- [Narrator] A key ingredient from the ocean below surges up through the cracks, giving Europa's markings their distinctive red.

- So the red marks that we see on Europa's surface, these cracks and lines, are salts that have come up from below the surface.

- [Narrator] Suggesting a tantalizing possibility.

This crisscrossing system of salty canyons means we might find life in the ocean underneath Europa's icy shell.

- Life as we know it needs three basic things: water, a source of energy and also essential elements.

- [Narrator] Europa has an ocean and a source of energy from tidal movements, but it's missing the final key ingredient, some essential elements.

However, with a little help from its neighboring moon Io, these elements can be found on Europa.

- Io is an extremely volcanically active place, and these volcanoes emit sulfur and other sulfur products.

And these make it all the way onto Europa, and sulfur is one of those essential elements that life on Earth uses.

- All of the sulfur that's coming from Io and landing on Europa's surface is interacting with the salts and water that's coming up from underneath Europa's icy crust.

- [Narrator] Chemical reactions between the sulfur from Io and the salts on Europa create essential molecules needed for life.

- And this allows for this perfect breeding ground for potential life to form and evolve.

- [Narrator] Europa is such a strong candidate for life that NASA is already preparing to explore the moon.

The goal is to study Europa's surface in more detail so that a future mission can one day land and explore beneath its icy crust; and scientists like Sam are already testing ideas for studying Europa's watery world.

- What we're doing is we're deploying a robotic probe into the ice and under it to explore what this lake environment is like.

We might have the opportunity in my own lifetime to answer a question that's intrinsic to all of us: are we alone in our universe?

Are we alone in our solar system?

And one of the most exciting aspects of exploring Europa is the potential of someday knowing whether or not there's life in our own solar system.

(tense music)