Does the space junk orbiting Earth have any effect on the amount of solar energy reaching the surface of our planet, either by absorbing or reflecting it?
Richard Lucas, Camberley, Surrey, UK
Since 1957, more than 5000 launches have led to in excess of 22,000 tracked objects in orbit around Earth. But only a minority are working satellites. The rest, including satellites no longer serving a useful purpose, are debris.
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Many derelict craft have broken up, generating an 1 centimetre and 10 centimetres across, and a staggering 128 million between 1 millimetre and 1 centimetre in size. All of these will absorb or reflect solar radiation to an extent, depending on colour and reflectivity.
Travelling at speeds in the order of tens of thousands of kilometres per hour, even these tiny bits of junk present a danger to satellites. The International Space Station was damaged in August 2018, though it isn’t yet clear whether this was caused by flying debris.
But despite the large amount of junk, the total number of pieces in orbit is relatively small compared with the area of the planet that is exposed to solar radiation. Also, since all of these bits are in orbit around the planet, less than half of them will be between the sun and Earth at any time. So while space junk will have an impact on incoming solar energy, that effect is vanishingly small.
Eric Kvaalen, Les Essarts-le-Roi, France
It has a tiny effect. Although it isn’t clear in which direction the light is reflected, it is such a small amount as to be totally negligible. One gets the impression from some articles that there is so much junk up there that it is like a swarm of gnats, but, in fact, the total mass – and total cross-sectional area – is small.
Mike Follows, Sutton Coldfield, West Midlands, UK
Satellites vary greatly in size, but if we assume that the average cross section is 5 square metres, this means that on Earth they could all be parked in a field measuring about 0.025 square kilometres.
So in space, they would intercept only a tiny fraction of 1 per cent of the sunlight that is heading for the planet, provided they are between the sun and Earth, of course.
In the section of space out to 2000 kilometres above Earth’s surface, there is less than one piece of space debris larger than 1 cubic millimetre for every 10,000 cubic kilometres of space. Though this equates to a huge number of pieces of debris, only around 34,000 exceed 10 centimetres across.
The effect of space debris on solar energy reaching the planet would increase if there were a chain reaction of collisions, in which one piece of debris hit a satellite, breaking it up into thousands of pieces that hit other satellites and then did the same again. Yet even if this happened, it wouldn’t have a significant impact on the amount of sunlight reaching us.
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