For most of human history, Earth was the only known example of a habitable world. Even after astronomers discovered planets orbiting other stars in the 1990s, those early finds were often bizarre: giant gas planets skimming dangerously close to their stars, nothing like the familiar terrain beneath our feet. Then, in the mid-2000s, a new class of planet emerged from the data – worlds larger than Earth but smaller than Neptune.
Astronomers called them Super-Earths. Despite the dramatic name, Super-Earths are not necessarily lush paradises or superior versions of our own planet.
The term refers only to their size and mass. They typically weigh between two and ten times the mass of Earth, making them the most common kind of planet discovered in our galaxy.
Ironically, our own solar system contains none. Several astronomers have remarked that Nature seems to prefer making super-Earths and yet we don’t have one in our own solar system.
This realization, that the most common worlds in the galaxy are absent from our cosmic neighbourhood, has reshaped our understanding of planet formation. The first super-earth discovery changed everything The turning point came in 2004, when astronomers using telescopes in Chile discovered a planet orbiting the nearby red dwarf star Gliese 876.
This planet, Gliese 876d, was about seven times the mass of Earth. It wasn’t a gas giant. It wasn’t a tiny rocky planet either.
It was something in between, the first clear example of a Super-Earth. Astronomer Eugenio Rivera, one of the scientists involved in the discovery, later recalled the excitement of realizing they had found something entirely new. What stood out was not just the planet itself, but the realization that such worlds might be common.
This was not a one-off curiosity; it was a glimpse of a population. Also Read | What comets and asteroids reveal about life, death and the unknown In the years that followed, the Kepler Space Telescope, launched in 2009, transformed this trickle of discoveries into a flood. Kepler monitored more than 150,000 stars, looking for tiny dips in brightness caused by planets passing in front of them.
Many of those dips belonged to Super-Earths. Story continues below this ad By 2013, NASA scientists announced that Super-Earth-size planets were among the most common types of planets in the Milky Way. The most striking result is just how common small planets are.
What are super-earths actually like? Super-Earths can vary enormously. Some are rocky, like Earth, but larger. Others may be covered by deep global oceans.
Some may have thick atmospheres of hydrogen and helium, resembling miniature versions of Neptune. Gravity on these worlds would feel very different.
A person standing on a Super-Earth might weigh twice or three times what they do on Earth. Mountains could be flatter, crushed under their own weight.
The atmosphere, if present, might be thicker and denser. In some cases, Super-Earths orbit extremely close to their stars, where temperatures reach hundreds or thousands of degrees.
These would be hostile environments, with molten surfaces and vaporized rock. Story continues below this ad Yet others lie in the so-called habitable zone, where temperatures could allow liquid water to exist. A planet that captured the world’s Imagination One of the most famous Super-Earths is Kepler-452b, discovered in 2015.
It orbits a star very similar to our Sun and lies in its habitable zone. NASA scientists described it as one of the closest analogues to Earth ever found.
Also Read | Space junk menace: How it could crash into our future tech Though Kepler-452b lies about 1,400 light-years away, far beyond the reach of any spacecraft, its existence changed how scientists think about Earth’s uniqueness. It suggested that planets capable of supporting Earth-like conditions may not be rare exceptions.
A surprise in our stellar backyard Perhaps even more exciting was the discovery of Proxima Centauri b in 2016 – a Super-Earth orbiting the nearest star to the Sun, just 4. 24 light-years away.
Story continues below this ad Astronomer Guillem Anglada-Escudé, who led the discovery, described the emotional moment when the data finally revealed the planet’s presence. After years of observations and careful analysis, the signals aligned.
The nearest star had a planet. For the first time in human history, astronomers could point to a nearby star and say with confidence: there is a potentially rocky world there. This discovery sparked renewed interest in future interstellar missions.
Though current spacecraft would take tens of thousands of years to reach it, proposed technologies, such as laser-propelled probes, could shorten that journey dramatically. Why super-earths matter for the search for life Super-Earths may be among the best places to search for life beyond Earth.
Their larger size gives them stronger gravity, which helps them retain atmospheres, a crucial ingredient for stable climates and liquid water. The James Webb Space Telescope, launched in 2021, is now studying the atmospheres of some Super-Earths. By analyzing starlight passing through those atmospheres, scientists can detect molecules such as water vapour, carbon dioxide, or methane.
These measurements could reveal whether any of these worlds possess conditions suitable for life. Story continues below this ad A universe filled with possibilities The discovery of Super-Earths has fundamentally changed humanity’s view of the universe.
Once, we believed our solar system was a template for all others. Now we know it is only one of many possibilities. Also Read | After the Big Bang: How the first stars lit up our universe Billions of Super-Earths likely orbit stars across the Milky Way.
Some may be barren, others ocean-covered, and a few perhaps resembling Earth in ways we are only beginning to imagine. These distant worlds remind us that Earth is not the only way for a planet to exist.
The galaxy is filled with variation, creativity, and surprise. And somewhere among those countless Super-Earths, there may be skies, oceans, and landscapes waiting to be discovered. Shravan Hanasoge is an astrophysicist at the Tata Institute of Fundamental Research.