NASA has released this graphic showing the orbits of all known Potentially Hazardous Asteroids (PHAs), that is, asteroids that are considered hazardous because they are fairly large (at least 460 feet or 140 meters in size), and because they follow orbits that pass close to Earth’s orbit (within 4.7 million miles or 7.5 million kilometers).
View larger. | This graphic shows the orbits of all the known Potentially Hazardous Asteroids (PHAs), numbering over 1,400 as of early 2013. Image via NASA
Astronomers have categorized more 1,400 PHAs as of early 2013.
Being classified as a PHA does not, of course, mean that an asteroid will impact the Earth. NASA is quick to point out:
None of these PHAs is a worrisome threat over the next hundred years.
Astronomers with NASA and other organizations do track these asteroids, continually refining what we know about their orbits so that more precise predictions can be made about their future close approaches and impact probabilities.
Deborah Byrd (asteroid 3505 Byrd) helps edit EarthSky.org and is a frequent host of EarthSky videos. Deborah created the EarthSky radio series in 1991 and founded EarthSky.org in 1994. Prior to that, she had worked for the University of Texas McDonald Observatory since 1976, and created and produced their Star Date radio series. She has won a galaxy of awards from the broadcasting and science communities, including having an asteroid named in her honor in 1990, a Public Service Award from the National Science Board in 2003, and the Education Prize from the American Astronomical Society in 2020. A science communicator and educator since 1976, Byrd believes in science as a force for good in the world and a vital tool for the 21st century. "Being an EarthSky editor is like hosting a big global party for cool nature-lovers," she says.
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