Top Document: [sci.astro] Solar System (Astronomy Frequently Asked Questions) (5/9) Previous Document: E.17.2 What can we do about avoiding impacts? Next Document: E.18 What's the difference between meteoroids, meteors, and meteorites? See reader questions & answers on this topic! - Help others by sharing your knowledge These such questions typically occur after a news report of a future close encounter between the Earth and an asteroid. To date, all such reports have resulted from (1) Astronomers did not yet know well enough the orbit of a newly-discovered asteroid to say with any certainty that it would not hit the Earth; (2) Reporters not checking their stories or misunderstanding what they were told; or (3) both. Objects that can potentially come close to the Earth are referred to as Near-Earth Objects (NEOs). The International Astronomical Union maintains lists of such objects. About 100 asteroids are classified as "Potentially Hazardous Asteroids" (PHAs), at <URL:http://cfa-www.harvard.edu/iau/lists/Dangerous.html>; they all have a projected closest distance to Earth of less than 0.05 AU (7.5 million km). A list of closest approaches to the Earth by PHAs between 1999 and 2099 is available at <URL:http://cfa-www.harvard.edu/iau/lists/PHACloseApp.html>. A list of moderately close (to within 0.2 AU) approaches to the Earth by asteroids and comets between 1999 and 2032 is available at <URL:http://cfa-www.harvard.edu/iau/lists/CloseApp.html>. At the moment, NONE of these encounters is thought to pose a serious risk. The "potential hazard" of PHAs lies in their orbits and the perturbations on those orbits from the planets and the Moon currently not being known with sufficient accuracy to completely exclude the possibility of a collision, but, generally, labeling these asteroids as PHAs is erring on the side of extreme caution. It is not worth losing any sleep over them. User Contributions:Top Document: [sci.astro] Solar System (Astronomy Frequently Asked Questions) (5/9) Previous Document: E.17.2 What can we do about avoiding impacts? Next Document: E.18 What's the difference between meteoroids, meteors, and meteorites? Part0 - Part1 - Part2 - Part3 - Part4 - Part5 - Part6 - Part7 - Part8 - Single Page [ Usenet FAQs | Web FAQs | Documents | RFC Index ] Send corrections/additions to the FAQ Maintainer: jlazio@patriot.net
Last Update March 27 2014 @ 02:11 PM
|
Comment about this article, ask questions, or add new information about this topic: