Last week, asteroid 2012 DA14 flew relatively close to Earth. The asteroid is about 150 feet in diameter and passed about 17,000 miles above Earth's surface. NASA has just released a movie compiling 72 radar images of DA14 captured over 8 hours with the Deep Space Network antenna in Goldstone, California. I had no idea that DA14 was built in Minecraft. "NASA Releases Radar Movie of Asteroid 2012 DA14" (JPL)
The green circle in the lower right of this image marks the position of Earth's own trojan asteroid, discovered by researcher's involved with NASA's Wide-field Infrared Survey Explorer project.
What's a trojan asteroid? Glad you asked. The good news: It's not going to kill us all.
Trojans are asteroids that share an orbit with a planet near stable points in front of or behind the planet. Because they constantly lead or follow in the same orbit as the planet, they never can collide with it. In our solar system, Trojans also share orbits with Neptune, Mars and Jupiter. Two of Saturn's moons share orbits with Trojans.
Scientists had predicted Earth should have Trojans, but they have been difficult to find because they are relatively small and appear near the sun from Earth's point of view.
The team's hunt resulted in two Trojan candidates. One called 2010 TK7 was confirmed as an Earth Trojan after follow-up observations with the Canada-France-Hawaii Telescope on Mauna Kea in Hawaii.
The asteroid is roughly 1,000 feet (300 meters) in diameter. It has an unusual orbit that traces a complex motion near a stable point in the plane of Earth's orbit, although the asteroid also moves above and below the plane. The object is about 50 million miles (80 million kilometers) from Earth. The asteroid's orbit is well-defined and for at least the next 100 years, it will not come closer to Earth than 15 million miles (24 million kilometers).