Confirmed exoplanet · Database record + computed analysis
GJ 667 C c
A confirmed world orbiting GJ 667 C, 23.6 light-years away.
A super-Earth
1.77 Earth radii. Worlds between Earth and Neptune in size are the most common in the galaxy, yet our Solar System has none, which is why each one matters.
The orbit
Its year, one full orbit, takes just 28.1 Earth days.
Temperature and starlight
It receives 0.88 times Earth's starlight, the same order as our own world.
Its sun
Its star is a red dwarf (3,350 K surface), type M1.5 V: small, dim, flare-prone, and destined to outlive the Sun many times over. The system holds 3 stars, so its skies have more than one sun. It shares the system with 4 other known planets.
How far is that, really?
At 24 light-years, tonight's light from this system left it around the year 2002. That is close by galactic standards, which makes it a prime target for follow-up telescopes. A Voyager-speed probe would need roughly 418,016 years to get there.
How we found it
It was found by the radial-velocity method: the planet's gravity swings its star in a small circle, and that wobble shows up as a rhythmic Doppler shift in the starlight. The wobble's size gives the planet's minimum mass. The discovery was announced in 2013 from La Silla Observatory.
Everything above is computed from the archive’s measured values for this planet. Where a quantity is missing, the statement is omitted rather than guessed.
The deep dive
Researched for the Atlas from Wikipedia — Gliese 667 Cc (6,644 characters read) · updated Sep 20, 2026
01 A World in a Triple-Star System
Gliese 667 Cc does not orbit a single sun — it circles a star that is itself part of a three-star family. Its host, Gliese 667 C, is a red dwarf with only 0.31 times the Sun's mass and 0.42 times its radius. The two more massive companions, Gliese 667 A and B, share the same system roughly 23.62 light-years from Earth — about 223.5 trillion kilometres — in the constellation Scorpius. From the planet's surface, those two companion stars would appear as extremely bright points of light in the sky, far outshining anything visible from Earth's night sky, yet providing relatively little warmth compared to the nearby red dwarf overhead. The parent star Gliese 667 C radiates only 1.4 percent of the Sun's luminosity, and its surface temperature is a relatively cool 3,700 K, compared to the Sun's 5,778 K. Its age is poorly constrained, with estimates placing it at greater than two billion years old — leaving a wide margin of uncertainty that affects predictions about the system's long-term stability and any potential for life.
02 How the Planet Was Found
Gliese 667 Cc was discovered using the radial velocity method, sometimes called the Doppler method. As the planet orbits its star, its gravitational pull causes the star to wobble slightly toward and away from Earth. That motion compresses and stretches the wavelengths of light reaching our telescopes — a measurable Doppler shift in the star's spectrum. The discovery was first announced in a pre-print made public on 21 November 2011 by the European Southern Observatory's High Accuracy Radial Velocity Planet Searcher group, known as HARPS. A peer-reviewed journal report followed on 2 February 2012, produced by researchers at the University of Göttingen and the Carnegie Institution for Science, independently backing the HARPS group's findings. This two-step confirmation — pre-print followed by refereed publication from a separate team — gave the discovery unusually solid standing early in its history. The planet is sometimes described as the first confirmed potentially habitable exoplanet, a distinction that reflects how significant its detection felt at the time of announcement.
03 Size and Mass of a Super-Earth
Gliese 667 Cc belongs to the category astronomers call super-Earths — worlds more massive and larger than Earth, but still well below the scale of ice giants like Uranus and Neptune. Its minimum mass is approximately 3.7 Earth masses, a lower bound set by the geometry of the radial velocity technique, which can only measure the component of a star's wobble directed along our line of sight. The planet's expected radius is around 1.5 Earth radii, though that estimate depends heavily on assumptions about composition. A rockier planet would be denser and smaller for a given mass; a world with more ice or volatiles would puff out to a larger radius. Neither the true mass nor the radius has been directly measured, so both figures carry significant uncertainty. The equilibrium temperature — calculated assuming the planet radiates away as much energy as it absorbs, with no greenhouse effect factored in — is estimated at 277.4 K, equivalent to 4.3 degrees Celsius or about 39.6 degrees Fahrenheit, close to the freezing point of water.
04 An Orbit Measured in Weeks
Gliese 667 Cc sits extremely close to its star compared to the Earth-Sun distance. Its semi-major axis is just 0.1251 astronomical units — roughly one-eighth of the Earth-Sun distance — and it completes one full orbit in only 28.155 Earth-days, less than a single calendar month. Despite this tight orbit, the planet lies near the inner edge of its star's habitable zone, because Gliese 667 C is so much dimmer than the Sun. The planet receives about 90 percent of the total electromagnetic energy that Earth receives from the Sun based on the host star's bolometric luminosity. However, a substantial fraction of that radiation arrives in the infrared part of the spectrum, invisible to human eyes. This matters because infrared photons interact differently with atmospheres and surfaces than visible light does, complicating direct comparisons with Earth's energy budget when assessing potential habitability.
05 The Star as Seen from the Surface Deeper
Standing on the surface of Gliese 667 Cc and looking up, the host star would appear noticeably larger in the sky than our Sun does from Earth. Gliese 667 C would subtend an angular diameter of 1.24 degrees — 2.3 times the visual diameter of the Sun as seen from Earth's surface. In terms of visual area, it would appear 5.4 times larger than the Sun appears to us. Yet despite this imposing size, the star would still occupy only 0.003 percent of the planet's full sky sphere, or 0.006 percent of the visible sky when positioned directly overhead. Its color would skew strongly toward deep orange and red rather than the pale yellow-white of our Sun. Because red dwarfs emit very little ultraviolet light, the planet's surface would receive minimal ultraviolet radiation, which has complex implications: lower UV flux could reduce the formation of certain prebiotic molecules that some researchers believe were important for the origin of life on Earth, while simultaneously sparing the surface from one form of radiation damage.
06 Orbital Chaos and Shifting Eccentricity Deeper
Gliese 667 Cc does not travel a stable, unchanging ellipse around its star. Gravitational interactions with the other planets in the system render its orbit dynamically unstable over time. The eccentricity of the orbit — a measure of how stretched or circular the path is — oscillates on a cycle of approximately 4.6 years, swinging between 0.06 and 0.28 in one range and between 0.05 and 0.25 in another, according to simulations. This is not a small variation: at maximum eccentricity the planet swings noticeably closer to and farther from its star during each 28-day orbit, causing significant fluctuations in the energy it receives. Simulations modeling the planet as having a terrestrial-style rocky mantle also suggest it is caught in a 3:2 or higher spin-orbit resonance, meaning it rotates on its axis a fixed number of times for every orbit completed — a configuration maintained by the same tidal forces that shape its eccentric path.
07 Tidal Heating: A Planet Cooking From Within Deeper
Perhaps the most dramatic finding about Gliese 667 Cc is the intensity of tidal heating it experiences. A 2013 paper revealed that tidal heating on the planet is 300 times greater than what Earth experiences from the Moon and Sun combined. This energy comes from the continuous flexing of the planet's interior as its eccentric orbit brings it alternately closer to and farther from Gliese 667 C. Simulations give the tidal energy flux of Gliese 667 Cc as 10 to the power of 26.7 joules per year — compare this to Gliese 667 Cb, the inner planet, at 10 to the power of 23.7 joules per year. The consequence is severe: this energy input is predicted to raise the planet's temperature by 1.6 Kelvin every one hundred thousand years, causing at least partial melting of the mantle and very likely resulting in a completely molten mantle. The simulations suggest Gliese 667 Cc would rapidly become a lava-covered world, its surface perpetually resurfaced by volcanic outpourings.
08 Tidal Locking and the Terminator Zone
Because Gliese 667 Cc orbits so close to its star, it is likely tidally locked — the same hemisphere permanently faces the star, just as the Moon always shows the same face to Earth. One side of the planet would bake in perpetual starlight, while the opposite side sits in permanent darkness and extreme cold. Between these two extremes lies a narrow band called the terminator line, where the star hangs perpetually near the horizon. At the terminator, temperatures might hover around 273 K, or 0 degrees Celsius — the freezing point of water — creating at least a theoretical sliver where liquid water could persist. If the planet has a sufficiently thick atmosphere, circulation could carry heat from the dayside to the nightside, potentially expanding the habitable region significantly. Both the terminator zone scenario and the thick-atmosphere scenario remain speculative, however, and the intense tidal heating described elsewhere makes the overall habitability picture considerably more pessimistic than early assessments suggested.
09 Where It Ranks on Habitability Indexes
The Planetary Habitability Laboratory, a research group that tracks and ranks potentially habitable worlds, listed Gliese 667 Cc as the fourth-most Earth-like exoplanet located in the conservative habitable zone of its parent star as of July 2018. Its equilibrium temperature of 277.4 K places it slightly warmer than Earth's equivalent figure of 254.3 K, and therefore slightly closer to the hot inner edge of the habitable zone. The gap between those two temperatures reflects how much closer Gliese 667 Cc sits to the inner boundary compared to Earth's more central position in the Sun's habitable zone. These rankings are based on how Earth-like a planet appears by measurable parameters, but critics note that such rankings do not capture the full complexity of habitability — particularly the tidal heating and orbital dynamics that may make conditions on Gliese 667 Cc far harsher than the simple temperature comparison implies.
10 A Long-Lived Star, But Not a Safe Haven
Red dwarfs like Gliese 667 C burn their fuel so slowly that they are expected to live for 100 to 150 billion years — roughly 10 to 15 times longer than the Sun's projected lifespan of about 10 billion years. On the surface, this might seem like an enormous advantage for any life trying to establish itself and evolve. A 2017 paper challenged this optimism by applying Bayesian inference to the question. If Earth is assumed to be typical of a habitable planet, the statistical argument shows there must be some constraint that prevents habitability and the evolution of life on planets orbiting stars less massive than 0.65 solar masses. Gliese 667 C has a mass of only 0.31 solar masses — well below that threshold. The paper's conclusion is that the probability of habitability around such a low-mass star may be considerably smaller than estimates based purely on Earth-similarity metrics would suggest, even accounting for the star's extraordinary longevity.
11 How Many Planets Actually Orbit Gliese 667 C? Deeper
The number of confirmed planets around Gliese 667 C has been a moving and contested figure. Claims have been made for as many as seven planets in the system, a number that would have made it one of the richest nearby planetary systems known. However, the article notes that those additional planets may be artifacts — the result of failing to properly account for correlated noise in the radial velocity data. Radial velocity measurements are sensitive to stellar activity such as starspots and convective motions, which can mimic or mask planetary signals if not carefully modeled. After scrutiny, only two planets are currently considered confirmed in the system. Gliese 667 Cc is described as the second confirmed planet out from the star, orbiting toward the inner edge of the habitable zone. The reduction from seven candidates to two confirmed worlds illustrates a broader challenge in exoplanet science: distinguishing real planetary signals from the complex, correlated variability of active stars.
12 Observing the System from Earth
Gliese 667 C has an apparent magnitude of 10.25, making it far too faint to see with the naked eye under any conditions. Even a small telescope cannot easily pick it out, because its light is overwhelmed by the combined glare of its two brighter companions, Gliese 667 A and B, which share the same field of view. The star's absolute magnitude is approximately 11.03. The system lies in the constellation Scorpius, which is well placed for observers in the southern hemisphere and low northern latitudes during summer months, but the faintness of the C component means that detecting any signal from the planet itself — rather than from the star's spectrum — remains beyond the reach of current observational technology. All known properties of Gliese 667 Cc have been inferred indirectly through the radial velocity technique, and no direct imaging of the planet has been achieved.
About this record
The measured values come from the NASA Exoplanet Archive, and any missing value has not been determined yet; the Atlas never fills gaps with guesses. More standout worlds: Proxima b, TRAPPIST-1e, K2-18 b, 55 Cancri e, and the detection methods that found them all.