Asteroid 433 Eros

Steven Dutch, Professor Emeritus, Natural and Applied Sciences, University of Wisconsin - Green Bay

Eros is one of the largest asteroids that can pass close to earth, so it was discovered early (1898) and has a fairly low number. It varies considerably in brightness as it rotates every 5-1/4 hours, so astronomers long ago figured out it must be longer than it is wide. It measures about 30 by 13 by 13 kilometers. Objects smaller than about 300 kilometers in diameter can be irregular because their gravity is too weak to pull the object into a spherical shape. Its surface gravity is about 1/1600 that of earth, meaning a 70-kilogram person would weigh about 4 grams on Eros. Its escape velocity is about 10 meters per second. Most people would not be able to jump free, but Olympic jumpers or pole vaulters might.

Eros was visited in 2000 by the NEAR mission (Near-Earth Asteroid Rendezvous). The mission marked a number of historic firsts. It was the first spacecraft to orbit an asteroid, the first spacecraft to orbit an irregular object (all other missions had orbited spherical planets or moons), the first mission to orbit an object whose mass was uncertain (making the process of entering orbit much trickier) and the first mission where orbital insertion was entirely automatic. Since its orbital velocity was only a few miles per hour, the spacecraft was moving slowly enough that it could be settled gently onto Eros. It landed on February 21, 2001, becoming the first spacecraft to land on an asteroid.

In the actual photos, the black shadows on the asteroid are indistinguishable from the black of space. The colored drawing uses slightly lighter colors to reveal the shape of the asteroid. In this view it is seen almost end-on.

Original Scene

(NASA image)

Possible Coloring

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Created 17 December 2007, Last Update 15 January 2020