- [Narrator] About the size of our moon, Io orbit's closer to Jupiter than any other moon of its size.

Since 2016, the space probe Juno has been our eyes on Jupiter and its moons.

With an elongated orbit, it has made regular flybys past Io, witnessing violent eruptions, which shoot out columns of gas and dust that reach far out into space and send rivers of lava pouring across the landscape, creating a surface dotted with lakes of lava.

Io is a volcanic powerhouse, defying all expectations.

- Considering how small Io is, the heat sources like we have on earth, the heat of formation and the radioactive decay, those should be essentially completely gone on Io by now.

- This little, tiny, small world of Io, you'd expect it to be geologically inactive.

Instead, it's the most volcanically active body in our solar system.

That's a surprise.

- [Narrator] Eruptions continue day in, day out across the entire surface, a world like no other in our solar system.

But similarities can be found by taking a closer look beneath the surface inside volcanoes here on Earth.

(text beeps) Astrophysicist Jen Gupta is entering a chamber created by a volcanic eruption over 4,000 years ago.

- The incredible thing about this place is that as the magma drained away, it left behind these colors that we can see here on the walls from elements and minerals that were dragged up from the interior of the earth during that volcanic eruption.

The one that immediately grabs my attention is the yellow.

This is from sulfates and sulfur, and these are the exact same colors that we see covering the entire surface of Io.

- [Narrator] Images of Io are dominated by its yellow surface, created by the same sulfates and sulfur that line the chamber walls here in Iceland.

- The scale of this place is just astonishing, and to think that there are chambers like this under the surface of Io, filled with molten magma ready to erupt out.

It's easy to think that Earth, our home planet, is completely unique.

But the more we discover about the solar system, the more we see these remarkable similarities like having volcanoes on Io.