Is dust the source of life on Earth?
Philip Pullman fans will be familiar with the fictionalised idea of dust.
The particles play a key role in the author's popular His Dark Materials series.
But a new University of Edinburgh study suggests it might really be the source of life on earth.
Fast flowing streams of interplanetary dust are continually entering our planet's atmosphere, travelling at up to 70 km per second.
According to the study, this dust could collide with particles in the atmosphere and propel them with enough energy to escape into space, and potentially reach other planets.
Some of these particles might contain living organisms, possibly leading to an interplanetary transfer of life.
This process could also work in reverse, with dust delivering organisms from other planets to earth.
Some bacteria, plants and small animals called tardigrades can survive in space.
The study was led by Prof Arjun Berera from the University of Edinburgh's school of physics and astronomy.
He said: "The proposition that space dust collisions could propel organisms over enormous distances between planets raises some exciting prospects of how life and the atmospheres of planets originated. The streaming of fast space dust is found throughout planetary systems and could be a common factor in proliferating life."
It was previously thought that large asteroid impacts were the only way for life to be transferred between planets.