The European Space Agency also approved the development for the Jupiter Icy Moons Explorer, ( JUICE), currently scheduled to reach Jupiter’s system in 2029.
It was believed that at the dawn of space age all life is ultimately dependent on the energy of the sun. It seemed impossible that any life could exist on the frozen ice balls of outer planets. The discovery of vibrant ecosystems in the depths of the Earth’s oceans, which rely on hydrothermal vents as both a source of energy and a molecular fuel changed everything. We now know that life can flourish in environments completely cut off from the sun.
Europa’s liquid interior ocean is believed to have the ability to support simple, microbial living beneath its icy surface. It has all three of the essential requirements for life: biochemically useful molecules; energy sources and liquid solvents (water), in which dissolved materials can react chemically with each other.
Europa’s energy is a result of its slightly elliptical inclination around Jupiter, and the gravitational interactions with two other satellites. The combination of these forces causes Europa to flex with each orbit and release heat. This prevents the water freezing.
Europa’s biochemically valuable molecules could come from comet impacts or deep within the rocky core of the moon.
Ice penetrating radar
Europa Clipper and JUICE both carry radar instruments that will probe beneath Europa’s ice surface. Radar has been used to detect sub-glacial lake in Antarctica since the 1970s and more recently on Mars.
Europa is a better environment to test this because radar can see through ice that has gotten colder. Europa’s surface temperature is typically -170degC because it is so far away from the sun. Europa’s goal is to determine the depth of the ocean that will form when the ice sheet melts. Models predict that it is between 15-25km.
Europa Clipper and Jupiter in the background. NASA/JPL-Caltech
Liquid water could also be located closer to the surface. This would make it easier to reach. Hubble Space Telescope images show plumes erupting in the southern hemisphere. These plumes could be produced like a volcanic eruption, with liquid water rising from the ocean.
Under enough pressure, water will push its way through the fractures and voids in the ice to reach the surface, where it will erupt into geysers. The liquid water which doesn’t make it to surface can still fill cracks and voids in the ice. This is similar to sub-glacial lake formations on Mars and Antarctica.
These features should be found by the missions if they are present. All of this helps to achieve one of the missions’ ultimate goals, which is to find the best place for a future lander that could drill through the ice to reach the mysterious ocean beneath.
Europa’s interior. NASA
Spacecraft traveling near the surface can detect subtle changes in the gravitational fields of an object by using slight variations in rocket speed. These “gravitational abnormalities” are caused when the density of the material beneath the surface of the planet changes as the spacecraft passes overhead.
As an example, a spacecraft can experience a significant extra gravitational pull if it encounters a dense rock in a mountain range. Since many years, gravitational anomalies have been detected on Earth to detect subterranean structures like oil fields, metal deposit and the famous Chixculub impact crater in Mexico.
Europa Clipper and JUICE will be able detect gravitational anomalies, which could allow scientists to discover interesting features on the ocean floor. It is possible that a smooth ocean floor with minor gravitational anomalies could be a boon for the chances of life on the moon.
How to get through the ice
To find out if there is life on Europa we will have to put a lander, possibly carrying a submersible, on the surface one day. This will be difficult even if Europa Clipper or JUICE can identify the thinnest ice.
Europa is very close to Jupiter. This means that spacecraft will need a lot of fuel to be able to escape Jupiter’s gravity and enter an orbit around the moon. JUICE will be the first spacecraft ever to perform the manoeuvre on Ganymede.
The radiation from Jupiter can also damage spacecraft over time. Europa Clipper is therefore designed to stay in long looping orbits around Jupiter, repeatedly removing it from the radiation field. Instead of studying Europa, it will fly by the moon.