAT’S THAT SPACE ROCK?

A CLASSIFICATION OF SMALL BODIES AND STELLAR OBJECJS

DWARF PLANETS

l&e planets. these bodies. wtiich mostty hail trom the Kulper Belt beyond Neptun*. are massive enough to be shaped by gravitation but don't have enough ot their own gravitatk>nal muscle to influence objects around them. II you're still wondering where Pluto went on the list of planets in our sołar system, look no turther than this category. (Pictured: Aitist's illustration ot Ceres)

ASTEROIDS

These rocky. airtess woritfe lett over from the tormation ot our sołar system orbit our sun. but are too smali to be caiłed planets. They rangę in size from about 900 kilometers (560 miles) in dtameler to less than 1 kiometer (0.6 nule) across. (Pictured: Anaglyph of asteroid Vesta as photographed by NASA s Oawn mission)

\ THE ASTEROID BELT

This vast. doughnut-shaped ring between theorbitsof Mars and Jupiter isknown to contain tens of thousands ot asteroids --' sometimes called "minor planets" •• but it ' may even contain milbons! Most of the \ asteroids in our solar system originated \ in this rock-filled region.

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METEOR SHOWERS

These beautiful stellar fireworks occur when the particles. or meteofoids. trailing a comet rain down and then bum up in Earth's atmosphere. causing hundreds or even thousands ot

NEAR-EARTH OBJECTS

Any space object that passes within 1.3 AU (about 193 million kilometers or 120 million miles) of Earth i$ called a near-Earlh object. ot NEO. NASA Im an otfice whose job is to monitor these objects m case they present any danger to Earth,    •