GJ 1132 b
A nearby rocky exoplanet with disputed atmospheric detections.
GJ 1132 b (also called Gliese 1132 b) is an exoplanet that orbits the red dwarf star GJ 1132, 41 light-years away in the constellation Vela. It was discovered using the MEarth-South array in Chile. The planet has been described as one of the most significant exoplanets found outside the Solar System, largely because its closeness to Earth was expected to let telescopes analyze its atmosphere, measure wind speeds, and even determine the color of its sunsets—assuming it had one.
The planet's diameter is about 13% larger than Earth's, and its mass is roughly 1.6 times that of Earth, suggesting a rocky composition similar to our own. It orbits its star every 1.6 days at a distance of 2.24 million kilometers (1.4 million miles). Because its parent star is small—only 20% the diameter of the Sun—the effect of the planet's transits on the star's light is amplified, making atmospheric studies more feasible.
GJ 1132 b receives 19 times more stellar radiation than Earth does. Its equilibrium temperature is estimated at 529 K if it has an Earth-like albedo, or 409 K with a Venus-like albedo. The planet is likely hotter than Venus, especially if an atmosphere exists, which would raise surface temperatures further.
Multiple claims about the planet's atmosphere have been made and later challenged. In April 2017, a hydrogen-dominated atmosphere was reported, but more precise work ruled that out. In 2021, a hazy hydrogen atmosphere—without helium but containing methane and hydrogen cyanide, implying about 8.9% free nitrogen—was claimed. However, two subsequent studies found no evidence of molecular absorption in the Hubble Space Telescope's WFC3 spectrum; instead, the spectrum appeared flat and featureless, consistent with an airless rock.
A secondary eclipse observed by the James Webb Space Telescope, published in 2024, measured a substellar temperature of 709 K—only slightly below the maximum possible dayside temperature of 746 K (assuming zero albedo and no heat redistribution). The thermal emission spectra rule out pure-carbon dioxide atmospheres above 0.006 bar and pure-water vapor atmospheres above 0.16 bar. Consequently, GJ 1132 b likely has little to no atmosphere, aligning with the Cosmic shoreline concept seen in other hot rocky M-dwarf planets such as LHS 3844 b (Kuakua), GJ 1252 b, TRAPPIST-1b and c, GJ 367b (Tahay), and GJ 486b (Su).
Quick Facts
- Discoverer
- MEarth-South Array Team
- Discovery Site
- Chile
- Discovered
- May 10, 2015 (announced) November 12, 2015 (confirmed)
- Discovery Method
- Transit
- Apsis
- astron
- Eccentricity
- 0.0118 · 0.047 · 0.0099
- Star
- GJ 1132
Facts from the source article.
Lore & Background
GJ 1132 b was discovered by the MEarth-South array in Chile. Its parent star has a diameter only 20% that of the Sun, which increases the effect of the planet's transits on the star's light. The planet receives 19 times more stellar radiation than Earth and is likely hotter than Venus, with higher temperatures prevailing at the surface if an atmosphere exists.
Multiple claims about the detection of an atmosphere have been made and subsequently disputed. In April 2017, a hydrogen-dominated atmosphere was claimed, but later more precise work ruled that out. In 2021, a hazy hydrogen atmosphere without helium but with methane and hydrogen cyanide (implying substantial free nitrogen at about 8.9% of the atmosphere) was claimed. However, two subsequent studies found no evidence for molecular absorption in the HST WFC3 spectrum, which appeared flat and featureless, consistent with an airless rock.
A secondary eclipse observed by the James Webb Space Telescope and published in 2024 revealed a substellar temperature of 709 K, only slightly below the maximum possible dayside temperature of 746 K (assuming zero albedo and no heat redistribution). The thermal emission spectra rule out pure-carbon dioxide atmospheres above 0.006 bar and pure-water vapor atmospheres above 0.16 bar, indicating the planet likely has little to no atmosphere, consistent with the Cosmic shoreline concept seen in other hot rocky M-dwarf planets.
Reader's Guide
GJ 1132 b's significance lies in its role as a test case for atmospheric characterization of rocky exoplanets around red dwarfs. Its proximity and the small size of its host star made it a prime target for transmission spectroscopy, leading to multiple—and conflicting—claims of atmospheric detection. The eventual ruling out of a thick atmosphere, based on a flat spectrum from HST and thermal emission data from JWST, places it among a growing class of airless or nearly airless hot rocky worlds orbiting M-dwarfs, such as LHS 3844 b, GJ 1252 b, TRAPPIST-1b and c, GJ 367b, and GJ 486b. The planet's equilibrium temperature (529 K for an Earth-like albedo, 409 K for a Venus-like albedo) and high stellar radiation (19 times Earth's) underscore the difficulty of retaining an atmosphere under such conditions. The 2024 JWST secondary eclipse provided the most stringent constraints, ruling out even thin CO₂ and water vapor atmospheres, and supporting the idea that many close-in rocky planets around red dwarfs are stripped of their atmospheres by stellar activity. This makes GJ 1132 b a key object in understanding the Cosmic shoreline—the boundary between planets that retain atmospheres and those that do not.
Did You Know?
- A 2024 JWST secondary eclipse measured a substellar temperature of 709 K.
- Multiple atmospheric detections have been claimed and later ruled out, with the spectrum appearing flat and featureless.
More in Transiting Exoplanets, Part 3 1-24
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