An asteroid called 2004 TP1 came within 13 LD of Earth on November 2 — LD stands for ‘lunar distance,’ and is the average distance between the Earth and the Moon (238,855 miles, or 384,401 kilometers). Asteroid 2004 RZ164 will come even closer, at 7 LD on December 8. Both objects are considered Potentially Hazardous Asteroids (PHAs, as acronym-obsessed scientists like to call them). That means they are larger than 100 meters in diameter and come too close to Earth for comfort.
653 Potentially Hazardous Asteroids are now known. We’ve discussed such objects as perhaps the most significant reason for building up a space-based infrastructure that could ward off a potential strike. A good place to track them is the NASA-sponsored site Spaceweather.com, which bills itself as ‘News and Information about the Sun-Earth Environment.’ The site likewise tracks solar wind conditions (currently moving at 493.7 kilometers per second, based on data transmitted from the Advanced Composition Explorer spacecraft at the L1 point between Earth and the Sun). Also available at Spaceweather.com: news of auroras, meteor showers, solar flares, and NOAA forecasts of the probability of geomagnetic storms.
