As far as we know, we have not yet found extraterrestrial intelligence. The Drake equation attempts to explain the number of civilizations in our galaxy as a product of seven factors:

\[N = R_* \cdot f_p \cdot n_e \cdot f_l \cdot f_i \cdot f_c \cdot L\]


\[\begin{align*} R_∗ &= \textrm{the average rate of star formation in our galaxy} \\ f_p &= \textrm{the fraction of those stars that have planets} \\ n_e &= \textrm{the average number of planets that can potentially support life per star that has planets} \\ f_l &= \textrm{the fraction of planets that could support life that actually develop life at some point} \\ f_i &= \textrm{the fraction of planets with life that actually go on to develop intelligent life (civilizations)} \\ f_c &= \textrm{the fraction of civilizations that develop a technology that releases detectable signs of their existence into space} \\ L &= \textrm{the length of time for which such civilizations release detectable signals into space} \\ \end{align*}\]

Clearly something in the Drake equation makes it extremely unlikely for intelligent life to exist. The Great Filter is a name for whatever that is. The great filter might be in our past (e.g. if \(f_l\), the fraction of planets that will develop life, is extremely small) or it might be in our future (e.g. if \(L\), the length of time that space-capable intelligence civilizations exist, is extremely small). We hope that it’s in our past since otherwise we’re bound to not exist for much longer.

Now, let’s say we find non-intelligent life on one of Jupiter’s moons. The fact that another planet (in our solar system, no less) has developed life means we’d have to greatly update our prior on how unlikely \(f_l\) (the fraction of planets that will develop life) is. And if non-intelligent life is relatively common, but intelligent life is rare, that means the great filter is likely not behind us!

So, in this sense, finding life on other planets would be extremely terrible news for our future.

For a more comprehensive treatment, see WHERE ARE THEY?.