It’s easy to compare the space junk problem to climate change. Human activities leave too many dead satellites and fragments of machinery discarded in Earth orbit. If left unchecked, space junk could pose significant problems for future generations — rendering access to space increasingly difficult, or at worst, impossible.
Yet the two may come to be linked. Our planet’s atmosphere naturally pulls orbiting debris downward and incinerates it in the thicker lower atmosphere, but increasing carbon dioxide levels are lowering the density of the upper atmosphere, which may diminish this effect. A study presented last month at the European Conference on Space Debris says that the problem has been underestimated, and that the amount of space junk in orbit could, in a worst-case scenario, increase 50 times by 2100.
“The numbers took us by surprise,” said Hugh Lewis, a space debris expert from the University of Southampton in England and a co-author on the paper, which will be submitted for peer review in the coming months. “There is genuine cause for alarm.”
Our atmosphere is a useful ally in clearing up space junk. Collisions with its molecules cause drag, pulling objects back into the atmosphere. Below 300 miles above the surface, most objects will naturally decay into the thicker lower atmosphere and burn up in less than 10 years.
rerelease infrared radiation after absorbing it from the sun, which is then trapped by the thick atmosphere as heat. But above 60 miles where the atmosphere is thinner, the opposite is true. “There’s nothing to recapture that energy,” said Matthew Brown, also from the University of Southampton and the paper’s lead author. “So it gets lost into space.”
21 percent of its density because of rising carbon dioxide levels. By 2100, if carbon dioxide levels double their current levels — in line with the worst-case scenario assessment by the Intergovernmental Panel on Climate Change — that number could rise to 80 percent.
For space junk, the implications are stark. More than 2,500 objects larger than four inches in size currently orbit at or below an altitude of 250 miles. In the worst-case scenario, increased orbital lifetimes of up to 40 years would mean fewer items are dragged into the lower atmosphere. Objects at this altitude would proliferate by 50 times to about 125,000.
Even in a best-case scenario, where carbon dioxide levels stabilize or even reverse, the amount of space junk would still be expected to double. Mr. Brown thinks a more probable outcome is somewhere in between, perhaps a 10 or 20 times increase.