Europa could have the essential ingredients needed for life:
Water is at the top of the list of ingredients that make life possible. It dissolves nutrients for organisms to eat, transports important chemicals within living cells, and allows those cells to get rid of waste. Data indicates Europa may have plenty of water – a salty ocean beneath its crust that contains more water than Earth's ocean. Scientists also think there's a rocky seafloor at the bottom of the ocean. The interaction between the ocean and the rocks could possibly supply chemical nutrients for living organisms.
The best evidence that there's an ocean on Europa was gathered by NASA's Galileo spacecraft, which orbited Jupiter from 1995 to 2003. The spacecraft made 12 close flybys of Europa and one of its instruments, a magnetometer, detected that a magnetic field was being created within Europa as Jupiter's powerful magnetic field swept past the moon. Scientists think the most likely thing that could create this magnetic signature is a global ocean of salty water.
Europa's surface also shows signs it could have an ocean beneath it. Images from Galileo and other spacecraft show that the surface doesn't have many craters from meteorite impacts like other moons in the solar system. Scientists think geologic activity, like warmer ice rising from below, could be erasing the craters over time.
Europa's bright, icy surface is a landscape unlike anything seen on Earth. To start with, in an overall sense, it's quite smooth, with few towering mountains or deep basins. Myriad ridges and grooves crisscross the surface, breaking up the landscape. Many of these features coincide with long, curving streaks that are dark and reddish in color – some stretching across the surface in great arcs over 600 miles (1000 kilometers) long. Elsewhere, domes, pits and chaotic jumbles of icy blocks hint that warm ice may be rising from deep below.
Models suggest that Europa's icy shell is relatively thin. The icy moon gets stretched and released by the tug of Jupiter's gravity, in an endless cycle, as Europa orbits the giant planet. This squeezing in and out is a process called tidal flexing, which may be creating heat inside Europa; the warmed ice from this heat may be pushing the surface upward to create the ridges.
The tidal flexing also may be creating enough heat inside Europa to maintain a liquid ocean beneath the moon's icy surface. Most of the heat would be focused at the boundary between the ocean and the icy crust.
For Europa to be potentially habitable, it would need to have the essential chemical ingredients for the chemistry of life. These include carbon, hydrogen, nitrogen, oxygen, phosphorus and sulfur, which are common elements, and scientists think it's likely they were present on Europa as it formed. Later on, asteroids and comets impacted the moon and would have deposited even more organic, or carbon containing, materials.
The chemical elements for life might be found within Europa's icy shell, as well as its ocean. Tidal heating could be powering a system that cycles water and nutrients between the moon's rocky interior, ice shell and ocean, creating a watery environment rich with chemistry conducive to life.
This is why studying Europa's chemistry – on the surface and within the suspected ocean – is important for understanding its habitability, because living things extract energy from their environments by chemical reactions.
All lifeforms need energy to survive. Where would life on an icy world far from the Sun get energy? The type of life that might inhabit Europa likely would not be powered by photosynthesis – but by chemical reactions.
Europa's surface is blasted by radiation from Jupiter. That's a bad thing for life on the surface – it couldn't survive. But the radiation may create fuel for life in an ocean below the surface.
The radiation splits apart water molecules (H2O, made of oxygen and hydrogen) in Europa's extremely tenuous atmosphere. The hydrogen floats away and the oxygen stays behind. Oxygen is a very reactive element, and potentially could be used in chemical reactions that release energy, which lifeforms could exploit. If the oxygen somehow make its way to the ocean, it could possibly provide chemical energy for microbial life.
If Europa does have a salty ocean, chemical reactions between the water and the rocks on the ocean floor could create hydrogen-rich materials. And if there are areas where the ocean interacts with hot rock, then, like hydrothermal vents in Earth's oceans, that water could be pouring out chemical nutrients to power life. In short, Europa may have a variety of processes that work together to make the chemical energy available for powering life processes of simple organisms like bacteria.