This animation from the Arecibo Observatory in Puerto Rico plots the positions of all the known asteroids in the solar system in 1980, and adds new ones as they are discovered. The pace and patterns of asteroid discovery give a neat visual illustration of the history of solar system exploration.
New asteroids appear in flashes of white, to make them easy to pick out. The final color codes for how close the object comes to Earth: Asteroids that cross Earth’s orbit are shown in red, “Earth approachers” that come to 1.3 times the Earth-sun distance are yellow, and all others are green. The bunches of new asteroids follow Earth in its orbit, usually in the region directly opposite the sun (that is, in the Earth’s night sky). Some clusters appear on the line between Earth and Jupiter, the side effects of surveys looking for Jovian moons.
In the mid-1990s, the pace of discovery picks up, showing the results of automated sky surveys. By 2001, the area just outside the orbit of Mars is filled in by a bright green ring of asteroids, and it keeps getting denser.
The beginning of 2010 brings a new pattern of discovery, with new asteroids fanning out on either side of the Earth. This new pattern is thanks to the Widefield Infrared Survey Explorer (WISE), an infrared space telescope that is expected to find hundreds of new asteroids by seeking their heat rather than their light.
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