NASA's Spitzer Space Telescope has revealed a colourful mixed bunch of asteroids, with a surprisingly wide array of compositions, much like an assorted box of candies.

Some are dark and dull; others are shiny and bright. The findings are helping astronomers better understand near-Earth objects as a whole-a population whose physical properties are not well known.

"These rocks are teaching us about the places they come from," said David Trilling at Northern Arizona University.

Spitzer is helping to gather more accurate estimates of asteroids' compositions and sizes than what is possible with visible-light alone.

"Our data will tell us more about the population, and how it changes from one object to the next. This information could be used to help plan possible future space missions to study a near-Earth object," Trilling said.

Since asteroid surfaces become darker with time due to exposure to solar radiation, the presence of lighter, shinier surfaces for some asteroids may indicate that they are relatively young.

A greater degree of diversity indicates that some may have come from the main belt between Mars and Jupiter, and others could come from farther out in the solar system.

Future research may reveal new clues about how the cosmic objects might have dotted our young planet with water and organics-ingredients needed to jump-start life.

The research appears in the September issue of Astronomical Journal. (ANI)