Nuclear blast in space won't hit Earth directly. But what comes next will spell doom

A study has flagged a catastrophic risk if even one nuclear weapon is detonated in space. Countries are vying to place weapons in space, and some experts fear that a nuclear weapon might have already reached there. An explosion at a high enough altitude will knock out almost every satellite in low-Earth orbit. This has already happened in the past. The preprint paper is available on arXiv.

Researchers from the University of Wisconsin–Madison (UW) and Princeton University have said that even a less powerful detonation today will wreak havoc in low-Earth orbit. As part of the study, the researchers simulated a 1-megaton nuclear explosion 500 kilometres above the South Atlantic, where Earth's magnetic field is quite weak, leading to the South Atlantic Anomaly, where the effects of a blast are amplified. Radioactive particles are trapped in pockets of space and satellites move through this region.

"Electrons from radioactive fission-product decay became trapped in Earth's magnetic field, creating an artificial radiation belt that damaged satellites," first author Zach Petersen said. "Unlike the prompt burst, a trapped belt repeatedly exposes spacecraft as they pass through it. A comparable event today would occur in a much more densely populated orbital environment."

In the simulation, researchers found that 25 per cent of all satellites today (13,300) would be disabled one day after a nuclear blast in the region of the South Atlantic Anomaly. Seventy-eight per cent of satellites would be disabled by day three. The figure would rise to 98 per cent after a week, and 99.4 per cent by day 15.

Even if the satellites were given strengthened radiation protection, 99.3 per cent of all satellites would be disabled within 30 days. If a weaker 100-kiloton warhead were detonated, 99 per cent of satellites would be disabled within a year.

The detonations would also increase space debris after approximately 20 resulting collisions within the first two years. In 10 years, 3,900 new fragments of space junk will be formed orbiting Earth. "Continued collisions among long-lived objects are expected to sustain debris production beyond the simulated decade, with the possibility of a slow buildup and eventual runaway growth on century timescales," the study states.