Can an Atomic Explosion Ignite a Chain Reaction of Deuterium in 3I/ATLAS?
One of the surprising anomalies of 3I/ATLAS is its exceedingly high fraction of deuterium, amounting to one deuterium (D) in 100 hydrogen (H) atoms in water (as reported here) and one deuterium in 30 hydrogen atoms in the organic molecule of methane (as reported here). The latter value of D/H fraction of 3.3% is a thousand times above the average cosmic value elsewhere in the Universe.
During the Manhattan Project, Edward Teller raised the speculative possibility that the fireball from an atomic bomb explosion might ignite the atmosphere by triggering a fusion reaction of nitrogen (14N) nuclei (as described here). In response, Hans Bethe calculated that ignition of the Earth’s atmosphere or the oceans was extremely unlikely because of radiative losses. A 1946 report, authored by Emil Konopinski, Cloyd Marvin Jr. and Edward Teller (accessible here), concluded that “whatever the temperature to which a section of the atmosphere may be heated, no self-propagating chain of nuclear reactions is likely to be started.”
In 1948 Konopinski and Teller published a paper (accessible here) with the first theoretical prediction for the fusion probability of two deuterium nuclei as bomb fuel. Their calculation motivated the development of the hydrogen bomb in two steps. First, the ignition of a plutonium bomb generates high temperature and density conditions, which in the second step trigger the fusion of deuterium fuel.
The fear of triggering a chain reaction remained a concern throughout the entire nuclear weapons test program, especially regarding the possibility that powerful underwater tests of hydrogen bombs might ignite oxygen (16O) atoms in water. Both theoretical and experimental data alleviated these concerns.
The nuclear age considerations led to the development of nuclear astrophysics, based on the realization that fusion of light elements powers stars. Deuterium fusion was of particular interest for the thermonuclear weapons community around Edward Teller, but also of great interest for understanding how low-mass stars shine.
Fast forward to a month ago: March 20, 2026, when a preprint (accessible here) reported that the interstellar object 3I/ATLAS shows an unexpectedly high deuterium abundance of D/H = (3.31 ± 0.34)% for methane. This discovery immediately raised the following question in my mind:
If an atomic bomb were to explode inside 3I/ATLAS, would it trigger a chain reaction of deuterium, generating a spark that ignites 3I/ATLAS into a gargantuan atomic bomb?
This is not a completely hypothetical question. Following the 1994 Shoemaker-Levy 9 comet impact on Jupiter, Edward Teller proposed to protect Earth from similar impacts by designing a nuclear explosive device equivalent to a gigaton of TNT, roughly the kinetic energy of a kilometer-diameter asteroid (as discussed here and here).
This brings me back to my question: If 3I/ATLAS was heading towards Earth and humanity decided to detonate Teller’s envisioned device at its center in order to decimate it, would the device ignite the deuterium-rich nucleus of 3I/ATLAS? If so, how much energy would be released in the resulting nuclear explosion of 3I/ATLAS?
Given that the minimum mass of 3I/ATLAS is 160 million metric tons (as calculated in a paper that I co-authored with Valentin Thoss and Andi Burkert, accessible here), the energy released by fusion of its entire deuterium content would be 10 teratons of TNT. This is about 200,000 times bigger than the largest nuclear explosion ever triggered on Earth — the Soviet Union’s Tsar Bomba, which released about 50 megatons of TNT on October 30, 1961.
If Teller’s nuclear device were to ignite a deuterium chain-reaction at the center of 3I/ATLAS, it would serve as a match that lights a fireball with 10,000 times more energy!
My simple back-of-the-envelope calculation before my morning jog at sunrise, indicates that radiative losses would not have saved us from a fusion chain reaction inside 3I/ATLAS.
For an opaque object at solid density like 3I/ATLAS, radiative losses occur at the surface before the object disintegrates. My calculations imply that the explosion triggered by Teller’s device would have disintegrated 3I/ATLAS over a hundredth of a second. In order for the radiative losses to compete with the huge energy released, the surface temperature would have had to rise up to a few million degrees. This, in turn, implies an even higher interior temperature — at which deuterium ignites. The energy released is sufficient to bring the fuel to a higher temperature before it has a chance to cool. For an explosion, in contrast to a steady source of energy, the released energy per unit time per unit volume must compensate for radiative cooling. If the initial spark ignites the fuel fast enough by raising the temperature to a high enough value so as to trigger a self-sustaining energy release, then a detonation wave forms and releases enough energy to burn fresh fuel as it propagates out. The released energy maintains the detonation front until it reaches the surface and destroys the entire object in the explosion. Exploding Teller’s device deep inside an interstellar object like 3I/ATLAS runs the risk of igniting a self-sustained D-D chain reaction and a gargantuan nuclear explosion in our cosmic backyard.
My preliminary estimate suggests that we should be careful in using Teller’s device for planetary defense. If we ever discover an interstellar object similar to 3I/ATLAS heading towards Earth, we will need to come up with an alternative, less explosive protective measure.
Here’s hoping that we will never face that risk.
ABOUT THE AUTHOR
Avi Loeb is the head of the Galileo Project, founding director of Harvard University’s — Black Hole Initiative, former director of the Institute for Theory and Computation at the Harvard-Smithsonian Center for Astrophysics (2005–2026), and the former chair of the astronomy department at Harvard University (2011–2020). He is a former member of the President’s Council of Advisors on Science and Technology and a former chair of the Board on Physics and Astronomy of the National Academies. He is the bestselling author of “Extraterrestrial: The First Sign of Intelligent Life Beyond Earth” and a co-author of the textbook “Life in the Cosmos”, both published in 2021. The paperback edition of his new book, titled “Interstellar”, was published in August 2024.
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