When you think about space, your mind is drawn to the very big - planets, stars and galaxies. But many of the universe’s secrets are hidden away in the stuff you can barely see: cosmic dust. Take our own Solar System. The gaps between the planets are peppered with tiny dust grains less than a tenth of a millimetre across. There’s enough of them that if you gathered up all the dust between the Sun and Jupiter you could fashion a sphere 25 kilometres (15.53 miles) across. On a clear night, far from city lights, you can even see sunlight reflecting off these particles in an effect called zodiacal light.
According to a study by scientists including Queen guitarist Brian May - who completed his PhD on zodiacal dust in 2007 - 70 per cent of this dust was deposited by comets during their long jaunts past the planets. Roughly 22 per cent comes from colliding asteroids, with the rest thrown into the Solar System from interstellar space. Scientists have long been keen to get their hands on some of this pristine cosmic dust in order to study it up close. In 1999 NASA launched the Stardust mission, and one of its aims was to return samples of cosmic dust to Earth. These returned home in 2006, and in 2014 scientists announced that they had found seven interplanetary dust particles among the haul.
But you don’t have to launch probes into space to get your hands on cosmic dust. As Earth orbits the Sun it regularly ploughs into streams of dust. These particles can strike Earth at speeds of almost 70 kilometres (43.5 miles) per second. Some of the larger grains are incinerated with such ferocity that we see them as meteors or shooting stars. Yet some of the dust survives the treacherous journey and reaches the ground.