The Search for Life in the Subsurface Ocean of Europa

NASA Goddard Space Flight Center

The airless, frigidly cold Jovian moon might not sound like the most promising environment for finding extraterrestrial life, but it’s what’s beneath the surface that’s most interesting. The subsurface ocean of Europa might just be a haven for exotic life.

Scientists are almost unanimously agreed that there’s an ocean beneath Europa’s icy crust. This vast water ocean is kept liquid beneath up to 19 miles (30 km) of ice as hard as granite by tidal heating from Jupiter, as evidenced by plumes of water vapour erupting from breaches in the surface.

Earth-like Life 370 Million Miles Away

National Undersea Research Program

Hydrothermal vents are home to rich ecosystems despite living completely independently from the Sun’s light and heat.

The subsurface environment of Europa presents the perfect home for life like those found in fully independent ecosystems around Earth’s hydrothermal vents. There’s plenty of water, and the ocean could be as deep as 100 miles (160 km). Many scientists also believe that Europa’s ocean is heavily oxygenated. However, the trace amount of the gas found in the moon’s tenuous atmosphere are not believed to be biologically generated, unlike on Earth.

Although no hint of sunlight ever reaches these murky depths, that doesn’t preclude life from existing in this vast global ocean. In fact, Earth’s hydrothermal vent ecosystems are alive and well, despite being so deep that the Sun has no influence. Everything from giant tube worms to clams and limpets live and thrive at these vast depths, even though their food chain doesn’t rely on photosynthetic organisms at any stage. Instead, they ultimately draw their energy from the deep-sea volcanic fissures.

There seems to be no reason why such conditions couldn’t be much the same on Europa. As such, this fascinating moon is often touted as being one of the most likely places in the solar system to find extraterrestrial life. Thanks to the presence of hydrogen- and oxygen-producing activities, such as melting ice on the underside of the crust, the gloomy depths of Europa’s oceans may be very much like our own.

Exploring a Hostile Environment

NASA/JPL-Caltech

NASA’s latest Europa Lander Concept is intended to search for biosignatures and signs of habitability that have made their way to the surface of the moon.

As is often said, we now know more about the surface of Mars than the bottom of our own oceans. After all, the deepest reaches of the ocean are notoriously difficult to explore, owing largely due to the extreme pressures. Landing something some 370 million miles (600 million km) away and exploring an ocean that lies far below a rock-hard icy surface is easily a thousand-fold more complicated. However, that doesn’t seem to be putting NASA off from trying.

On February 8, 2017, NASA revealed that it received the first pre-phase planning proposal for a mission to Europa. With the proposed launch slated for 2031, we might have to wait a while, but the mission has some very important goals. The proposed lander will be built with the ability to hunt for biosignatures and habitability characteristics. It is also intended to help pave the way for future missions that may even go so far as to drill beneath the crust and explore the ocean directly.

Although we’re still a long way off in terms of budgetary constraints and feasible technology, the ultimate proposal for a mission to Europa concerns sending a submarine to explore the ocean. Before this becomes a possibility, however, the world’s space agency must set its eyes on more attainable goals.

The proposed 2031 lander mission will be looking for biological material. If there is life in the subsurface ocean, it should also leave its mark on the surface and in the atmosphere by way of water vapour plumes erupting from beneath.

Extreme Fish in an Alien Ocean

NASA/JPL-Caltech

Europa’s surface might be bitterly cold and completely devoid of life, but the subsurface ocean that lurks beneath may tell quite a different story.

There’s a reasonable chance that any life found on Europa need not be restricted to that of microbes. In fact, evidence suggests that chemical makeup of the salty water should be like that of Earth’s oceans. What’s most interesting is the age of its surface which, owing to the rarity of impact craters, is estimated to be no more than 50 million years old. In other words, the moon has been resurfaced many times over the four billion years it’s been around.

Simulations show that the resurfacing of Europa creates oxygen as ice melts from the lower levels of the crust due to tidal heating and flexing. This process constantly renews and regenerates the surface crust, which is forever being pushed, pulled and warped by the immense gravitational forces of Jupiter. This is precisely why the surface of Europa is partly covered in cracks and ridges which are, appropriately, named ‘Chaos Terrain’.

While it’s certainly exciting to imagine giant squid-like creatures swimming around in the Europan ocean, as portrayed in the film Europa Report, this might be overly optimistic. On one hand, the recent resurfacing of the moon would have such a profound effect on any life beneath that it’s hard to imagine anything other than microbial life surviving such changes. Nonetheless, if Europa is also home to hydrothermal vents pouring out life-giving heat and chemicals, the possibilities look very promising indeed.

Starting the Search Closer to Home

| Earthly Universe

In 2015, Russian scientists working at Vostok Station, managed to drill a clean hole through nearly 2.5 miles (4 km) of ice to reach the lake beneath.

Much closer to home, albeit in an environment that’s unbearably hostile to we humans, scientists are discovering just how resilient life on our own planet is. Even some of the world’s most hostile environments are home to rich ecosystems, despite them being no less alien to us than the subsurface oceans of Europa.

Lake Vostok is located far beneath the ice in the heart of Antarctica. The ice here is hundreds of thousands of years old, and it extends almost 2.5 miles (4 km) below the surface. Beneath is an enormous lake, the water of which hasn’t seen the light of day for millions of years. Right here on Earth, it’s the perfect analogue to the conditions that we expect to find on Europa and on Saturn’s moon Enceladus.

Researchers working at Vostok Station reported in 2015 that they had sampled DNA of around 3,500 species that have lived and may still be living in the depths of lake Vostok. Many possible microorganisms have been found, most of which have yet to be classified and assigned scientific names.

One thing’s for sure, however, and that’s that any life found lurking in the depths of Lake Vostok bodes well for the hunt for life on faraway Europa.

What do you think about our chances of finding life on Europa or elsewhere in the Solar System and Beyond? Let me know in the comments below!