# What is the probability that there is life on other planets?

From a mathematical point of view, what is the probability that

1) There is organic life on other planets

2) There are advanced species like us or even greater than us on other planets?

Is there a formula or equation or a way we can calculate this probability?

• Somewhere between 0 and 1. Nov 6, 2017 at 23:01
• In my personal opinion, there is even an extra distinction to take care of: there might be life, elsewhere in our galaxy, based on the same structure as ours (proteins, forming DNA), based on the "panspermal" theory, and their might be life which looks entirely different. Jan 23 at 13:31

The probabilites are unknown at the moment (March 2014), since there is only one known planet (Earth) harboring life. This doesn't allow any meaningful probability estimates for the occurence of life, based on empirical data.

The overall formation of life is too complex to allow simulations based on current technology. Although some intermediate steps can be simulated or performed by experiment, e.g. by the Miller-Urey experiment.

The Drake equation is a simplified attempt to decompose the probability into factors. Some of the factors aren't known yet. But there has been much progress in estimating the frequency of exoplanets, and the probability of planets to be habitable. From this news release one could estimate (order of magnitude), that there is one habitable planet around a Sun-like star per about 1,700 (about 12³) cubic light years in our region of the Milky Way ("... the nearest sun-like star with an Earth-size planet in its habitable zone is probably only 12 light years away...").

We don't know the probability for habitable planets to develop life, nor to be colonized. Probabilities of complex life forms are even more difficult to estimate (yet). More discussion about habitability of exoplanets on Wikipedia.

• Thanks Gerald I have greatly enjoyed reading on the Milley-Ulrey experiment and the Drake equation. While the former experiment proves that a habitable planet will mostly likely develop life the odds of that life becoming intelligent enough to colonize seem quite low as is evidenced by our planet. But then there are uncountable galaxies in the observable universe so a low non zero probability of planets with intelligent life could still translate to many intelligent life forms out there. Mar 19, 2014 at 16:11
• @nemesis22 That's plausible; may be there are billions of intelligent life forms in the observable universe, but it's hard to prove. Mar 19, 2014 at 18:07
• One observation, yes, and that one is statistically invalid since we are the observer observing ourselves. Our existance is exactly as likely in a universe where we are alone as in a universe where we have company: 100%. Mar 20, 2014 at 9:34
• Drakes equation should take relativity into account... It'll significantly reduce the chances for life existing elsewhere; as seen by us. Sep 1, 2014 at 18:52

I shall answer this old question with new information! I'd like to keep this question relevant for future readers.

On January 17th 2022, NASA released the following statement:

"Scientists today announced that several of the samples are rich in a type of carbon that on Earth is associated with biological processes."

So yeah, chances are something was alive there at one point or another. Gale crater (the massive hole-in-the-ground that Curiosity calls home) is in a favorable location for life.

As James K has brought up, the fact that Curiosity found carbon doesn't change anything. If there is or ever was anything in that soil would require close observation with a microscope to prove it, which the MSL (Curiosity) rover is not equipped with. The NASA source states that since there is carbon, carbon that is usually associated with biologic processes, the likelihood of life on Mars may be higher than what is stated in the other answer, there just hasn't been enough science power of this particular spacecraft to prove such a thing, and therefore this may be partially based on theory. However, life on Mars period is just a theory. Because this question is more about just on other planets in general, I should address those, but Mars is the most famous example of this. If I had to guess, I'd say there's about a 50% chance that there was something in Gale crater at some point, but I think the chances of life on Europa (A moon of Jupiter) are around 60-70%.

As for my favorite mars rover of all time, Perseverance, no word yet on any carbon, bacteria, or anything living whatsoever. But I believe that Perseverance will find something of this nature sometime during its mission since it is equipped with a microscope. And, let's face it, Perseverance is just so much better than Curiosity (No offence, my robot friend Curiosity, but you're just no longer the new shiny thing).

• "While the finding is intriguing, it doesn’t necessarily point to ancient life on Mars" - (your source) So your conclusion "something was alive there at one point of another" is not found in your source. Instead you should say "While this is consistent with ancient life, there are several other, plausible, non-biological explanations, so the probability that life was once on Mars can still only be estimated as 'between 0 and 1'" Jan 20 at 22:49