Most communications satellites circle the Earth in the Clarke Belt–i.e., in Geostationary Orbit 22,236 miles above Earth (about 1/10th the distance to the Moon). At that height, a satellite can orbit at a speed that matches Earth’s rotation, allowing the satellite to remain “stationary” relative to Earth’s spinning surface.
Recently, astronomers have discovered a new asteroid, 2012 DA14, orbiting the sun in a path that crosses Earth’s orbit. It’s about the size of half a soccer field. When asteroids are first discovered, their orbits cannot be discerned. It takes movement and additional observations to calculate an object’s trajectory. Astronomers now know its orbit. On February 15, 2013, it will approach Earth from the south and will pass, at its closest, to within 17,200 miles–5,000 miles closer than our communications satellites.
“This is a record-setting close approach,” according to NASA’s head of asteroid tracking, Don Yeomans. “Since regular sky surveys began in the 1990s, we’ve never seen an object this big get so close to Earth.”
Passing in mostly daylight, it will be difficult to see from the Western Hemisphere, although it might be visible for a short time to persons in Europe, Asia and Australia.
2012 DA14 is larger than a space shuttle and about 20% larger than the asteroid that is now believed to the responsible for the 1908 Tunguska explosion that leveled a forested area in Siberia nearly the size of Tokyo.
NASA Television will provide commentary starting at 2 p.m. EST on Friday, Feb. 15. You can watch it on your own television if you get NASA TV, or online here.
The asteroid will not hit Earth. But its passing is an unparalleled event that will draw lots of attention from Earth radar and tracking systems–a wonderful surprise for the day following St. Valentine’s Day.