About 65 million years ago, a 10-kilometer-wide asteroid struck the Yucatan Peninsula and supposedly dispatched all the dinosaurs. Are we due for another strike?
Actually, small interstellar objects collide with the Earth quite frequently. The good news is that they are small enough to break up in the planet’s protective atmosphere to form “shooting stars” and do no harm. It’s only the larger ones that we need to worry about.
An example would be the binary asteroid Hermes
, which is made up of two massive components, each one between 300 and 450 meters (1,000~1,500 feet) wide. In 1937, it missed us by just 600,000 miles—slightly more than twice the distance to the moon.
But such visits are nothing new for Hermes. It approaches Earth’s orbit about once every 777 days, usually at a distance of about 18 moon lengths away. Scientists predict we are safe for at least another 100 years before the next “close call,” but just knowing Hermes is out there may give pause for thought.
Since Stone Age times, only a few really big impacts have occurred on the Earth’s surface. The meteorite that recently exploded over Russia, injuring 1,200 in February 2013, was only about 15 meters (49 feet) wide—tiny by cosmic terms.
By comparison, in 1908 an asteroid measuring 50 meters (164 feet) in diameter exploded above Siberia, mowing down trees for a 2,000 square kilometer radius and ending the lives of over a thousand reindeer.
A bit deeper in the past, a large asteroid broke up over the Chinese city of Ching-Yang in 1490. It was one of the most devastating impact events of modern history, killing an estimated 10,000 people.
Prior to that, one would have to travel back in time over 50,000 years to find evidence of a major strike—in this case an iron meteorite well over 30 meters (100 feet) in diameter that created the 1.2 kilometer (4,000-foot) Barringer meteorite crater in Arizona.
10 Biggest Known Hits
Craters found on Earth are the most obvious evidence of extraterrestrial strikes. Where are the largest? Here’s the rundown:
- Vredefort Crater – South Africa, 2 billion years ago. An estimated radius of 118 miles (190 kilometers), making it the world’s largest known impact structure.
- SudburyBasin– Canada, 1.8 billion years ago. An estimated diameter of 81 miles (130 kilometers).
- Acraman Crater– Australia, 580 million years ago. An estimated diameter of 56 miles (90 kilometers).
- Woodleigh Crater– Australia, 364 million years ago. An estimated diameter of 25 to 75 miles (40 to 120 kilometers).
- Manicouagan Crater– Canada, 364 million years ago. An estimated diameter of 62 miles (100 kilometers).
- Morokweng Crater– South Africa, 145 million years ago. This crater contains the fossilized remains of the meteorite that created it.
- Kara Crater – Russia, 70.3 million years ago. It actually consists of two adjacent craters: the Kara and the Ust-Kara crater.
- Chicxulub Crater– Mexico, 65 million years ago. An estimated diameter of 106 to 186 miles (170 to 300 kilometers).
- Popigai Crater– Russia, 35.7 million years ago. Russian scientists claim that this crater site contains trillions of carats of diamonds, making it one of the largest diamond deposits in the world. These diamonds have been referred to as “impact diamonds.”
- Chesapeake Bay Crater – United States, 35 million years ago. An estimated diameter of 53 miles (85 kilometers).
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