Science Scoops: Rocking the Earth

The idea of a large rock from space walloping Earth and wreaking havoc among its citizens is not solely the stuff of Hollywood movies such as Armageddon.

Ask any planetary astronomer, and he or she will tell you that our planet is bombarded by 80 to 100 metric tons of space debris per day—but the impactors are mostly dust-size particles. However, whopper-size rocks do whiz about in space, and recently some have come uncomfortably close to our planet.

In its youth, Earth continuously was pelted by stones and vastly larger bodies. We've just learned, for example, that a huge asteroid about 19 kilometers (12 miles) wide smashed into Earth nearly 3.5 billion years ago, when the planet was just a billion years old.

We know. You're thinking, “Yeah, so what else is new?” Well, get this. Last June, a large asteroid just missed hitting Earth. The rock, labeled 2002MN, was about 50 to 120 meters (165 to 396 feet) wide and came within 120,000 kilometers (75,000 miles) of Earth—that's closer to us than the Moon. The scary note is that we didn't learn of the asteroid's existence until three days after its closest approach to Earth! Had 2002MN hit Earth, the impact could have affected an area as large as 2,080 square kilometers (about 800 square miles)—populated regions not excluded.

What's an innocent citizen of Earth to do about these extraterrestrial invaders? Read the next scoop!


One of the thousands of small planets that orbit the Sun, mostly in the region between Mars and Jupiter. Asteroids range in size from about one mile to several hundred miles in diameter.

Originating, located, or occurring outside Earth or its atmosphere.

planetary astronomer:
An expert in the scientific study and observation of planets in the universe beyond Earth.

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  1. What can be learned about Earth by studying rocks?
    [anno: Answers may vary but could include that studying rocks reveals what kind of minerals compose the surface of Earth, what kind of minerals are found beneath Earth's surface, and how Earth has changed over time.]
  2. What could asteroids teach scientists about other parts of the universe?
    [anno: Answers could include that scientists can learn about the composition of other planets by studying asteroids. Answers might also include that scientists can gain a better understanding of how space travel affects objects by studying the surface of asteroids.]
  3. How long ago did the asteroid that was 19 kilometers wide hit Earth?
    [anno: The asteroid hit Earth about 3.5 billion years ago.]
  4. How do you think scientists know that this asteroid hit Earth long ago?
    [anno: Answers may vary but could include that scientists have identified a crater associated with an asteroid impact.]