NASA surveys asteroids to see which are potentially hazardous
Orbit Comparison: This diagram illustrates the differences between orbits of a typical near-Earth asteroid (blue) and a potentially hazardous asteroid, or PHA (orange). PHAs are a subset of the near-Earth asteroids (NEAs). They have the closest orbits to Earth’s orbit, coming within 5 million miles (about 8 million kilometers), and they are large enough to survive passage through Earth’s atmosphere and cause damage on a regional, or greater, scale. JPL/NASA public domain image.
NASA conducted a survey to determine which asteroids are potentially hazardous to earth. NASA scientists discovered that, in comparison with near-earth asteroids, the potentially hazardous asteroids are brighter and therefore more likely composed of hard rock, such as granite, or metal.
The potentially hazardous asteroids pass closer to earth than near-earth asteroids and are considered large enough to survive passage through the earth’s atmosphere. That’s why they’re labelled potentially hazardous.
Asteroids with lower-inclination orbits would be more likely to encounter Earth and would be easier to reach. The results therefore suggest more near-Earth objects might be available for future robotic or human missions.
None of the potentially hazardous asteroids are slated to hit earth on December 21, 2012, as far as I can tell. It appears that the end of the world on December 21, 2012 will not occur because of an asteroid impact with earth. However, near-earth asteroid 2007 PA8 did pass within 17 times the distance between the earth and moon in November (last month).
Carol Chapman, author End of the World 2012 EBook, Book, and Movie
