Say you’ve made a great astronomical discovery. What if you’re wrong?

Again, though, independent scientists took a look couldn’t replicate the original findings. They concluded that the claim of arsenic-based life was wrong. But John Tainer, a Lawrence Berkeley National Laboratory researcher who is still working on the bacterium, isn’t deterred. “There are many reasons not to find things,” he told the Washington Post. “I don’t find my keys some mornings. That doesn’t mean they don’t exist. The absence of a finding is not definitive.”

The list goes on, and as the search for a truly Earth-like planet heats up, thanks largely to the wildly successful Kepler Space Mission, the race to be first to find one has led to at least one more questionable discovery—a planet known as Gliese 581g, which co-discoverer Steve Vogt described as “a place where life has a lot of chances of having a foothold.”

Except that most experts in the field think Gliese 581g doesn’t exist. “I suspect that the analysis was not done as carefully as it could have been,” Eric Ford, an astronomer at the University of Florida told me for my chapter on the controversy in Mirror Earth. “I was skeptical as soon as I read it.” In short, Vogt and his collaborator Paul Butler may have screwed up.

But like the other scientists whose discoveries have been widely rejected by their colleagues, Butler and Vogt continue to insist that their planet is really there. And it’s not enhancing their otherwise excellent reputations. When the first true twin of Earth is finally discovered—and it could happen literally any day now—you can be sure that whichever research team finds it has put enormous effort into making sure they aren’t fooling themselves.