Potential for Danger from Space

A WISE Survey of Nearby Space Rocks
There was a busy space probe out there called the Wide-field Infrared Survey Explorer (WISE, for short). As its name suggests, it was sensitive to infrared wavelengths of light and cataloged millions of objects before it went into hibernation in 2011. Many things radiate in the infrared, including some potentially hazardous asteroids (PHAs) that have the propensity to stray across Earth’s orbit from time to time. WISE has been sweeping its gaze across near-Earth space in search of these asteroids, which are detectable in infrared. Because the telescope detected the infrared light, or heat, of asteroids, it was able to pick up both light and dark objects, which gave astronomers a pretty good and pretty representative survey of what’s “out there”. The infrared data allowed them to make good measurements of the asteroids’ diameters and, when combined with visible light observations, how much sunlight they reflect.
NASA' NEOWISE survey finds more potentially hazardous asteroids in our planet's vicinity than previously thought. Courtesy NASA.
So, what is it about these PHAs that are so intriguing? First, they have the closest orbits to Earth’s of many asteroids. Some of them come within five million miles ...