Detection of the atmosphere of the 1.6 Earth mass exoplanet GJ 1132b (1612.02425v2)

Abstract: Detecting the atmospheres of low-mass low-temperature exoplanets is a high-priority goal on the path to ultimately detect biosignatures in the atmospheres of habitable exoplanets. High-precision HST observations of several super-Earths with equilibrium temperatures below 1000K have to date all resulted in featureless transmission spectra, which have been suggested to be due to high-altitude clouds. We report the detection of an atmospheric feature in the atmosphere of a 1.6 Mearth transiting exoplanet, GJ 1132b, with an equilibrium temperature of ~600K and orbiting a nearby M dwarf. We present observations of nine transits of the planet obtained simultaneously in the griz and JHK passbands. We find an average radius of 1.43 +/- 0.16 Rearth for the planet, averaged over all the passbands, and a radius of 0.255 +/- 0.023 Rsun for the star, both of which are significantly greater than previously found. The planet radius can be decomposed into a "surface radius" at ~1.375 Rearth overlaid by atmospheric features which increase the observed radius in the z and K bands. The z-band radius is 4sigma higher than the continuum, suggesting a strong detection of an atmosphere. We deploy a suite of tests to verify the reliability of the transmission spectrum, which are greatly helped by the existence of repeat observations. The large z-band transit depth indicates strong opacity from H2O and/or CH4 or a hitherto unconsidered opacity. A surface radius of 1.375 +/- 0.16 Rearth allows for a wide range of interior compositions ranging from a nearly Earth-like rocky interior, with ~70% silicate and ~30% Fe, to a substantially H2O-rich water world.

• The paper presents high-precision transmission spectroscopy over nine transits to detect and measure GJ 1132b's atmospheric opacity.
• It finds an increased planetary radius in the z and K bands, indicating the potential presence of water and methane.
• The results underscore the value of multi-wavelength analysis for refining atmospheric characterization and directing future infrared observations.

Detection of the Atmosphere of the Exoplanet GJ 1132 b

The paper presents a comprehensive analysis of the detection of an atmospheric feature in the exoplanet GJ 1132 b, a significant find given the planet's low mass of 1.6 Earth masses and its status as an exoplanet orbiting a nearby M dwarf star. By utilizing high-precision observations over several transits using both optical and near-infrared passbands, the authors offer valuable insights into the physical and atmospheric properties of GJ 1132 b.

Key Findings and Methodology

The authors detail the use of transmission spectroscopy to deduce the characteristics of the atmosphere surrounding GJ 1132 b. This technique involved the analysis of multi-band photometry data acquired from nine transits, allowing for the measurement of the planetary radius as a function of wavelength. By solving for the transit light curves without empirical biases related to stellar calibrations, the paper found the planetary radius to be larger than previously reported.

The analysis illustrated that the exoplanet has a surface radius of approximately 1.375 R⊕ with an increased radius in the z and K bands, suggesting an atmosphere that could potentially contain H$_2$O and/or CH$_4$. The z-band radius, significantly higher than the continuum, proposes strong atmospheric opacity, a factor explored through theoretical models.

Implications for Exoplanetary Atmospheres

Detecting atmospheric features in low-mass exoplanets such as GJ 1132 b is critical in advancing the understanding of exoplanetary atmospheres, particularly for planets orbiting M dwarfs. The presence of water and methane in GJ 1132 b's atmosphere hints at potential chemical processes taking place, which could broaden research into the atmospheric dynamics of terrestrial exoplanets.

From a planetary science perspective, the ability to detect and analyze the atmospheric composition of planets like GJ 1132 b could drive new methodologies in the search for biosignatures. The observations and subsequent analyses underscore the importance of multi-wavelength studies in yielding insight into atmospheric compositions.

Future Directions and Technological Advances

The findings encourage subsequent observations, particularly in the infrared spectrum using instruments like HST/WFC3 and future missions with JWST. Such observations could provide enhanced data regarding molecular signatures, further elucidating atmospheric compositions and conditions. The research also implies that instruments capable of finer spectral resolution at various wavelengths could refine the transmission spectral data, overcoming current limitations in precision and depth analysis.

In conclusion, the paper marks a meaningful contribution to the ongoing paper of exoplanetary atmospheres, particularly for low-mass planets. By refining observational techniques and advancing theoretical modeling efforts, scientific communities can better interpret atmospheric signatures and assess their potential habitability, paving the way for future discoveries in exoplanet science.