In KNOWN, I explain that life must exist in Europa and Enceladus. Statistics offers the answers.
In all 122 seas on Earth, microscopic life lives. No large lifeless body of saltwater exists. Therefore, it’s valid to ask whether Europa’s ocean – which is over twice as big as all Earth’s oceans – harbors microbials. And since I have no example in nature of a large saltwater body that is lifeless, I must conclude that Europa holds life.
The key to applying statistics is to equate initial conditions between Earth’s seas and Europa’s sea. I find a starting point in the common origin of Earth, Jupiter, and its moon Europa. All came from the same solar nebula. I might look to the original Big Bang as a common source that created all the elements. Further, comets have visited Earth and all the planets and their moons. So Earth and Europa are not entirely separate worlds, despite that traditional view.
What was the “New World” centuries ago is now viewed as part of the same world as the old. The same logic applies to Europa. Despite the distance that separates it from Earth, Europa is part of the same planetary system as Earth. Earth and Europa aren’t truly separate worlds.
Microbes see the same thing in Earth’s saltwater and Europa’s saltwater. Both groups of microbes thrive in a mixture of hydrogen, oxygen, and sodium. Both bodies of saltwater are irradiated.
After equating initial conditions, I apply statistics to prove that life must live in Europa. Europa is essentially the 123rd body of saltwater to be explored. No data is available for that 123rd saltwater body, but the other 122 saltwater bodies harbor microbials. Since the initial conditions are the same, the probability of life in Europa is at least 122 out of 123, or over 99%.
The same argument applies to Enceladus, which spews saltwater into space. Those plumes even bear organic chemicals, as do some comets!
Statisticians commonly apply such high probabilities to accept a theory. When the probability of a hypothesis is over 95% – or when a theory holds true 95% of the time – the statistician accepts that hypothesis and rejects any alternative hypothesis. Meteorologists apply this logic constantly.
Just as meteorologists “know” that a given dry desert will offer a dry day in a certain period, so too astrobiologists know that life lives in Europa and Enceladus.
So what questions should astrobiology consider next? Do larger life forms exist? Does intelligent life exist? What new life forms live? The new questions will drive astrobiology for decades.