n July 16, 1994, scientists there anything we could do to stop BY NANCY HONOVICH around the world turned the impact before it happens? Shara their telescopes toward discusses the possibilities. Jupiter to watch an amaz- ing event. A number of icy Why do space objects collide Oobjects known as the Shoemaker-Levy 9 in the first place? comet hurtled toward the giant planet All objects in the universe—such as at a speed of 60 kilometers (37 miles) asteroids, comets, planets, and stars— per second. As the comet hit the planet, experience gravity. This pulling force ou s e? it caused huge shock waves, which causes the objects to tug on each other r ? lifted large clouds of gas into the upper and to change each other’s path. Some- sh C part of the atmosphere. times, two objects move toward the a When the blasts were over, Jupiter same place at the same time. Because Cr was left with a few scars: Gray areas of these objects don’t have eyes, they gas and dust had formed in the planet’s don’tdon’t knowknow toto getget outout ofof thethe way.way. atmosphere and remained there for Sometimes,Sometimes, theythey collide.collide. Scientists wonder if a space several months. But for scientists—and anyone else who observed the AreAre anyany ofof thesethese When the Shoemaker-Levy 9 event—the effects were more objectsobjects headedheaded comet struck Jupiter, rock could destroy life on Earth. lasting. People everywhere were our way? it caused dark left wondering: Could this hap- Yes,Yes, many.many. ButBut spots to form on pen to Earth? they won’twon’t strikestrike the planet. After seeing Shoemaker- Earth any- Many scientists Levy 9 crash into Jupiter, people time soon. An predict that if began to pay closer attention asteroid called an asteroid were to objects that could strike MN4 will come to crash into Earth. These objects include within 35,400 Earth, the impact comets much like Shoemaker- km (21,997 mi) of would look like a Levy 9 and, more important, EarthEarth on AAprilpril 13, fireball. large asteroids. As many of 2029. That’sThat’s prettypretty these objects move around the close,close, especially when ScientistScientist MikeMike SharaShara atat thethe AmericanAmerican sun, their paths sometimes youyou figurefigure that the moon MuseumMuseum ofof NaturalNatural HistoryHistory take them within 160,934 km is about 385,000 km (240,000 mi) (100,000 mi) of Earth. That may from Earth. And the asteroid is large. It seem far, but for most scientists, it’s a measures about 300 meters (984 feet) little too close for comfort. across—that’s about three times the Mike Shara, an astrophysicist (a- length of a football field. stroh-fih-zih-sist) at the American Museum of Natural History in New During its close flyby, will we be York, studies how objects in the uni- able to see MN4 from Earth? verse collide. He estimates that a space It depends on where you are and how object the size of a cruise ship narrowly clear it is outside. If the night is clear, misses Earth about every 10 years. it’ll appear almost as bright as the stars Could one of these objects actu- in the Big Dipper. The best views will be ally strike our planet? And if so, is from Asia, Europe, and Africa.

DAVID A. HARDY/SPL/PHOTO RESEARCHERS, INC. (ASTEROID); PHOTO BY DENIS FINNIN. © AMERICAN MUSEUM OF NATURAL HISTORY (SCIENTIST); JUPITER (NASA) For more information, go to: www.scholastic.com/spacecrash

12 SUPERSCIENCE JANUARY 2006 13 ROCK AROUND THE SUN As MN4 circles the sun, its path A meteorite will take it very close to Earth. that crashed into MN4 Gravity Game You’ll Need 3 Empty, quart- 3 Pencil Earth caused EARTH Barringer size cardboard 3 Paper clip How does gravity affect different objects? milk carton Crater. 3 Clay 3 Scissors SUN THINK: Suppose you and your teacher were to weigh 3 1 cup of dry 3 Thick rubber Cheerios cereal yourselves on a scale. Who would weigh more? band 3 1 cup of jelly PREDICT: Gravity is a force that pulls all objects toward 3 Piece of twine, beans one another. It is the same force that pulls objects towards 36 cm (14 in.) long 3 1 cup of Earth. The more mass an object has, the greater the pull of uncooked rice 3 Ruler gravity. Suppose you had three equal-sized cartons: one full of cereal, one full of jelly beans, and one full of rice. Which

has the most mass? Which experiences the most gravity? STEP 4 What would happen if an boulders out of the ground. These object has a lot of mass, gravity Procedure: q 6. Place a piece of clay on asteroid like MN4 were to boulders would crash back down would cause it to tug gently on the q 1. Cut the milk carton into the floor against a wall. Stick strike Earth? all over Earth for the next few days. asteroid. Over time, this object’s 2 pieces—the bottom part one end of the ruler into the It would not mean the end of It’s also possible that MN4 would pulling force would move the should measure 7.5 centime- clay. The ruler should be up- right against the wall. Have a life on Earth, but it would still turn into a fireball, which would asteroid out of the way. ters (3 inches) high. Keep the friend grasp the scale by the be terrible. In Arizona, there is set off forest fires for hundreds of bottom part, but throw the rubber band and hold it so a hole in the ground that mea- miles. The fires would then release top part away. What would you say to kids that the top of the carton is sures roughly one mile across. huge amounts of ash into the atmo- who are scared that a large q 2. Choose one side of the even with the top of the ruler. This hole, called Barringer Crater, sphere—and that might block out asteroid will crash into Earth? carton and measure 2.5 cm was formed by a meteorite that light from the sun. If it were to crash Scientists are scanning the sky Pour the cereal into the (1 in.) down from the top. q 7. Thread one end of crashed into Earth about 50,000 into the ocean, it would cause a all the time to make sure that a Using a pencil, poke a hole carton. This is carton 1. twine through each hole. years ago. MN4 is about 10 times giant tsunami, or wave, which large asteroid isn’t headed our through this area. Make sure Watch the carton drop bigger than that meteorite. It has could destroy many coastal cities. way anytime soon. The chance the hole is centered. q 8. STEP a thousand times more mass and that Earth will be struck by a large alongside the ruler. Mea- would release a lot more energy If scientists discovered that asteroid or comet during your q 3. Repeat Step 2 on the sure how many centimeters 8 or inches the carton has as it crashed. So just imagine the a large asteroid was headed lifetime is almost zero. opposite side of the carton. dropped. Be sure to measure size of the crater it would cause! towards Earth, what could we from the top of the carton. do to prevent a collision? q 4. Create a handle for your Words to Know carton: Thread one end of Would you be affected if you There are many possible solu- Comet — a ball of ice, rock, and twine through each hole. q 9. Empty the carton. lived far from the impact site? tions. One idea is to take an object frozen gases that circles a star Tie a knot at each end. Yes. If MN4 were to crash on that has a lot of mass up into space Atmosphere — the layers of gas that q 10. Repeat Steps 7 to 9 land, it would blow billions of and park it within a few hundred surround a planet q 5. Attach a paper clip to the using jelly beans instead of yards of the asteroid. Because that Asteroid — a rock that moves around top of the string handle and a cereal. This is carton 2. the sun and is smaller than a planet rubber band to the other end or a moon q Repeat Steps 7 to 9 check it out of the paper clip. You now 11. In early 2006, the American Museum of Natural History’s Hayden Planetarium Astrophysicist — a scientist who have a spring scale! using rice instead of cereal. studies the universe This is carton 3. Watch the carton of cereal drop in the Rose Center for Earth and Space will open a new Space Show that journeys alongside the ruler. through the night sky to explore collisions of meteorites, stars, and galaxies that Gravity — the pulling force between shape our universe. The Museum has been researching and celebrating the natural objects Conclusions ALL PHOTOS JAMES LEVIN STUDIO world for more than 135 years, and has more than 30 million objects in its entire Meteorite — a space rock that has 1. Which carton was pulled the most by gravity? Which was pulled the least? collection. The Museum’s 200 scientists travel around the world on 100 field expe- hit Earth ditions each year, studying everything from wasps to ocean life to the universe. Mass — the amount of matter in an 2. Based on your findings, which carton had the most mass? To learn more, ask your teacher, or go to www.amnh.org. object 3. Suppose scientists discovered two equal-size objects but didn’t know what they were made of. CHARLES O’REAR/CORBIS (METEORITE) Could the scientists determine which one would be pulled the most by Earth’s gravity?

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