From ocean moons in our solar system to rocky planets around distant stars, science has identified compelling candidates. Explore each one below.
Enceladus shoots jets of ocean water directly into space, allowing spacecraft to sample its subsurface sea without landing. Those samples contain hydrogen, organic molecules, and silica nanoparticles — fingerprints of active hydrothermal vents on the ocean floor.
Europa conceals a global liquid water ocean twice the volume of all Earth's oceans beneath a cracked ice shell, with evidence of hydrothermal activity — making it one of the most promising places to search for life in the solar system.
One of seven rocky planets orbiting the ultra-cool red dwarf TRAPPIST-1, planet e sits squarely in the habitable zone and is considered the most likely of the system's worlds to support liquid water — it receives almost exactly the same amount of energy from its star as Earth does from the Sun.
Dubbed "Earth's older cousin," Kepler-452b is a super-Earth orbiting a Sun-like star at almost the same distance as Earth orbits our Sun — and its star is about 1.5 billion years older, meaning any life there has had far longer to evolve than life on Earth.
The closest known exoplanet to Earth orbits our nearest stellar neighbor in the habitable zone — meaning liquid water could exist on its surface. But its host star is a violent red dwarf that regularly blasts the planet with powerful flares, raising serious questions about whether any atmosphere could survive.
Titan is the only world beyond Earth with stable liquid on its surface — though that liquid is methane and ethane, not water. Its thick nitrogen atmosphere and rich organic chemistry raise the tantalizing possibility of life based on completely different biochemistry.
The largest moon in the solar system, Ganymede has its own magnetic field and a deep subsurface ocean estimated to hold more liquid water than all of Earth's oceans combined — though it sits sandwiched between layers of ice rather than contacting a rocky seafloor.
Once covered in liquid oceans, Mars harbors subsurface water ice, seasonal methane spikes, and minerals that sustained life on early Earth — making it the most studied candidate in astrobiology.
The outermost of Jupiter's Galilean moons, Callisto likely hosts a subsurface saltwater ocean and — crucially — sits outside Jupiter's intense radiation belts, making it the most radiation-safe of the potentially ocean-bearing moons and a candidate for future human bases.
While Venus's surface is a hellscape of 465 °C and crushing pressure, its cloud layer at 48–60 km altitude has Earth-like temperature and pressure — and in 2020, a controversial detection of phosphine sparked intense debate about possible aerial microbial life.
The largest object in the asteroid belt surprised NASA's Dawn spacecraft with bright salt deposits revealing ancient briny water reservoirs, organic molecules on its surface, and possibly a residual liquid layer — making this small world a modest but intriguing astrobiology target.