A study found that small satellites can verify whether nuclear weapons are deployed in Earth orbit. The findings are drawing attention because they could be used to verify compliance with the Outer Space Treaty, which bans placing nuclear weapons in space.
A research team led by Areg Danagoulian of the Massachusetts Institute of Technology (MIT) said on the 9th in the international journal Nature that satellites carrying nuclear weapons can emit distinct neutron signals as they interact with their surroundings, and that these can be detected by small CubeSats.
The Outer Space Treaty, a core instrument of international space law established in 1967, has been ratified by 118 countries, including the United States, China and Russia. The treaty bans placing nuclear weapons or weapons of mass destruction in Earth orbit. If a nuclear weapon were to detonate in space, most low-Earth-orbit satellites could be damaged, severely impacting Earth's core infrastructure, including communications, navigation and weather observation. But there has been no practical way to determine whether a given satellite is carrying a nuclear weapon.
The researchers reasoned that when uranium inside a nuclear weapon collides with protons trapped in Earth's magnetic field, the uranium nuclei could fission and emit neutrons. Modeling predicted that if a satellite were assumed to carry a nuclear weapon containing a 95-kilogram lump of uranium, roughly 30 million neutrons per second could be produced.
According to the team's calculations, even a 9U CubeSat (1U is 10 cm by 10 cm by 10 cm) built with commercial off-the-shelf parts could detect this signal. CubeSats are small satellites made by combining multiple cube-shaped modules, and because their size and expense are relatively small, they are often used by universities, research institutions and private corporations.
In modeling based on a hypothetical scenario, if there were a satellite in low Earth orbit carrying a nuclear weapon, a CubeSat observing for about a week from roughly 4 kilometers away could identify a thermonuclear signal. A thermonuclear weapon, often called a hydrogen bomb, is a powerful type of nuclear weapon.
However, the researchers noted, "Additional verification is needed to apply this method in the actual space environment," adding, "This result is an important starting point for developing technologies to verify nuclear weapons in space."
Angela Di Fulvio, a professor at the University of Illinois Urbana-Champaign who was not involved in the study, said, "We need to analyze precisely whether satellites can maintain close distances and the extent of background radiation produced by solar particles or cosmic rays," adding, "Because the actual configuration of nuclear weapons is not public, additional research in an appropriate security environment is also needed to identify the neutron characteristics that could be emitted by nuclear weapons."
References
Nature (2026), DOI: https://doi.org/10.1038/s41586-026-10783-2
Nature (2026), DOI: https://doi.org/10.1038/d41586-026-01944-4