Composite of 9 pictures showing mulitiple Geminid meteors, including a -6 magnitude fireball, photographed from a mountainside above Coal Creek Canyon, Colorado. Each flash represents a grain or pebble of the asteroid Phaethon burning up in our atmosphere. Credit: Dr. Richard Keen
This morning two small asteroids passed harmlessly by Earth at distances of just 174,000 and 292,000 miles. 2012 XP134, the more distant and measuring 42 feet across, whizzed by at 8 a.m. (CST) and 40-foot -wide 2012 XL134 two hours later. While some may take the sign of so many Earth-approaching asteroids as a bad omen, it’s all good news in my view.
NASA estimates there are a total of about 10 million near-Earth asteroids in the 10-meter (32 feet) range with an expected impact rate of one every 10 years. If you up the size to 30-meters (100 feet), there are 1.3 million objects with an impact rate of one every 200 years. Objects this size are still too small to gouge a crater and cause significant damage on the ground. Most would be expected to fragment in an airburst and possibly drop meteorites along their entry paths.
This chart shows how data from NASA’s Wide-field Infrared Survey Explorer, or WISE, has led to revisions in the estimated population of near-Earth asteroids (NEAs). The infrared-sensing telescope performed the most accurate survey to date of NEAs. Small objects found weekly number in the millions. Click photo to learn more about asteroid numbers. Credit: NASA
With numbers like these, it’s no surprise that Earth-shaving asteroids are discovered routinely. According to Donald Yeomans, manager of NASA’s Near-Earth Object Program Office, asteroid search programs find about 20 every week. In tomorrow’s blog, I’ll be reviewing his brand new book on the topic.
I’m glad all these good people are watching out for flying rocks. Not only does it mean we humans are becoming more knowledgeable about our surroundings, but knowing their orbits allows us to forecast when one of them might pose a danger in the future. This, we hope, will stir us to devise solutions to avoid a potential disaster. In 1990 there were only 134 Earth-approaching asteroids known; as of mid-2012 that number is somewhere around 9,000 and rising every week. Wouldn’t you rather know what’s coming than be in the dark?
Flyby images of the 3-mile long asteroid Toutatis taken by the Chinese Chang ‘e 2 spacecraft earlier this week. Its odd shape might be the result of two separate asteroid fragments that stuck together after a gentle collision. Click for larger version. Credit: SASTIND via Weibo / UMSF
Many of us got to experience first hand this week what happens when minute pieces of an asteroid strike Earth’s atmosphere – a beautiful meteor shower! Thurday night’s Geminids originate from dust and small pebbles released from the 3.1 mile long asteroid 3200 Phaethon. Two nights prior to the Geminid peak, the largest near-Earth asteroid 3179 Toutatis, also about 3 miles long, passed some 3.4 million miles from the planet.
64-frame movie showing Toutatis tumbling through space only 4.3 million miles from Earth on Dec. 12-13. Credit: NASA/Goldstone radar
While Phaethon’s too faint for most amateur telescopes, Toutatis remains bright as it slowly travels through the constellations Cetus and Aries this month. I watched this star-mimic amble through my telescope field of view Thursday night while trying to appreciate exactly what I was looking at. Fortunately the Chinese and NASA’s Goldstone radar provided some help.
A cropped version of picture sequence shows a clearer view of the asteroid’s surface. The bumps could be piles of boulders. Credit: Chinese National Space Agency
As the spacecraft flew by the bizarre-shaped Toutatis at the relative speed of 24,000 mph, it snapped a series of approach pictures. Higher resolution images will soon be released, but these are clear enough to see what appear to be boulder piles strewn about the surface as well as shallow craters. We live in wonderful times.
