Comet's heart may have struck Earth

Bright lights that suddenly streak across the night sky with an accompanying boom tend to elicit a flurry of phone calls to local police departments.

These rare events aren't typically wayward missiles, or satellite debris (as was thought when one such streak recently lit up the skies over Texas), or alien invasions. But they do come from outer space.

Scientists aptly call the objects fireballs because they are the brightest meteors, or "shooting stars," that fall to Earth.
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