Cosmic Sweep

Many years ago, I read a fascinating book. In Chasing Dirt: The American Pursuit of Cleanliness (1996), Suellen Hoy examined the history of domestic notions of hygiene, and the technologies that led to changing standards. Something that stuck in my mind was the fact that lighting conditions in American homes from the 19th to the mid-20th Century had a direct effect on the amount of cleaning required, and hence on the whole industry of products – brooms, mops, dusters, cloths, vacuum cleaners, cleaning fluids – that were used to remove the natural accumulations of dust and dirt.

You didn’t need to clean spider webs out of corners when you couldn’t see them! With electric lighting, these dim corners were suddenly illuminated and subject to scrutiny. In brightly lit kitchens, surfaces had to be sparkling or the reputations of wives and mothers were at risk. Ironically, I accidentally dropped this book into the bath, staining it with brown water marks and turning its pages into ruffles.

By contrast, one of the big cleaning problems of the 21st Century is shrouded in darkness. Above our heads, millions of spacecraft and spacecraft fragments are orbiting Earth at an average speed of 7–8km per second. There are whole satellites and rocket bodies which no longer work, including the European Space Agency’s Envisat satellite (as big as two buses), down to minute submillimetre particles, detached as the harsh space environment gradually breaks down the spacecraft materials. 

The only light we have to observe these fragments is the Sun. At night, if you go out and watch for long enough, you might see a dot of light moving across the sky too fast to be a star or planet. It’s likely a Low Earth Orbit satellite. Satellites don’t have their own lights as aeroplanes do (and don’t flash in the same way). The reason they’re visible, and that they’re shining, is because they are high enough to reflect sunlight, even though the surface of Earth is in darkness. It’s quite fun to go satellite-spotting and connect with these outer space robots, to think they are now part of the same night sky that humans and their ancestors have contemplated for the last three million years.

In the contemporary world, a shooting star could easily be a piece of space junk burning up as it re-enters the atmosphere. As Billy Bragg sang in ‘A New England’:

I saw two shooting stars last night/I wished on them but they were only satellites/Is it wrong to wish on space hardware?

Personally, I like to think it’s right.

What we can’t see, though, are those millions of tiny fragments. It’s an invisible world beyond our senses. Most fragments can’t even be detected by optical, laser or radar imaging from Earth. We know they’re there, because sometimes spacecraft return to Earth and show evidence of bombardment by these tiny flecks. Like the dust building up in the nooks and crannies of a house lit only by candles and fire, these particles are out of sight, out of mind.

But like zombies, they refuse to die and go gently into that good night. They evolve into rogue orbits, roaming across the paths of the living satellites, threatening them with the impacts of a deadly force.

The first satellite, Sputnik 1, was launched by the Soviet Union in 1957. We have launched more and more objects into space every year since. When there were only a few human artefacts in space, the risks were not obvious. Soon, however, it became apparent that the rocket stages that delivered satellites to orbit and stayed aloft were prone to explode as the fuel left in them became unstable. The odd collision between spacecraft, the impacts of micrometeoroids, and the charged ionised gases in the space environment broke objects up and started the decay process. The lovely, shiny and very expensive satellites – that might, for example, deliver weather data accessed on smartphones around the world – run out of fuel or batteries and stop working. They turn into trash before our eyes. But like zombies, they refuse to die and go gently into that good night. They evolve into rogue orbits, roaming across the paths of the living satellites, threatening them with the impacts of a deadly force.

Recently … cosmic dust has been identified in house gutters in urban areas.

The fragments above about 10cm in size are the most deadly. They can cause some serious damage when they collide with functioning satellites. It’s widely recognised that something needs to be done to remove space junk from orbit and there have been many proposals for methods to do this, which usually involve altering the orbit of the junk fragments so that they get dragged back into the atmosphere to burn up. But what to do about the tiny grains of satellite decay, those minuscule particles that we can’t even see? And – even if we had the technology – how would we ensure that naturally occurring dust didn’t get swept up with the satellite dust in our clean-up efforts?

The solar system is full of cosmic and interplanetary dusts, left over from the formation of the planets billions of years ago. They swirl around us and drop through the atmosphere every day. According to one estimate, 40, 000 tonnes of dust fall to Earth each year. Scientists usually travel to the Antarctic to find cosmic dust grains because they’re hard to detect in environments already filled with dust or affected by industrial pollution. Recently, however, cosmic dust has been identified in house gutters in urban areas. Scientists are not concerned about this addition to household dust, though. Cosmic dust is intensely interesting and we study it to learn about the history and composition of the solar system.

The complex interplay of gravitational forces between the Moon and Earth has created stable locations called Lagrange points. In these interplanetary corners, cosmic dust accumulates in clouds, called Kordylewski clouds, that are very hard to see – their presence was only confirmed in 2018, although astronomers have suspected they exist since the 1960s. Dust particles get caught there and stay for a while before bouncing out again. As humans keep sending more spacecraft out into Earth orbit and to the Moon and Mars, I wonder if satellite dusts might eventually migrate to join the population of cosmic dust in the Kordylewski clouds.

The dust created by the space industry might be even further afield. In 1977, the United States launched two Voyager spacecraft to fly past the outer planets, never before visited, and continue out beyond the edge of the solar system. Perhaps as they soared through Earth orbit, they collected some grains of satellite dust on the way, and even more cosmic dust on their journey between the planets. One day, some future scientist might find the spacecraft light years deep into the galaxy. If they peel back the microscopic layers of dust that represent the journey, they’ll be able to look back in time to the early space age of the planet we call home.