With the Europa Clipper mission, NASA hopes to find signs of life

On October 10, NASA's Europa Clipper will hopefully begin a five-year journey to look for the components necessary for life in one of the most promising places in our solar system.

Europa, one of Jupiter's 95 moons, is about the size of our moon. It's completely covered in a layer of ice that planetary scientists estimate to be between 15 and 25 kilometres thick. And under that ice, those scientists believe there is a salty ocean containing twice as much water as all the oceans on Earth.

This unmanned mission to Jupiter's neighbourhood is expected to determine if that giant ocean could contain the building blocks of life.

In 1979, when Voyager One flew past Jupiter, I was among the press and scientists who got the first close-up look at the giant planet's four "Galilean" satellites: Io, Europa, Ganymede and Callisto. These are the same moons that Galileo saw through his early telescope in 1610, and that you can see today with a small telescope or a good pair of binoculars. 

It was like being a crew member on Magellan's ship sailing around the world when the lookout in the crow's nest hollers, "Land Ho!" — except the new land we were seeing was a truly alien world.

During the approach, we watched Jupiter appear as a roiling maelstrom of colourful clouds, swirling around with hurricane force, and a giant red spot larger than the entire Earth. That was generally anticipated. But the moons were largely unknown, having appeared as mere dots in telescopes since Galileo's time. As these strange worlds came into view, everyone was amazed at how each of them was dramatically different from the others in surprising ways.

This became the hallmark of the Voyager mission as it flew past all four of the giant gas planets, Jupiter, Saturn, Uranus and Neptune. But at each encounter, the moons were the stars of the show because they were all so distinct and unusual. We were all on a voyage of pure discovery.

The moon Io looked like something that had been left in the back of a refrigerator too long, with a blotchy yellowish-orange colour due to dozens of sulphur volcanoes erupting on its surface. Ganymede and Callisto were covered in craters like our moon, but with a lot of ice mixed in with the dirt.

Then there was Europa, the brightest of the four, with a completely smooth, cream-coloured surface with no craters or mountains, a surface so even that it resembled a white cue ball from billiards.  

The only explanation for such a uniform, bright surface was a thick layer of ice covering the entire moon from pole to pole. Closeup images revealed long dark lines criss-crossing the surface that turned out to be huge cracks where the ice had separated and new material rose up from below. That meant the ice was floating and moving around like sea ice in the Arctic. And since the cracks are found all over Europa, there must be a global ocean beneath the ice.

More detailed observations of Europa by the Galileo spacecraft that orbited Jupiter between 1995 and 2003 determined that the ocean is salty and immense. It's astounding to contemplate an icy moon with more water than our blue planet. 

But what scientists are really excited about is what this could mean for the search for life in our solar system. On Earth, wherever there is water, there is life, from high in the atmosphere to the depths of the ocean and even deep underground. Since life can thrive in extreme environments on this world, why not the dark depths of Europa's ocean?

It takes at least three conditions for life: water, energy and chemistry. Europa appears to have all three. There is obviously lots of water, and observations by the Hubble Space Telescope have found signs of water plumes, which may have erupted through cracks in the ice. The James Webb Space telescope found carbon dioxide on the surface, which is a good sign because all life on Earth is based on carbon. 

Europa Clipper is designed to examine those water plumes more closely and look for more organic chemicals, the building blocks of life. 

Powerful tidal forces from the influence of the other moons and enormous gravity of Jupiter squeeze the moon like an exercise ball in the hand that could generate heat in the moon's core and provide energy from within.

The example from Earth that might be relevant is the life found in the darkest depths of our oceans. Hydrothermal vents, where hot water pours out of cracks in the ocean floor, support a wide variety of life from the microscopic to giant clams, crabs, and unusual tube worms as long as a human is tall. 

These organisms thrive in permanent darkness, relying on chemosynthesis rather than photosynthesis, allowing bacteria that thrive on minerals in the hot water to provide the base of the food chain for other organisms. Could there be similar hydrothermal vents and oases of life in the dark seas of Europa?

The Europa Clipper mission is a big step toward answering that question. The spacecraft will enter orbit around Jupiter and make several close flybys of Europa to determine how thick the ice cover is, the amount of water in the ocean, and also to look for gases that could be coming up through cracks in the ice. 

Those cracks may offer opportunities for a future mission equipped with a lander and probe to either drill or melt through the ice to reach the ocean below. However, such a mission will have to proceed with extreme caution to make sure that we do not contaminate Europa's water with Earthly organisms. The last thing we want to do is discover alien life then wipe it out with a pandemic.

Europa is just one of many ice worlds scattered throughout the solar system. Enceladus, a moon of Saturn, also has a cracked ice surface and geysers of water spewing out into space. Titan, another Saturnian moon, has liquid methane lakes on its surface and possibly a liquid ocean below. Even distant Pluto may have a liquid layer below ground.

The search for alien life is commonly thought to be focused on finding Earth-like planets orbiting other stars, but perhaps our alien neighbours are hiding inside ice worlds right here in our solar system. They won't look like us, but just finding them will tell us that we are not alone in the universe.