Water is essential for life as we know it, and the search for it in our solar system has been a top priority for scientists for decades. Beyond Earth, the discovery of water—whether in liquid, ice, or vapor form—could provide crucial clues about the potential for life elsewhere and the history of our planetary neighborhood. Recent findings from various space missions have revealed that water is more common in the solar system than once believed, hiding in places we least expected.
The quest to find water beyond Earth has led scientists to explore a diverse range of environments across the solar system. From the frozen moons of Jupiter and Saturn to the craters of the Moon and Mercury, evidence of water has been popping up in some of the most inhospitable regions. These discoveries are reshaping our understanding of where life could potentially exist and how planets and moons have evolved over billions of years.
Recent missions, like NASA’s Perseverance rover on Mars, the Juno spacecraft orbiting Jupiter, and the Cassini mission around Saturn, have contributed to our growing knowledge of water in the solar system. These findings not only deepen our understanding of planetary geology but also bring us one step closer to answering the fundamental question: Is there life elsewhere in our solar system?
Water on Mars: subsurface reserves and seasonal flows
Mars has long been a focus of the search for water. Once home to vast lakes and rivers, the Red Planet has dried out over the past few billion years, but evidence suggests that water may still exist beneath its surface. In 2020, data from the European Space Agency’s Mars Express mission revealed evidence of a large subsurface lake beneath the planet’s southern polar ice cap. This discovery has raised hopes that liquid water might be more abundant underground than previously thought, potentially harboring microbial life in these dark, cold reservoirs.
Additionally, seasonal flows, also known as recurring slope lineae, have been detected on the Martian surface, which appear as dark streaks that ebb and flow with the Martian seasons. These features have been linked to briny water, which could form when underground ice melts or when salts on the surface absorb moisture from the thin Martian atmosphere. While the exact nature of these flows is still under investigation, their presence suggests that Mars continues to have some form of active water cycle.
Icy Moons of Jupiter and Saturn: oceans beneath the surface
Some of the most exciting discoveries of water in the solar system have come from the icy moons of Jupiter and Saturn, particularly Europa, Ganymede, and Enceladus.
Europa, one of Jupiter’s largest moons, is thought to have a vast subsurface ocean beneath its icy crust. The Hubble Space Telescope has detected plumes of water vapor erupting from cracks in Europa’s surface, indicating that this ocean may be in direct contact with the moon’s rocky core, potentially creating the right chemical conditions for life. NASA’s upcoming Europa Clipper mission, set to launch in the 2030s, will study these plumes in greater detail and assess Europa’s habitability.
Similarly, Saturn’s moon Enceladus has shown strong evidence of a global subsurface ocean beneath its icy shell. The Cassini spacecraft discovered water vapor and ice particles being ejected from geysers near Enceladus’s south pole, indicating that the moon’s interior is geologically active. These plumes contain organic molecules, which could suggest that hydrothermal activity at the ocean floor provides the energy necessary to support life.
Jupiter’s largest moon, Ganymede, also harbors a massive underground ocean, detected by the Galileo spacecraft in the 1990s and confirmed by recent observations from the Hubble Space Telescope. Ganymede’s magnetic field and auroras suggest that a thick layer of salty water exists beneath its surface ice, making it another prime candidate in the search for life.
Water ice on the Moon and Mercury
The Moon and Mercury, despite being airless and exposed to extreme temperatures, have shown surprising evidence of water. In 2009, NASA’s LCROSS mission confirmed the presence of water ice in the permanently shadowed craters at the Moon’s poles. These craters never receive sunlight, allowing water molecules, likely delivered by comets or retained from volcanic activity, to remain frozen for billions of years. The Artemis program, NASA’s new initiative to return humans to the Moon, will focus in part on exploring these polar regions to assess their potential as resources for future lunar missions.
Mercury, the closest planet to the Sun, might seem an unlikely candidate for water, but its poles tell a different story. The MESSENGER spacecraft found evidence of ice in permanently shadowed craters at Mercury’s north pole, similar to those on the Moon. Despite the planet’s proximity to the Sun, these regions are cold enough to trap water ice, protected from solar radiation by deep crater walls.
Comets and asteroids: ancient water reservoirs
Comets have long been considered frozen time capsules from the early solar system, made up of ice and dust that have remained unchanged for billions of years. When comets approach the Sun, their ice vaporizes, forming the iconic tails we see from Earth. Recent missions, like the Rosetta spacecraft, which orbited and landed on Comet 67P/Churyumov–Gerasimenko, have provided unprecedented insight into the water content of comets. Rosetta found that the water on 67P is chemically different from Earth’s water, suggesting that comets may not have been the primary source of water for our planet.
Asteroids, once thought to be mostly dry, are also proving to be reservoirs of water. NASA’s Dawn mission found evidence of hydrated minerals on the dwarf planet Ceres, indicating that it may have once had a subsurface ocean. More recently, the OSIRIS-REx mission, which collected samples from the asteroid Bennu, found that Bennu’s rocks contain water-bearing minerals, suggesting that water was present in the early solar system and may have played a role in the formation of planets and moons.
Conclusion: a solar system rich in water
The discovery of water in various forms across the solar system has profound implications for the search for life beyond Earth. From the subsurface oceans of icy moons to the ancient ice on comets and asteroids, water is more widespread than we ever imagined. Future missions to Mars, Europa, Enceladus, and beyond will continue to explore these findings, bringing us closer to answering one of humanity’s greatest questions: Are we alone in the universe?
