For decades the search for life beyond Earth has followed a familiar idea. Astronomers look for another planet like our own. A rocky world, roughly the same size as Earth, orbiting a star similar to the Sun at just the right distance for liquid water to exist on the surface. That narrow band around a star is often called the habitable zone, and it has shaped the way scientists and the public alike imagine where life might be found in the universe.
But the galaxy may not follow that simple pattern. A much broader picture is emerging as researchers rethink what environments might actually support living systems. Instead of focusing only on Earth-like planets with sunlight and open oceans, attention is increasingly turning toward worlds that are very different from our own.
Recent research published in Nature Astronomy by astrophysicist Gibor Basri explores this wider view of galactic habitability, suggesting that many of the most common environments capable of supporting life may exist beneath thick layers of ice or on larger rocky planets that differ significantly from Earth.
Across our own solar system there are already several worlds that hint at this possibility. Jupiter’s moon Europa is covered in a frozen crust that scientists believe hides a vast ocean beneath the surface. Saturn’s moon Enceladus has become one of the most intriguing objects in the solar system after spacecraft detected powerful plumes of water vapor and ice erupting from cracks near its south pole. Those plumes originate from a salty ocean below the ice.
These discoveries changed how scientists think about where life might exist. Europa and Enceladus are extremely cold at the surface. Sunlight barely reaches them and temperatures plunge far below freezing. Yet beneath their icy shells there may be deep oceans containing liquid water, organic molecules, and energy sources that could support life.
The key to these hidden oceans is internal heat. Moons orbiting giant planets experience strong gravitational forces that stretch and squeeze them as they travel along their orbits. This constant flexing generates heat inside the moon through friction. The process, known as tidal heating, can be powerful enough to keep water in a liquid state beneath the surface even when the exterior remains frozen solid.
Radioactive elements inside a planet or moon can also produce heat for billions of years. Together these internal energy sources can maintain underground oceans that remain stable over immense spans of time.
If environments like these are capable of supporting life, then the number of potential habitats in the galaxy increases dramatically. Ice-covered ocean worlds may be far more common than warm Earth-like planets. Many worlds that appear frozen and lifeless on the outside could conceal vast oceans beneath their surfaces.
Earth itself provides clues that such environments could host living ecosystems. In the deepest parts of our oceans, far beyond the reach of sunlight, life thrives around hydrothermal vents on the seafloor. These vents release mineral-rich water heated by Earth’s interior. Instead of relying on sunlight, microorganisms there obtain energy from chemical reactions involving sulfur and other compounds.
Entire ecosystems have developed around these vents. Bacteria form the base of the food chain, supporting creatures such as tube worms, clams, and crustaceans. The discovery of these deep ocean communities showed that life does not require sunlight to survive. Energy from chemical reactions and internal planetary heat can sustain biological systems even in complete darkness.
If similar conditions exist in the subsurface oceans of icy worlds, it is possible that life could develop there as well. A thick shell of ice above the ocean could even provide protection from radiation and asteroid impacts, creating a stable environment that remains largely unchanged for millions or even billions of years.
The search for life may also need to look beyond planets that match Earth in size. Over the past two decades astronomers have discovered that slightly larger rocky planets known as super-Earths are among the most common worlds in our galaxy. These planets typically range from about one to ten times the mass of Earth.
Super-Earths may offer several advantages for life. Their stronger gravity helps them retain thick atmospheres for long periods of time. A stable atmosphere can regulate climate, maintain liquid water, and shield the surface from harmful radiation.
Larger planets may also hold onto internal heat longer than smaller worlds. This heat can drive geological activity such as volcanism and tectonic movement. These processes recycle nutrients and help maintain chemical balance within oceans and atmospheres, conditions that may be important for sustaining life over long periods.
Another factor shaping the potential for life is the type of star a planet orbits. Our Sun will remain stable for roughly ten billion years before it begins to run out of fuel. That has been long enough for life to emerge on Earth, but some stars in the galaxy burn far more slowly and last much longer.
Stars slightly smaller than the Sun can shine for tens of billions of years. Planets orbiting these stars could have enormously long periods in which life might arise and evolve. Given enough time, biological systems could develop complexity far beyond what we see on Earth today.
The history of the galaxy itself also influences where life might appear. Early in the Milky Way’s existence, heavy elements such as carbon, oxygen, and iron were relatively scarce. These elements are created inside stars and spread through space when stars explode or shed their outer layers. Over billions of years this process enriched the galaxy with the materials needed to form rocky planets and complex chemistry.
As more generations of stars lived and died, the amount of heavy elements increased, making it easier for planetary systems to form. The modern Milky Way is far richer in the ingredients required to build Earth-like planets and other rocky worlds.
This gradual enrichment suggests that the potential for life in the galaxy has changed over time. Earlier eras may have had fewer suitable planets, while later periods could see many more worlds capable of supporting living systems.
Taken together, these ideas point toward a major shift in how scientists think about life in the universe. The search is expanding beyond the narrow concept of Earth-like planets orbiting Sun-like stars. Instead, researchers are considering a wide range of environments that could support biology.
Many of these environments may not resemble the familiar landscapes of Earth. They may exist in dark oceans hidden beneath kilometers of ice. Others may be large rocky planets with thick atmospheres and deep global oceans. Some could orbit stars that will shine steadily for tens of billions of years.
The Milky Way contains hundreds of billions of stars. Around those stars orbit vast numbers of planets and moons. If hidden oceans and super-Earth planets are common among them, the number of potential habitats for life may be enormous.
Some of those worlds may already host living systems that remain completely invisible to us. Their biospheres would be sealed away beneath frozen surfaces, detectable only through subtle chemical signatures or plumes of material escaping from cracks in the ice.
Exploration within our own solar system may soon provide the first direct answers. New missions are preparing to study icy moons such as Europa in unprecedented detail. Scientists hope to analyze the chemistry of the moon’s surface and investigate the ocean believed to exist beneath the ice.
If even simple life is discovered in one of these hidden oceans, it would transform humanity’s understanding of the universe. It would show that life does not require a planet identical to Earth. Instead, living systems could arise wherever water, energy, and stable conditions come together.
That realization would greatly expand the range of places where life might exist. Worlds once dismissed as too cold or too distant could suddenly become prime targets in the search for living systems beyond Earth.
Humanity has long imagined discovering another Earth somewhere among the stars. But the universe may hold a far greater variety of living environments than we once believed. The most common homes for life may not lie under blue skies and warm sunlight. They may exist in silent oceans hidden beneath ice, scattered across countless worlds throughout the galaxy.
Source:Â
Basri, G. (2026). A broad perspective on galactic life.
Nature Astronomy.
