It's raining cosmic dust

For the past 30,000 years, the Earth has been hit by a steady rain of cosmic dust particles, according to new research published in the latest edition of the journal Science. Large amounts (around 40,000 tonnes) of extraterrestrial matter hit our planet every year, but until ...

For the past 30,000 years, the Earth has been hit by a steady rain of cosmic dust particles, according to new research published in the latest edition of the journal Science.

Large amounts (around 40,000 tonnes) of extraterrestrial matter hit our planet every year, but until now it has been unclear whether the levels of cosmic dust arriving on Earth have varied over time or remained constant.

To answer this question, researchers from the Alfred Wegener Institute in Germany and Columbia University in the US looked at dust trapped in Antarctic ice cores dating back 30,000 years. Dust particles with an extraterrestrial origin were identified by their high levels of the rare helium isotope 3He. 'During its journey through space, the cosmic dust is charged with helium atoms by the solar wind. At this point they are highly enriched with the rare helium isotope 3He,' explained Dr Hubertus Fischer of the Alfred Wegener Institute. 'Cosmic dust particles in the size of a few micrometres enter the Earth's atmosphere unharmed and carry their helium load unchanged to the Earth's surface.'

Due to the high temporal resolution of ice cores, the scientists were able to determine, with precision, changes in dust levels over time. Their results suggest that at least for the time period studied, there was little variation in the levels of cosmic dust reaching the Earth.

However, while the levels of cosmic dust in the ice remained constant over time, the same cannot be said for terrestrial dust. Terrestrial dust has a higher level of the helium isotope 4He, and measurements of 4He in the ice suggest that the terrestrial dust landing in the Antarctic now is different from the terrestrial dust that got there during the last ice age.

'This may be due to mineral dust originating from different regional sources, or to changes in weathering, the process responsible for production of dust,' said Dr Gisela Winckler of Columbia University.

The researchers now aim to look at variations in cosmic dust levels going further back in time; according to Dr Fischer, there are ice core records going back 300,000 years. They also want to look more closely at the origins of terrestrial dust landing on Antarctica.

Data for the study were collected within the European Project for Ice Coring in Antarctica (EPICA), funded under the EU's Fifth Framework Programme (FP5).