searching for life on Europa
Piggy-backing on my last blog post SETI thoughts, I've also learned more about our search for life on moons in the outer solar system.
Apparently over the last few decades, humans have gathered evidence to suggest that several of the moons orbiting Saturn and Jupiter have thick layers of ice above liquid water oceans.
Right now, NASA is studying Europa, one of Jupiter's innermost moons. The Europa Clipper mission launched in October 2024 and will enter Jupiter's orbit in April 2030 after traveling 1.8 billion miles. Whilst orbiting Jupiter, it'll conduct 49 flybys of Europa, taking pictures and capturing various data. The purpose of the mission is to determine whether Europa has the conditions suitable to support life. If it does, we'll have to send another spacecraft out there to look. I'm relatively young so it's very possible that within my lifetime, we could find extraterrestrial life on Europa! Damn!!
I read a book called Alien Oceans: The Search for Life in the Depths of Space by Kevin Peter Hand. He's a planetary scientist, astrobiologist, and the Director of the Ocean Worlds Lab at the Jet Propulsion Lab (JPL) at NASA. His interview on the Startalk podcast with Neil deGrasse Tyson is a fun overview.
how could liquid water exist in the outer solar system, you ask?
we once thought a planet or moon needed to exist within the traditional "habitable zone" of a solar system to hold liquid water. The traditional habitable zone theory was based on an object's proximity to its star: it couldn't be too hot (too close), too cold (too far), but just right.
But it turns out--dun dun dun--that liquid water can exist on objects that were once thought to be too far away from its star. How? Liquid water gets trapped under a thick layer of ice, insulating it from the brutally cold atmosphere.
Well actually, liquid water needs a little more than just a thick layer of ice to exist so far away from its star. It can exist on an icy moon as long as that moon has an elliptical (not cylindrical) orbit around a giant planet with a strong gravitational force (like Jupiter has on Europa). The push and pull that these celestial objects have on each other generates heat which supports the liquid water. That's how Europa can be in such a cold territory but still have enough heat for liquid water.
how do we know Europa has liquid water oceans underneath the ice?
We can't say with 100% certainty just yet. That's what the Europa Clipper mission is trying to prove. But we do have strong evidence to suggest that it's there, which helped justify the Europa mission in the first place.
Images from the Galileo and other spacecrafts have shown an icy layer with big fractures, suggesting tectonic activity. There's also something about spectroscopy--we can see rainbows on Earth because of the way the light interacts with water droplets which act as prisms. Apparently we can see the same thing happening on Europa.
Let's say the Europa Clipper confirms the presence of liquid water oceans. What are the chances that stuff is alive there, right now?
Somewhere between 0% and 100%. It turns out that life is a needy little bitch and requires a lot more than just water. It also requires specific elements from the periodic table--check out this 2004 article from Wackett, Doge, and Ellis with an awesome color-coded periodic table indicating which elements are necessary for life. And finally, life also requires the right amount of density/rocky materials. (Apparently a planet/moon can't be 100% liquid water without any interaction with rocky materials, or without any carbon, hydrogen, nitrogen, oxygen, phosphorus, or sulfur (CHNOPS).
The Europa mission seems promising to find evidence of life in our solar system, in our lifetimes (depending on your age). We have a specific object that we think is a top candidate and we can send a data-collecting spacecraft there in less than a decade. And while any life that exists on Europa is likely unintelligent life, it doesn't really matter--just knowing that life does exist outside of Earth would be a massive discovery. It would fundamentally shift how we think of ourselves in the universe.
And it might fundamentally shift how we understand biology. Life on Earth is formed from a DNA-based system (DNA, RNA, APT, and protein). If we find life on Europa that is formed on a completely different system, it'll rewrite our textbooks. It might help us make advances in medicine. We'd have a whole host new microbes in a new microbe kingdom, or even new animals in a new animal kingdom. No matter what, finding life on Europa would be mind-bogglingly cool, and if it exists, we're damn close to finding it.