Dust: it gets everywhere

As we speak dust storms are ravaging parts of northwest China turning the skies dark and closing down schools and factories. According to Wired Science China's dust storm season lasts from March to May each year costing the superpower dearly in terms of both its economy and human health; with respiratory conditions triggered or exasperated by the melee of particles. So where does all this dust come from?

A lot of it probably comes from the Bodele Depression in Chad, Oxford researchers have discovered, where a combination of wind power and surface sediments see a low-level 'jet' of dust fired into Earth's atmosphere. The Bodele is, they believe, our planet's largest source of dust. But of course dust isn't just in our backyard, it's a feature of other planets too: Early observations of Mars showed marked seasonal changes in how the planet reflects light (its albedo) but it wasn't until 1971, when the Mariner 9 probe touched down in the middle of an almighty dust storm, that scientists had hard evidence that dust was what was causing it to dim. Scientists have found that dust accumulates in similar formations on the Earth and Mars (compare these cresent-shaped 'barchan' dunes on Earth and Mars). Such comparisons are useful because they suggest that many of the same climate processes are at work on both planets - and the Martian climate could teach us many lessons about climate change on Earth. But planets hardly have a monopoly on dust: it peppers the space between stars and galaxies making up around 1 per cent of the interstellar medium - the cosmic 'haze' (of which the other 99 per cent is gas) that can hide black holes and other interesting astronomical objects from astronomers.

Yet while dust can pose problems for astronomers it also plays a crucial role in the evolution of galaxies, with the presence of dust being vital for star formation. That's why astronomers are so excited about finding overlapping galaxies which enable them to study the dust in different galactic systems and perhaps understand how stars and solar systems like our own are formed. Maybe Ole Reed in Gladiator was right: We mortals are but shadows and dust.

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