It had been called "one of the most important planets ever discovered beyond the Solar System": Due to its relative proximity to Earth, telescopes should have been able to determine the composition of its atmosphere, the speed of its winds and the color of its sunsets,[9][10][11] if an atmosphere was present. This is due in part to the small diameter of its parent star (20% that of the Sun), which increases the effect on the star's light of itstransits. The planet's diameter is approximately 20% larger than that of the Earth[1] and its mass is estimated at 1.6 times that of Earth,[2] implying that it has an Earth-likerocky composition.[12] GJ 1132 b orbits its star every 1.6 days at a distance of 1.4 million miles (2.24 million kilometres).[8]
The planet receives 19 times morestellar radiation than Earth.[1] Theequilibrium temperature is estimated at 529 K (256 °C; 493 °F) for an Earth-likealbedo, or 409 K (136 °C; 277 °F) for a Venus-like albedo. The planet is likely to be hotter than Venus, as higher temperatures likely prevail at the surface if the planet has an atmosphere.[12]
GJ 1132b has been subject to multiple claims about the detection of an atmosphere. In April 2017, a hydrogen-dominated atmosphere was claimed to have been detected around GJ 1132 b.[13][6] However, subsequent, more precise work ruled out the claim.[14] Instead, in 2021 detection of a hazy hydrogen atmosphere without helium but with the admixturemethane andhydrogen cyanide (implying substantial underlying freenitrogen in the mix, at around 8.9% of the atmosphere) was claimed.[15] However, two subsequent studies found no evidence for molecular absorption in the HST WFC3 Spectrum of GJ 1132 b. Instead, the spectrum was found to be flat,[16][17] which is more consistent with our current understanding ofphotoevaporation.[citation needed]
A secondary eclipse observed by theJames Webb Space Telescope and published in 2024 revealed a substellar temperature of709±31 K (436 °C; 817 °F). This is only slightly below the maximum possible dayside temperature of746+11 −14K (473 °C; 883 °F), assuming a zero albedo planet with no heat redistribution. The thermal emission spectra rules out pure-carbon dioxide atmospheres above 0.006 bar and pure-water vapor atmospheres above 0.16 bar.[4] Therefore, GJ 1132b likely has little to no atmosphere, consistent with the idea of the "Cosmic Shoreline"[4] and similar to other hot rocky M-Dwarf planets includingLHS 3844 b (Kua'kua),[18]GJ 1252 b,TRAPPIST-1b[19] andc,[20]GJ 367b (Tahay), andGJ 486b (Su).[21]
^abcdefgXue, Qiao; Bean, Jacob L.; Zhang, Michael; Mahajan, Alexandra S.; Ih, Jegug; Eastman, Jason D.; Lunine, Jonathan I.; Mansfield, Megan Weiner; Coy, Brandon P.; Kempton, Eliza M.-R.; Koll, Daniel D.; Kite, Edwin S. (2024). "JWST Thermal Emission of the Terrestrial Exoplanet GJ 1132b".arXiv:2408.13340.
^Mansfield, Megan Weiner; Xue, Qiao; Zhang, Michael; Mahajan, Alexandra S.; Ih, Jegug; Koll, Daniel; Bean, Jacob L.; Coy, Brandon Park; Eastman, Jason D.; Kempton, Eliza M.-R.; Kite, Edwin S.; Lunine, Jonathan (2024). "No Thick Atmosphere on the Terrestrial Exoplanet GI 486b".arXiv:2408.15123.
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