Have you ever been curious about the existence of planets that are larger than Earth but smaller than monsters like Neptune? These unique exoplanets are known as Super-Earths.
Though there is no super-Earth in our solar system, NASA and its global counterparts have found out that these worlds are among the most frequent types of planets in the Milky Way galaxy.
What is a Super-Earth?
The term Super-Earth refers to a category of exoplanet that is defined largely by its mass, and sometimes also by its radius. A super-Earth is more massive than Earth, but less so than Neptune (approximately 17 times more massive than Earth) and Uranus (around 14 times more massive than Earth), whose respective masses are in the same range as the mass of the super-Earth.
It is important to note that the term “Super-Earth” acts as a planetary classification based only on the size and mass of a planet and does not imply the presence of water or conditions that suit human life.
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Parameter
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Astronomical Data
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Category
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Exoplanet (planet orbiting a star outside our solar system)
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Mass Range
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Roughly 1 to 10 times Earth's mass (some studies extend this up to 20 Earth masses)
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Radius Range
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Commonly cited as 1.5 to 2 times Earth's radius (extend up to 4 Earth radii)
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Composition
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Can be rocky, water-rich, snowball worlds, or dense gas mixtures
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Solar System Equivalent
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None (No super-Earth exists in our solar system)
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Key Observatory Missions
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NASA Kepler, TESS, and the James Webb Space Telescope (JWST)
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The Difference Between Super-Earths and Mini-Neptunes
Exoplanets with a mass between around 2 and 10 Earth masses, astronomers often have a problem defining the exact boundaries of the planets in this mass range:
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Super-Earths: Commonly have a rocky surface with a thin or reasonable atmosphere over it.
Mini-Neptunes (Sub-Neptunes): These are planets that are just above the mass/radius limit which is characterized by being covered with a rich envelope of hydrogen and helium gas. They do not possess a rocky surface and are considered miniature gas giants.
The scientists themselves accept that there is still some debate on this boundary. NASA data from the Kepler mission indicates there is a "gap" with respect to the planet's size around 1.5-2 Earth radii, which is called the Fulton Gap (or radius valley). Scientists use it to statistically differentiate between rocky super-Earths and gas-rich mini-Neptunes.
Extreme Environments and Climates of Super-Earths
Super-Earths’ climate characteristics are highly extreme due to the variable temperatures and proximity of their stars. Such planets experience extremely high surface temperatures that can melt rocks and turn metals into rainfall.
Certain super-Earths that orbit red dwarf stars have one hemisphere stuck in incessant bright sunlight while the other side is permanently dark and cold.
One idea is that some planets may be completely submerged underwater and totally blanketed by a hydrogen-rich atmosphere. This is still only a hypothesis, existing in the hopes of being proven by identifying this planet class by means of spending our time gathering JWST data.
Important Facts About Super-Earths
A Gap in the Solar System
Although they are prevalent in the universe, super-Earths are nowhere to be found in our Solar System which has a void between Earth (the Earth being the biggest terrestrial planet) and Uranus (the smallest gas giant planet).
Extreme Surface Gravity
The gravity of a rocky super-Earth may be a much stronger force than its Earth counterpart, depending on its density and composition due to its size.
Super-Earths in Our Universe
The first discovered exoplanets were two super-Earths with masses of 3.9 and 4.3 times more than that of Earth which were announced by astronomers Aleksander Wolszczan and Dale Frail in 1992, inventing the new field of astronomy. The first planet orbiting a star similar to the Sun (51 Pegasi B) was discovered in 1995.
First Exoplanet Discovery (1992)
The first observation confirming the existence of two exoplanets (weighing 3.9 and 4.3 times as much as Earth) orbiting the PSR B1257+12 pulsar by astronomers Wolszczan and Dale Frail took place. This was before another discovery of an exoplanet orbiting a star similar to the Sun in 1995 (51 Pegasi b).
Cancri 55 e: The "Diamond Planet" Fable
This super-Earth which has a radius that is approximately double that of Earth, revolves around its star at an exceedingly close distance (with temperatures on the surface reaching more than 2,000° Celsius).
K2-18b and the Question of Bio-Indicators
This sub-Neptune/super-Earth-class planet made the news when methane and carbon dioxide were found in its atmosphere by the JWST (2023), which made scientists believe that it could be a "Hycean" world.
Later in 2025, a tentative signal was claimed that a gas which is known to be a product of biological activities on Earth. Evidence suggests that K2-18b is a suitable target for future studies. However, the "sign of life" claim remains unconfirmed and is still disputed.