TRAPPIST-1g
TRAPPIST-1g — A Potentially Habitable World
Located approximately 40 light-years from Earth in the constellation Aquarius, TRAPPIST-1g is a rocky, Earth-sized exoplanet orbiting an ultracool red dwarf star. It is one of seven confirmed planets in the TRAPPIST-1 system and lies towards the outer region of the star's habitable zone.
TRAPPIST-1g is slightly larger and more massive than Earth, with a calculated surface gravity approximately 104% of Earth's. Its physical characteristics make it an interesting candidate for investigating whether distant rocky worlds could support environments suitable for liquid water.
However, the planet receives only around a quarter of Earth's incoming stellar energy. Whether it possesses an atmosphere capable of maintaining sufficiently warm surface temperatures remains unknown.
The TRAPPIST-1 Planetary System
TRAPPIST-1 is an ultracool red dwarf star approximately 40 light-years from Earth. With only around 9% of the Sun's mass, it is considerably smaller, cooler and less luminous than our own star.
Seven confirmed rocky planets orbit TRAPPIST-1, all travelling much closer to their parent star than Mercury orbits the Sun.
TRAPPIST-1g is the seventh planet from the star, orbiting between TRAPPIST-1f and TRAPPIST-1h. Alongside TRAPPIST-1e and TRAPPIST-1f, it is commonly identified as occupying the system's habitable zone, although the precise boundaries depend on atmospheric and climate assumptions.
Studying these neighbouring planets allows astronomers to investigate how differences in stellar radiation, atmospheric evolution and planetary composition influence the potential for habitability.
The TRAPPIST-1 Planetary System (artist's impression).
The Discovery of TRAPPIST-1g
The TRAPPIST-1 planetary system was first identified in 2016 by an international team led by Belgian astronomer Michaël Gillon at the University of Liège.
Using the TRAPPIST-South telescope at the European Southern Observatory's La Silla Observatory in Chile, researchers initially identified planets through the transit method, detecting small reductions in starlight as planets passed in front of their host star.
Further observations, particularly with NASA's Spitzer Space Telescope, revealed seven planets, announced in February 2017.
TRAPPIST-1g attracted scientific interest because of its rocky composition, Earth-like surface gravity and position near the outer edge of the habitable zone.
Subsequent measurements of planetary transits and gravitational interactions have refined its mass, radius and orbital characteristics.
Size, Mass and Physical Characteristics
TRAPPIST-1g has a radius approximately 113% that of Earth and a mass around 132% of Earth's.
Its calculated surface gravity is approximately 1.04 g, meaning an individual would experience gravitational forces only slightly stronger than on Earth.
Its average density, approximately 5.1 g/cm³, is consistent with a predominantly rocky composition, potentially including an iron-rich core and silicate mantle.
Although these measurements suggest a terrestrial planet, scientists have not directly observed its surface or internal structure.
Whether TRAPPIST-1g possesses mountains, oceans, extensive ice deposits, active geology or a magnetic field remains unknown.
Its relatively Earth-like gravity makes it particularly interesting when considering the physical requirements of possible future human habitation, although gravity alone cannot establish whether the planet could support people.
Orbit and Tidal Locking
TRAPPIST-1g completes one orbit around its parent star every 12.35 Earth days, at a distance of approximately 7 million kilometres (0.0468 AU).
Despite orbiting much closer to its star than Earth does to the Sun, the planet receives only around 25% of Earth's incoming stellar radiation.
TRAPPIST-1g is expected to be tidally locked, meaning one hemisphere may experience permanent daylight while the opposite remains in darkness.
The boundary between these hemispheres is known as the terminator.
If the planet possesses a substantial atmosphere, atmospheric circulation could transport heat between its illuminated and dark hemispheres, potentially moderating temperature differences.
Without sufficient atmospheric heat redistribution, its surface could experience extreme temperature variations.
Atmosphere and Climate
Whether TRAPPIST-1g possesses an atmosphere remains one of the most important unanswered questions about the planet.
Its relatively low incoming stellar energy means that atmospheric greenhouse warming could be particularly important for maintaining liquid water on the surface.
An atmosphere containing suitable concentrations of greenhouse gases, potentially including carbon dioxide, could theoretically increase surface temperatures.
However, atmospheric composition, pressure and long-term stability remain unknown. An airless environment has not been excluded.
TRAPPIST-1 is also an active red dwarf star. Stellar flares and high-energy radiation may influence atmospheric evolution, although the extent to which TRAPPIST-1g has retained any atmosphere remains uncertain.
Future telescope observations will be essential for investigating these possibilities.
Water, Oceans and Ice
Artist's impression.
TRAPPIST-1g lies near the outer region of its star's habitable zone, where suitable atmospheric conditions could potentially allow liquid water to exist.
Because the planet receives considerably less stellar energy than Earth, a substantial greenhouse effect may be necessary to prevent widespread freezing.
Climate models of tidally locked planets suggest that atmospheric circulation could transport heat across the surface, potentially influencing the distribution of ice and any liquid water.
Depending on atmospheric pressure, composition and available water, possible environments include extensive ice-covered regions, frozen oceans or areas where greenhouse warming permits liquid water.
Internal geological heating could also influence the behaviour of water beneath an icy surface.
However, no oceans, surface water or ice deposits have been directly detected on TRAPPIST-1g.
The Search for Life
TRAPPIST-1g is an important candidate for investigating the conditions under which rocky planets might support life.
Its Earth-like surface gravity, predominantly rocky composition and position near the outer habitable zone make it scientifically interesting.
However, its comparatively low stellar energy introduces additional questions about whether sufficiently warm surface environments could develop.
Scientists are particularly interested in whether the planet possesses a stable atmosphere, liquid water and the chemical ingredients necessary for biological activity.
Potential atmospheric biosignatures, including combinations of gases such as oxygen and methane, could eventually provide clues about biological processes, although non-biological explanations would also need to be investigated.
No evidence of life has been detected on TRAPPIST-1g.
The James Webb Space Telescope
The James Webb Space Telescope (JWST), developed through cooperation between NASA, the European Space Agency (ESA) and the Canadian Space Agency (CSA), is helping astronomers investigate the TRAPPIST-1 planetary system.
Using infrared spectroscopy, scientists can analyse changes in starlight as planets pass in front of their host star, searching for possible atmospheric absorption features.
Webb has collected observations of all seven TRAPPIST-1 planets, including TRAPPIST-1g.
However, no atmosphere has been confirmed around TRAPPIST-1g, and atmospheric analysis remains challenging because of interference from the host star's activity.
Observations of neighbouring planets are also providing important comparisons, helping researchers understand how atmospheric conditions may vary across the system.
Further observations and improved analytical techniques could help determine whether TRAPPIST-1g possesses an atmosphere and what its composition might reveal about potential habitability.
European Contributions to TRAPPIST-1 Research
European astronomers played a leading role in discovering the TRAPPIST-1 planetary system.
The initial discovery was led by Belgian astronomer Michaël Gillon and researchers at the University of Liège, using the TRAPPIST-South telescope at the European Southern Observatory's La Silla site in Chile.
Further international observations established the existence of seven planets, announced in February 2017.
European scientists continue contributing to planetary modelling, atmospheric investigations and the interpretation of James Webb observations.
ESA also participates in Webb's scientific operations and instrumentation. Its future PLATO and Ariel missions will expand our understanding of exoplanets and atmospheric chemistry, although neither is specifically designed to investigate TRAPPIST-1g.
These efforts are helping researchers investigate how rocky planets develop and whether suitable atmospheric environments can survive around small red dwarf stars.
The Future of TRAPPIST-1g Research
Future investigations will focus on determining whether TRAPPIST-1g retains an atmosphere and whether greenhouse warming could create environments suitable for liquid water.
Continued observations with the James Webb Space Telescope may help constrain atmospheric composition and improve models of the planet's climate.
Scientists will also compare TRAPPIST-1g with its neighbouring planets, particularly TRAPPIST-1e and TRAPPIST-1f, to understand how different levels of stellar radiation influence atmospheric evolution.
Its Earth-like gravity makes it particularly interesting for research into the physical conditions that could eventually support human habitation.
However, atmospheric pressure, temperature, radiation exposure, available water and breathable air would all need to be understood before its suitability for humans could be assessed.
Although direct spacecraft exploration remains beyond current capabilities, continued astronomical observations could significantly improve our understanding of this distant world.
2nd November 2026 — TRAPPIST-1g Atmospheric Research
The James Webb Space Telescope has collected observations of TRAPPIST-1g as part of its wider investigation of the seven-planet system.
Researchers continue examining whether rocky planets around TRAPPIST-1 can retain atmospheres despite the star's activity.
TRAPPIST-1g's atmosphere remains unconfirmed. Its measured mass and radius indicate a rocky world with gravity close to Earth's, while its location towards the outer habitable zone makes atmospheric greenhouse warming particularly important when assessing potential surface habitability.
Last reviewed: 2nd November 2026