From John Brandenburg, Jacksonville, Oregon, US
As a contributor to the documentary Blue Planet Red, I would like to address the criticism in Simon Ings’s review that xenon-129’s presence in the Martian atmosphere implies ancient nuclear conflict only if you ignore the well-understood process by which a now-extinct isotope, iodine-129, would have decayed to xenon-129 in Mars’s rapidly cooling lithosphere (11 October, p 32).
When Mars and Earth formed 4.5 billion years ago, they contained both iodine-129, source of xenon-129, and plutonium-244, source of xenon-132. The half-lives of both isotopes are comparable in geologic timescales and their decay products should have both outgassed by now.
On Earth, these isotopes are approximately equal in abundance in the atmosphere, but on Mars, there is 2.5 times more xenon-129 than xenon-132. The mystery is why the iodine-129 decay product shows up, but there is less of the plutonium-244 decay product.
Supernova and thermonuclear weapons both produce iodine-129 preferentially over plutonium-244. Mars didn’t experience a supernova, hence I propose that the xenon-129 excess, along with other evidence, is explained by a thermonuclear holocaust.
Advertisement
