|
A research team used a variety of methods to estimate the ages of asteroids ranging from 6 million up to 3 billion years. Accurate colour measurements for over 100 000 asteroids were obtained by using the Sloan Digital Sky Survey (SDSS), a UK-involved survey designed to map the entire visible universe.
The team found that there was a correlation between age and colour explaining a long-standing discrepancy between the colours of the most numerous meteorites, ordinary chondrites, and their presumed asteroid parents. Meteorites are pieces of asteroids that have fallen to Earth’s surface. Investigations of these celestial rocks give scientists an easy opportunity to look at the rocks currently in space.
David Nesvorny, a team member from the Southwest Research Institute, Boulder, USA, explains that “meteorites are gifts of the Solar System to scientists on Earth, pieces of asteroids delivered to their own backyard. The mystery is that the ordinary chondrite meteorites have a bluish colour relative to the reddish colour of the asteroids from which they were supposedly released.” This simple difference has always made identifying the parent asteroid very difficult.
About thirty years ago, a “space weathering” effect was proposed to explain this colour difference. Meteorites, whose surface is affected by their fall through Earth’s atmosphere, are usually studied in laboratories by observing there freshly cut and exposed interiors. The surface colour of asteroids may be changed after being exposed to solar and cosmic radiation and impacts from micrometeorites for billions of years.
The team discovered that asteroids get more red over time in exactly the right rate to explain the mystery of the colour difference between them and the ordinary chondrite meteorites. However, with this new evidence, the team has not been able to identify the exact mechanism that causes this space weathering. When the team refines their analysis, by obtaining more colours of the youngest-known asteroids, it will be possible to determine the age of any asteroid from its surface colour. They are currently searching for a space weathering effect on other types of asteroids in the Solar System.
Image: NASA.
This enhanced false colour image of asteroid, Ida with its small satellite Dactyl to the right, gives a vivid example of the effect of space weathering on asteroids. Blue regions on the asteroid tend to be associated with fresh young craters where subsurface material has been recently exposed to space. There are also blue regions associated with ridges and steep hills where surface material falls down during small “asteroid-quakes” to expose fresh surfaces. Red regions on the surface correspond to old craters and flat surfaces that have not been disturbed in a very long time.
The article is published in the current issue of the journal Nature.
More info: Nature
Related News
Hazardous Asteroid Found
Rosetta ready for icy adventure
Asteroid makes closest ever approach
|
