Nuclear fusion technology may guide astronomers in their search for extraterrestrial civilizations.

Our own civilization serves as a prime example that the increasing demand for energy is inevitably tied to progress, and one can expect the same from a hypothetical extraterrestrial intelligent community. It is worth recalling the well-known scale of civilization development created by the Soviet astrophysicist Nikolai Kardashev: on this scale, the level of development is determined by the extent of energy resource utilization. We are not even on the lowest, first step of Kardashev's scale: to reach that level, we must learn to fully harness the energy of our planet. The second level involves utilizing the total energy of our star, while the third level is about mastering the galaxy.

One of the most crucial technologies for the future of humanity is the ability to control the process occurring within stars—nuclear fusion, which is the formation of heavier atomic nuclei from lighter ones, releasing immense energy in the process.

Astrophysicists from the universities of Washington and Arizona (USA) recently highlighted in an article available on the Cornell University preprint server that managed nuclear combustion of deuterium—a heavier form of hydrogen distinguished by the presence of an extra neutron in its nucleus—is considered the most promising. In the World Ocean, this isotope exists in relatively negligible amounts—0.0115 percent of all hydrogen on Earth—but in practical terms, this translates to billions of tons of yet-unused resource.

Researchers explained that they can successfully determine the ratio of deuterium to regular hydrogen in space by observing how these chemical elements reflect light: differences are visible in the spectrum. As a result, deuterium has been measured in the atmospheres of Mars and Venus, on the ice-covered moon of Saturn, Enceladus, and in the comets Hale-Bopp, Churyumov-Gerasimenko. It turns out that all this extraterrestrial water is significantly richer in heavy hydrogen than our own. In the interstellar medium, deuterium exists in minuscule amounts.

According to astronomers' calculations, if controlled nuclear fusion involving deuterium is actively utilized, its abundance on the planet will become even lower than in the interstellar medium, which could serve as a serious basis for suspecting the presence of a technologically advanced civilization on this planet. Moreover, such a signature could persist for hundreds of millions or even billions of years after the hypothetical civilization itself has vanished.