Astronomers observing inbound asteroid 2011 MD found that their calculations were a little off. The asteroid, which measures 15 feet by 60 feet wide, is what is known as a PHA (Potentially Hazardous Asteroid), and was headed toward Earth. It is just one of many that NASA's Near Earth Objects Observation Program regularly tracks. But this particular massive space rock was scheduled to arrive Monday morning and pass about 7,500 miles above the Earth's surface. It did neither.
Getting calculations wrong by a degree or two could mean the difference between a fly-by and a devastating impact. This time, the calculations erred in the Earth's favor...
2011 MD arrived as planned, but not where or when astronomers first suspected, according to the Associated Press. Updated information put the asteroid passing by the Earth at just after noon (1:00 p.m. EDT). It did not come as close as they thought it would, either. Calculations also found the asteroid passing by the Earth at a distance of 7,600 miles away.
Although science fiction movies and television shows thrill us with the horrors of an impending asteroid-based cosmic hit job (think: "Armageddon" and "Deep Impact"), shelving the thought of an apocalyptic run-in with a gigantic space rock is a distinct possibility. It is theorized -- and subsequent data and studies have reinforced the theory -- that just such a collision occurred 65 million years ago, slamming into the Gulf of Mexico region and forming the Chixulub Crater. It is believed to be the major cause of the extinction of the dinosaurs and the mass die-off at the end of the Cretaceous Period, forming what scientists call the K-T boundary, the geologic boundary that exists between the Cretaceous and Tertiary Periods of geologic time.
CNN reported in 2010 that researchers reaffirmed the 1980 theory, their findings from a Chixulub Crater which was discovered in 1991, indicating that an asteroid 6 miles in diameter slammed into the Earth at 43,000 miles per hour. The resulting crater measured 24 miles deep and 125 miles wide. It is estimated that the asteroid hit with an impact comparable to a blast created by the detonation of 100 million megatons of TNT.
Species-ending impacts aside, the New Earth Objects Program currently tracks nearly 800 PHAs.
2011 MD was just the latest near miss-by an asteroid. In fact, a smaller asteroid passed even closer to the Earth in January -- just 3,400 miles out. In just the last week, the program tracked 10 PHAs, most passing outside of an Astronomical Unit (nearly 93 million miles) from the planet. This includes 65909 (1998 FH12), an asteroid that measures a quarter-mile by a half-mile wide, which passed by on June 23.