Scientists don't agree on how many mass extinction events in earth's history were triggered by a space rock crashing into the planet's surface. However, most do agree that an asteroid collision 65 million years ago (among other things) was what brought an end to the age of dinosaurs. The outer planets Saturn and Jupiter protect us from many of these potential impacts, as was shown on July 20, when a huge scar appeared on Jupiter's surface, evidence of a comet impact. However, this is not always the case, and12,600 years ago North America was struck by a massiveobject that ended the ice age and gave rise to flood legendsaround the world.
Sometimes earth's gravity "captures" asteroids, so that they return regularly. There are also about 3,200 known cometsthat enter the inner solar system, and more appear yearly.Among the best-remembered recent comets is Hale-Bopp, which was easily visible to the naked eye for much of 1996 and 1997 and was one of the brightest comets of the 20th century. Halley's comet, which reappears about every 75 years, is perhaps the best-known comet. Cometsoriginate in a distant part of the solar system called the Kuiper Belt.
Will a comet or massive asteroid cause another extinctionevent on earth? When the Shoemaker-Levy comet crashed intoJupiter in 1994, it was thought to be a once-in-a-millenniumevent--but another massive impact took place just last week,and a bright spot on Venus may indicate that one of theinner planets also took a tremendous blow recently.
Unfortunately, unless an object reflects light, it cannot beseen by astronomers, and there are believed to be manylow-albedo objects present in the solar system. Neither theobject that struck Jupiter or the one that hit Venus (ifthat is the correct interpretation of the event on thatplanet) were seen before they struck.
When it comes to extinction, are we next? We'll find out pretty soon now.There's only ONE way to make sure unknowncountry doesn't become extinct: subscribe today! And if you have anything left at the end of the month, click on the "donate" tab on our homepage.
NOTE: This news story, previously published on our old site, will have any links removed.