Astronomy for all
Friday April 9th 2010

A look at some asteroids

So what is an asteroid? The term comes with some confusion as the distinction between asteroids, comets, meteoroids, and (TNO) Trans-Neptunian objects are somewhat ill-defined, and then there are minor planets, the preferred term by the International Astronomical Union until 2006, when the term “small Solar System body” (SSSB) was introduced to cover both minor planets and comets. The 2006 definition of SSSB says that they “include most of the Solar System asteroids, most Trans-Neptunian Objects (TNOs), comets, and other small bodies”.

Regardless of all this terminology confusion, most people have some concept of whatthey look like. Did you know however that asteroids appear to be up to 50% empty space, suggesting that they could be collections of rubble with no solid core. So lets take a quick look at a few of them.

Itokawa, a dusty asteroid (Credit: JAXA)

The asteroid was discovered in 1998 by the LINEAR project, and given the provisional designation 1998 SF36. In 2000, it was selected as the target of Japan’s Hayabusa mission. Soon thereafter, it was officially named after Hideo Itokawa, a Japanese rocket scientist.

This image of near-Earth asteroid 433 Eros reveals that its ancient surface has been scarred by numerous collisions with other small objects. Image credit: NASA/JPL/JHUAPL

Eros was one of the first asteroids to be visited by a spacecraft, and the first to be orbited and soft-landed on. NASA spacecraft NEAR Shoemaker entered orbit around Eros in 2000, and came to rest on its surface in 2001.

Galileo image of 243 Ida. The tiny dot to the right is its moon, Dactyl.

Ida was visited in 1993 by the Jupiter-bound space probe Galileo. Its encounters of the asteroids Gaspra and Ida were secondary to the Jupiter mission. These were selected as targets in response to a new NASA policy directing mission planners to consider asteroid flybys for all spacecraft crossing the belt. No prior missions had attempted such a flyby. Galileo was launched into orbit by the Space Shuttle Atlantis mission STS-34 on 18 October 1989. Changing Galileo’s trajectory to approach Ida required that it consume 34 kg (75 lb) of propellant. Mission planners delayed the decision to attempt a flyby until they were certain that this would leave the spacecraft enough propellant to complete its Jupiter mission.


This is a NASA Hubble Space Telescope color image of Ceres, the largest object in the asteroid belt.

Astronomers enhanced the sharpness in these Advanced Camera for Surveys images to bring out features on Ceres’ surface, including brighter and darker regions that could be asteroid impact features. The observations were made in visible and ultraviolet light between December 2003 and January 2004.

For more images of asteroids visit the Nasa Photo Journal.

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