A nuclear explosion on Mars? Not likely…
An article by SF writer Charles Stross has been doing the rounds over the past week, describing an LPSC abstract which mentions “evidence” for a possible ancient nuclear explosion on Mars, caused by a “natural nuclear reactor” going critical. A lot of folks seem to be getting a bit excited by this because (not unreasonably) they think that since it’s published it must be scientifically valid, and I feel obliged to put on my party pooper hat and point out that it probably isn’t.
So first things first – here’s the LPSC abstract.
Now, you may be surprised to know that there IS actually such a thing as a “natural nuclear reactor”. We have evidence that at least one existed on Earth – at Oklo in Ghana – and you can read all about it on its wikipedia page. Essentially, you can get circumstances occurring in nature that are similar to those that occur in a nuclear fission reactor, if you have the right combination of geology, radioactive ore bodies and groundwater acting as a moderator. (you’ll note that the Mars “reactor” got a mention on the wikipedia page – that’s likely to be disappearing soon, given the scrutiny the abstract is now receiving).
So, why should we be skeptical of this LPSC abstract?
Peer review
Peer-review is a pretty important part of scientific methodology – it’s the process by which ideas are discussed and scrutinised and criticised and accepted (or rejected) by the scientific community. For a paper to be accepted for publication it must pass the peer-review process, which means that experts in the field have looked at the science, examined the evidence, and possibly duplicated any described experiments themselves and verified that the conclusions reached are valid. If they don’t then the paper is rejected, and the authors must either do more work to demonstrate their hypothesis or just start again and try another approach (or move on to something else). However, the article being discussed here is not a paper, it’s a conference abstract.
Conference Abstracts are not the same as papers. Conference abstracts are normally short summaries of work in progress – especially for teams working on ongoing missions – or interesting hypotheses that could be considered, and they may or may not be developed into papers later on (LPSC, DPS, and AGU are three of the big planetary conferences where abstracts are presented). Some are presented at the conference as posters or talks where they can be discussed further. Some of them get shot down, some pass scrutiny – that’s how science works. I’ve submitted and presented a few LPSC abstracts myself while I was at university – some worked out, some didn’t. The important thing though is that they are not peer-reviewed at all.
At this point I would like to strenuously and enthusiastially point out that the vast majority of abstracts submitted to LPSC are perfectly good science written by scientists and students of science. However, because (as far as I’m aware) the abstracts are not checked or vetted after they’re submitted, a handful of abstracts about… well, I’ll be charitable and call them “less likely scenarios” do slip through. For example, I remember reading one abstract a few years back suggesting that the sun had accreted around a neutron star – which makes no sense in terms of stellar formation/evolution at all. It probably got a few chuckles from those who noticed it, but otherwise it passed by unnoticed at the conference itself because its authors didn’t show up to elaborate on it (granted, a lot of authors aren’t able to turn up to LPSC for many reasons – but if you have a controversial idea then it helps if you show up to defend it!).
So – the important thing to be aware of here is that this is an LPSC abstract that has not been peer-reviewed, which means that its conclusions should be viewed with quite a bit of skepticism.
What about the science though?
There are questions to be raised about the author’s credibility – it doesn’t help that he previously authored an article suggesting that the so-called “Face on Mars” was created by an ancient martian civilisation (even if there ever was any doubt about its origins – not that I think there was – we now have plenty of evidence to show that it’s a completely natural feature). But be that as it may, the proper way to proceed is to analyse the science. Unfortunately, it seems to me that the science in the paper is not very good. Here are a few issues I found:
a) he says that the “reactor” was “tamped” by the overlying rock but doesn’t provide any calculations to support this (and for all I know he forgot that Mars has lower gravity than Earth, so pressure is lower at a given depth). That’s a fairly critical part of the scenario that we just have to take his word for.
b) He also doesn’t provide a satisfactory explanation of how the radioactive ore body forms and how it’s concentrated on Mars in the first place (radioactive ores are not usually concentrated by asteroid impacts).
c) He doesn’t provide any evidence for this supposed explosion beyond “it looks like the radioactive stuff was concentrated around a depression” which could have been caused by a number of other means (e.g. it could have been an depression caused by an ancient asteroid impact). Occam’s Razor seems sorely lacking.
d) I didn’t see a source mentioned for the maps of K and Th distribution presented in the abstract.
e) We know of precisely one natural nuclear reactor on Earth, which implies that they’re somewhat unlikely to form… and it didn’t blow up. And yet there was supposedly one on Mars that did? Seems like a lot of unlikely coincidences would have to line up to make that happen on the next planet over from us.
f) And he spends a lot of time telling us his interpretation of the data, and not a lot of time just objectively describing the data and saying what other options could explain it.
g) if this happened so long ago, why would there be evidence left on the surface after a billion years of deposition and erosion (and redeposition) by the winds that scour the surface of Mars? Surely that would have redistributed the material (if not hidden it)?
And this is before I even get to the nuclear physics side of it… I’ll leave that for others more knowledgeable about the subject. Either way, while some discussion and dissection of the evidence is happening now on various internet fora (now that it’s got some attention), so far the verdict is that the evidence to support the hypothesis is lacking.
So in the end I’d say that the “evidence for a nuclear reactor on Mars” – particularly one that exploded and blasted radioactive material across the planet – seems to be rather unconvincing! It’s an interesting idea to examine and dissect (that’s pretty much why it’s there, after all), but this does show that we need to always critically assess what we see on the internet so that we don’t mistake unreviewed conference abstracts for peer-reviewed science!
[b]Addendum[/b]: And funnily enough, this LPSC abstract even gets a mention in this rather excellent video (around the 2:47 mark) explaining how the popular media often doesn’t really understand the science it reports.
