With the sun-drenched days we’ve had of late, chances are you’ve been enjoying the glorious weather and topping up your tan; and you aren’t the only one. Research published in Nature by a team at the European Southern Observatory (ESO) suggests that, as well as bronzing your skin, the Sun colours the surface of asteroids too.
But unlike us, the hue of the asteroid is honed not by UV light but by particles streaming away from the Sun in the solar wind. This ionised surge of matter from the Sun peppers the surface of the asteroid in so-called ‘space weathering’, turning the surface of the asteroid a distinctive red colour.
What has surprised astronomers, using ground based telescopes such as the Very Large Telescope (VLT) in Chile, is the shear speed at which these asteroids seem to ‘tan’. Studying collisions between asteroids, and examining the freshly exposed surfaces of the resulting fragments, the team discovered that this tanning process takes only a million years. That may sound a lot to a very short lived species such as ourselves, but taken in the context of the age of the solar system, it is the equivalent of five days in the lifespan of a seventy year old human.
This rapid timescale has led to better understanding of the so called Near Earth Asteroids (NEA’s), which Jacob talked about recently. Some of these space rocks, the ones mostly likely to worry us about possible impacts, don’t appear to exhibit this reddening. This could suggest that they are less than a million years old and caused by asteroid-on-asteroid collisions that are more frequent than previously thought. However, the team suggest their apparent ‘freshness’ is due to gravitational interactions with planets effectively wiping the weathered red dust off the surface, therefore the asteroids are much older.
Vernazza, P., Binzel, R., Rossi, A., Fulchignoni, M., & Birlan, M. (2009). Solar wind as the origin of rapid reddening of asteroid surfaces Nature, 458 (7241), 993-995 DOI: 10.1038/nature07956