In fact, the environment in these oceans is very similar to the environment of the earth at the time when life began
Cross-section through the outer region of Europa's south polar region showing ice caps, the fractured ice cap, the liquid water ocean (cloudy at the base near hydrothermal vents) and the rocky interior. NASA/JPL 
A lander on Europa uses a probe to melt a hole in the ice, then unleashes a swarm of swimming robots. Conceptual impression, not to scale. Nasa/JPL-Caltech 
A hydrothermal vent on the floor of the North East Pacific Ocean. A substrate of tube worms that feed on chemosynthesizing microbes covers the base. NOAA/PMEL 
Self-contained robotic microswimmers, deployed from a component that penetrated the icy crust of a moon containing a subsurface ocean. Not to scale. NASA/JPL
NASA recently announced $600,000 in funding to research the feasibility of sending swarms of tiny swimming robots (called autonomous microswimmers) to explore oceans beneath the ice caps of our solar system's many "ocean worlds." But don't imagine metallic humanoids swimming like frogs underwater They will probably be simple triangular wedges - the equivalent of the primordial materials from which life was created.
Pluto is an example of a world that probably has oceans. But the worlds with oceans that are closest to the surface and therefore most accessible are Europa, a moon of Jupiter, and Enceladus, a moon of Saturn.
These oceans interest scientists not only because they contain so much liquid water (Europa's ocean probably has about twice as much water as all of Earth's oceans), but because chemical reactions between rocks and ocean water can support life. In fact, the environment in these oceans is very similar to the environment of the earth at the time when life began.
These are environments where water that has seeped into the rock of the ocean floor becomes hot and chemically enriched - water that is then released into the ocean. Microbes can feed on this chemical energy, and be eaten by larger organisms. No sunlight or atmosphere is actually needed. Many of these hot rocky structures, called "hydrothermal vents," have been documented on Earth's ocean floor since they were discovered in 1977. In these places the local food web is indeed supported by chemosynthesis (energy from chemical reactions) and not photosynthesis (energy from sunlight).
On most oceanic worlds in our solar system, the energy that heats their rocky interiors and keeps the oceans from freezing to the base comes mostly from oceans. This is in contrast to the heating of the interior of the earth which is mostly radioactive. But the chemistry of the interactions between the water and the rock is similar.
Enceladus' ocean has already been sampled by the Cassini spacecraft flying through plumes of ice crystals ejected through cracks in the ice, and it is hoped that NASA's Europa Clipper mission may find similar plumes to sample when it begins a series of close flybys of Europa in 2030. But entering the ocean to study it You'll potentially gather a lot more information than just sniffing a freeze-dried sample.
This is where the concept of sensing using independent micro-swimmers comes into play. The idea is to land on Europa or Enceladus (which won't be cheap or easy) in a place where the ice is relatively thin (not yet located) and use a radioactively heated probe to melt a 25 cm wide hole down to the ocean - which is hundreds or thousands of meters below.
When the probe gets there, it will release up to fifty 12cm wedge-shaped micro-swimmers to explore. Their endurance will be far less than that of the 3.60-foot-long autonomous underwater vehicle called Boaty McBoatface, with a range of 2,000 km that has already cruised more than From a hundred kilometers under the Antarctic ice.
More of the topic in Hayadan:
