THE FUTURE OF OCEAN WORLD EXPLORATION
These robotic explorers could provide vital evidence to answer astrobiology’s greatest questions
1 Europa Clipper
NASA’s next mission beyond the orbit of Mars is the Europa Clipper, succeeding the Juno mission currently at Jupiter. The mission is scheduled to launch in the mid-2020s. The spacecraft will carry nine scientific instruments, each built for a specific purpose, and will conduct a full scan of the surface. It will also utilise icepenetrating equipment in order to characterise Europa’s subsurface ocean.
3 BRUIE
Although this mission is unlikely to see extraterrestrial exploration within the current decade, it has already been tested in Earth’s best analogue location: Antarctica. The buoyancy and manoeuvrability of the Buoyant Rover for Under-Ice Exploration vehicle represents a unique and feasible method of gaining direct insight into subsurface oceans.
2 JUICE
The European Space Agency has also taken a particular interest in the Galilean moons and looks to visit three of them during its three-and-a-halfyear stay. It will arrive at the Jovian system in 2029 and investigate each moon’s environment and the relationship between the three. However, particular emphasis will be on Ganymede.
research regarding an exoplanet’s potential for accommodating liquid water is calculating if a planet resides in its host star’s habitable zone. This is the radius range around a host star where the temperature is perfect for water to exist as a liquid. If the planet orbited any closer the water would evaporate, but if the planet was too far away the water would freeze into ice.
This basic technique is used by astrobiologists when determining if an exoplanet could host liquid water as it’s known that Earth resides in the Sun’s habitable zone. It’s important to remember that this is an extreme simplification and does not take into account things such as a planet’s composition, atmosphere, evolution history and so much more.
To make a discovery of this calibre with great confidence and little uncertainty, the techniques that astrobiologists and astronomers use to detect exoplanets and analyse them will need to be improved in order to infer other aspects of a planet’s properties – this includes its atmosphere. “Astronomers can further their techniques by improving spectral resolution and sensitivity,” says Cable. “This would help us identify possible biosignature molecules in the atmospheres or on the surfaces of exoplanets.”
Recent research suggests that the Milky Way could be littered with ocean worlds. A study led by Quick suggests that out of the 53 exoplanets surveyed, at least 30 of them could be ocean
“An ocean world is any planet, or sometimes moon, that has at least ten times the amount of water that Earth does” Lynnae Quick
worlds, as they fit the assumed parameters. This is based on restricted knowledge, however, as current technologies and techniques allow astronomers to definitively measure an exoplanet’s size, mass and distance from the host star, which can only imply a planet’s surface temperature. “If we see that a planet’s density is lower than Earth’s, that’s an indication that there might be more water there and not as much rock and iron,” Quick says. “But if a planet’s surface temperature is less than 32 degrees Fahrenheit [0 degrees Celsius], where water is frozen, then we have an icy ocean world, and the densities for those planets are even lower.”
With the number of known exoplanets currently over 4,000, Quick’s results could be extrapolated, suggesting that there are thousands of ocean worlds dotted across the Milky Way. Quick also makes the point that there could be other signature signals of ocean worlds that are currently unknown, and that upcoming missions, for example the Europa Clipper mission, will identify these signals.
This could then be applied to exoplanet research in order to identify even more ocean worlds. This could provide greater reliability and accuracy about whether an exoplanet is an ocean world, since it provides something more meaningful than just inferring information based on the planet’s size, mass and density.
Even the recent news regarding Ceres likely being a more mature ocean world could give astronomers new signs and biosignatures to look out for when investigating exoplanets. The study of ocean worlds, both within our Solar System and elsewhere in the cosmos, is certainly one to keep a keen eye on. Through upcoming missions astrobiologists will become even more equipped with highly precise data that could answer one of the most profound questions there is, finally revealing if life on Earth is special or not.