Today is not a good day for the anxious among us. Two small asteroids — two in twelve hours — are passing the earth, both coming within the moon's orbit, one of them whipping by about 49,000 miles away.
In a spirit of calm, we ought to point out that NASA says close calls like these happen, on average, almost daily. The difference is that usually we never know. These two objects were both spotted Sunday by the Catalina Sky Survey at the University of Arizona.
–Asteroid 2010 RX30 is estimated to be 32 to 65 feet in size (10-20 meters) and passed within 154,000 miles of Earth at 5:51 a.m. EDT this morning. (The moon, by comparison, is 2,200 miles in diameter and respectfully stays about 240,000 miles away.)
–Asteroid 2010 RF12, about 20-45 feet in maximum width (6-14 meters), is passing within approximately 49,088 miles of us at 5:12 p.m. EDT. That’s a fifth as far away as the moon.
(NASA/JPL plot of asteroids' paths. Click to enlarge.)
A decade ago, this was the stuff of movies — think "Armageddon" and "Deep Impact" — but one of the more memorable lines from back then was that the planet would be whacked by something "the size of Texas." Asteroids the size of today's passersby enter the earth's atmosphere about once a decade, mostly harmlessly.
Of course, every now and then — remember the theory about the death of the dinosaurs — something hits us that is not harmless. The object believed to have ended the Cretaceous period is estimated to have been about six miles across. And that’s why the astronomers in Arizona didn’t have much of a Labor Day weekend.Update: Wayne Farley asks a good question: How quickly are either of these objects moving? The answer, according to the Near Earth Object program at NASA, is a maximum of about 6 km/second –about 13,400 mph — for 2010 RF12 and 10 km/second — 22,370 mph — for 2010 RX30, relative to us. (For comparison, a spacecraft in low earth orbit moves at about 17,000 mph relative to the earth's surface.) If you want to have some fun, the Jet Propulsion Lab has an interactive graphic of the orbit of 2010 RF12 and other objects HERE.
(Top: Asteroid Ida, imaged by the Galileo spacecraft on the way to Jupiter in August 1993. Click to enlarge. Courtesy NASA/JPL.)