According to plasma physicist John Brandenburgassociated with a NASA affiliate, multiple nuclear explosions occurred on Mars around 180 million years ago. To what extent is his evidence correct, and are these alleged nuclear explosions of natural or artificial origin?
Mars ravaged by nuclear war?
Mars is a barren wasteland right now. The scarce water on Mars is like ice on the polar caps and in thick layers of permafrost in the bottom. Billions of years ago it was different. Mars was covered by shallow oceans and had a climate similar to the Earth's polar regions today. Rocks have been found in several places on Mars that look a lot like fossil stromatolites, a rock formed by bacteria. It is therefore not implausible that, billions of years ago, primitive, unicellular life existed on Mars.
John Brandenburg continues. He thinks that there were technically advanced creatures on Mars, wiped out in nuclear war . Extraordinary claims extraordinary evidence, as the Americans say, so we'll look at the facts at hand, and whether the nuclear war in the distant past is indeed the most obvious explanation.
The History of Mars, According to Brandenburg
Contrary to the mainstream view, Brandenburg believes that Mars was not around 3.5 billion years ago, the so-called end Noachian era, but only about 0.2 billion years ago turned into the arid, anoxic wasteland of today. This would mean that biological evolution on Mars had nearly as much time at its disposal as that on Earth, and that it would in principle have been conceivable that a technically advanced species had developed. Brandenburg thinks this is true and that the “artificial” formations described by UFO adepts are not natural rock formations but the remains of an extinct indigenous civilization.
Some heavy nuclear explosions occurred on Mars around 180 to 1500 million years ago. Brandenburg concludes this on the basis of the very large amount of xenon-129 and argon-40 in the Martian atmosphere and the high concentrations of thorium and uranium, ten times those on Earth, on the surface of Mars.  In  he attributed this to a natural nuclear reactor, like the one on Earth 2 billion years ago, where now the Gabonese town Oklo was found. It would have run wild and destroyed the planet in a terrible explosion. Now he rejects his original hypothesis, because no trace of an explosion crater has been found on Mars. A natural nuclear reactor also releases much less xenon-129 than has been found on Mars. He thinks that a civilization outside of Mars caused these explosions because the high concentrations of radioactive isotopes are close to sites of supposed “alien ruins” . These are also the places where minerals resembling trinite (radioactive glass, formed by nuclear explosions) have been discovered . The implications of this are pretty dire. If he's right, our part of the Milky Way is dominated by an entity that isn't very fond of intelligence. Does our species face such a fate, and does this explain Fermi's paradox?
Is the hypothesis of an alien nuclear war correct?
Mainstream scientists reject Brandenburg's theories . However, given his successful previous scientific career, the man cannot simply be dismissed as a crackpot and clearly knows what he is talking about, see also his comments under .
To blow up Mars according to Brandenburg's theory, quite a bit of radioactive material is needed. He mentioned about 0.1 cubic kilometer as a value and an amount of energy released of 1025 joule. That is a sphere of slightly more than 200 meters in diameter, resp. the amount energy which the complete sun radiates in a tenth of a second. To give an impression: that bomb would require 100 times as much uranium and thorium as can be found in recoverable reserves on Earth.
It doesn't seem very useful to deploy one or two giant hydrogen bombs. Nanotechnology or a genetically engineered virus, or a diverted comet for that matter, is equally effective against a fraction of the resources needed. We can safely assume that an alien race smart enough to cover distances of light years will choose smarter solutions. A slightly more likely scenario would be that the hypothetical Martians fought a nuclear war among themselves - the Earth's nuclear arsenal is more than enough to destroy the planet. An all-out nuclear war on Mars would have left little of the planet. This scenario, too, would require Mars to remain warm and humid for much longer than current theories indicate. Nor does this explain the hotspots.
Based on physical principles, Brandenburg's theory is quite rattling and does not seem plausible. However, the measurements on which he is relying are unquestionable and indicate that our theories about the history of Mars are incomplete and flawed on important points. He also certainly has a point regarding Fermi's paradox. There may be a deadly danger between the stars, killing germinating civilizations at an early stage. We better prepare for that as soon as possible and try to safeguard the survival of our species and our world.
Given the importance of answering these and other questions, a manned mission to Mars is desperately needed.
1. John Callaghan, Were Martians wiped out by a nuclear bomb? Physicist to present new evidence for bizarre theory at Nasa conference, Daily Mail (UK), 2015
2. JE Brandenburg, Evidence for a large, natural paleonuclear reactor on Mars, 2011.
3. JE Brandenburg, EVIDENCE FOR LARGE, ANOMALOUS NUCLEAR EXPLOSIONS ON MARS IN THE PAST, 46th Lunar and Planetary Science Conference, 2015
4. JE Brandenburg, Evidence of a Massive Thermonuclear Explosion on Mars in the Past, The Cydonian Hypothesis, and Fermi's Paradox, Journal of Cosmology, 2014 (copy locally stored because original article is no longer retrievable)
5. The two faces of JE Brandenburg, Pharyngula Science Blog, 2014