'Lineae' on slopes at Horowitz Crater are among the crucial pieces of evidence used to infer that water flows on Mars, but are quite insufficient for conspiracy theorists. NASA/JPL-Caltech/Univ. of Arizona

Even in a year rich with exciting astronomical news, NASA’s announcement on Monday of liquid water on the surface of Mars has stood out.

However, some people just can’t accept that the Solar System is a more exciting place than we knew. Instead, they have decided that it is all a conspiracy. A common feature of conspiracy enthusiasts is belief in directly contradictory claims; anything is possible as long as it’s not the official version. It's not surprising, then, that even those united by the idea that we couldn’t possibly have discovered something on Mars can’t agree on why we are being lied to, and what the actual truth may be.

Here are five Mars conspiracy claims in circulation.

1. It’s Advertising For The Martian

No doubt Ridley Scott and Matt Damon are pretty happy that Mars is at the forefront of people’s minds just as their film launches. But for the conspiracy-minded, coincidences don’t really exist. Instead, enthusiasts assure us the filmmakers paid off NASA to make the announcement. Like a lot of conspiracy theories, this one has a vaguely plausible version as well as one that is ridiculous. The mild version is that the discovery is real, but the timing was adjusted for commercial purposes.

Timing aside, there doesn’t seem to be any evidence for this, and it would require some tricky coordination with Nature Geosciences, who published the paper detailing the research. That being said, it’s probably not out of the question.

The really nutty version (for those not joking) is that there is no flowing water. In other words, a bunch of leading scientists – some of whom have been investigating this possibility for years – are willing to trash their reputations by making a huge announcement that is likely to be disproved. Not everyone is willing to lay down their life for their good name, but researchers usually place a high value on their own. The number of authors, and reviewers, whose credibility would be destroyed if this conspiracy theory were true is far too high for it to be likely that they are all in on the act.

2. It’s All About NASA’s Budget

A common objection every time NASA finds something exciting is that they’ve faked it to get Congress to bump up their funding. This one hasn't come out this time so much, but drill far enough into the comments on postings about the story and you can find people who think their tax dollars are being scammed. It's probably quieter this time because the more experienced conspiracy theorists are too busy saying "we knew all along".

While certainly government-funded agencies as large as NASA will always be concerned with maintaining and expanding their allocation, boom-bust funding is the enemy of good research. Moreover, nothing will hurt NASA’s future requests more than making a splashy (sorry, not sorry) announcement that gets disproved. Like everyone else, NASA scientists can be wrong, but if the agency gets caught manufacturing stories out of the thin Martian air, its long-term survival will be under threat. So unless you believe that everyone studying Mars, now or in the future, is in on the game, you should ask yourself why NASA would sacrifice its future for a one-year funding boost.

3. They’re Recruiting

“Why so late on this 'discovery' or is it simply an information release when NASA is now closer to actually getting astronauts to commit to a possible suicide mission to Mars?” asked one commenter on our report of this story.

Despite having a lot less credibility than the world’s foremost space agency, Mars One has been flooded with people eager to sign up for a shot at glory on the Red Planet. Even reports that this particular (private) project is a scam haven’t killed the enthusiasm. If NASA starts looking to send people to Mars, they won’t need to sweeten the deal with reports of hyper-salty water.

4. It’s To Cover The Existence of Martians

Yep, there are people who believe that Mars was once inhabited by intelligent life and that space researchers want to cover up this amazing fact. And scientists have chosen to do this by focusing the world’s attention on the Red Planet itself. We can’t even.

5. It’s A Left-Wing Plot

Science can’t always be divorced from politics, as many teachers have learned when they've tried to explain evolution to their class, but usually astronomy gets off lightly (budgetary questions aside). Nevertheless, the prominent right-wing radio host Rush Limbaugh thinks NASA’s announcement is part of Obama’s plan “to advance the leftist agenda.”

This one is so crazy that even Limbaugh, who let’s face it could make conspiracy theorizing an Olympic sport, can’t explain how it works. Instead, Limbaugh said, “I don't know what [the truth] is, I would assume it would be something to do with global warming.”

This allowed Limbaugh to segue into one of his favorite topics: how scientists are lying about global warming. “Look at the temperature data that has been reported by NASA,” Limbaugh said. “[It's just] been made up. It’s fraudulent for however many years. There isn’t any warming. There hasn’t been for 18.5 years – and yet, they’re lying about it. They’re just making up the amount of ice in the North and South Poles. They’re making up the temperatures. They’re lying and making up false charts and so forth.”

Conclusion

Limbaugh’s jump to an area of science with big policy implications shows why these theories matter. It may be fun to laugh at the people who believe Earth was terraformed by Martians, but it is unlikely their views will have a direct impact on anything. However, attacks that undermine the credibility of research agencies, and the scientific method itself, make people less likely to consider evidence seriously when important consequences are at stake.

On the other hand, learning to sift through evidence in one arena can be good practice for others, which makes the teaching of critical thinking skills important, and explains why some people want to ban teaching them in shools.