TESS Discovery of an ultra-short-period planet around the nearby M dwarf LHS 3844 (1809.07242v1)

Abstract: Data from the newly-commissioned \textit{Transiting Exoplanet Survey Satellite} (TESS) has revealed a "hot Earth" around LHS 3844, an M dwarf located 15 pc away. The planet has a radius of $1.32\pm 0.02$ $R_\oplus$ and orbits the star every 11 hours. Although the existence of an atmosphere around such a strongly irradiated planet is questionable, the star is bright enough ($I=11.9$, $K=9.1$) for this possibility to be investigated with transit and occultation spectroscopy. The star's brightness and the planet's short period will also facilitate the measurement of the planet's mass through Doppler spectroscopy.

Discovery of an Ultra-Short-Period Planet Around the M Dwarf LHS 3844

The paper entitled "Discovery of an Ultra-Short-Period Planet Around the Nearby M Dwarf LHS 3844" discusses the detection and characterization of a terrestrial exoplanet orbiting a nearby M dwarf star. Utilizing data from the Transiting Exoplanet Survey Satellite (TESS), this research highlights the discovery of a "hot Earth" exoplanet, denoted LHS 3844\,b, which orbits its host star very closely, with a period of just 11 hours, positioning it in the category of ultra-short-period (USP) planets.

Findings and Methodology

The primary findings of the paper detail that LHS 3844\,b has a radius of 1.32 times that of Earth ($R_\oplus$) and that its host star, LHS 3844, is an M dwarf located 15 parsecs away, possessing a mass and radius of approximately 15% and 19% of the solar values, respectively. The proximity of the star and the high brightness in the infrared bands ($I=11.9$, $K=9.1$) make it an ideal candidate for detailed follow-up studies, including mass measurement through Doppler spectroscopy and atmospheric characterization through transit and occultation techniques.

TESS observed LHS 3844 as part of its wide-sky survey, utilizing high-cadence imaging data to identify transit events. Ground-based observations and spectroscopy further validated these findings, ruling out alternative explanations such as stellar variability and background binary contamination. The lack of substantial radial velocity variation from CHIRON and CORALIE spectrographs suggests a low planetary mass, with an upper limit of 0.96 $M_\oplus$, which is consistent with a terrestrial composition for the detected exoplanet.

Implications and Future Studies

The detection of LHS 3844\,b adds to the growing list of known USP planets, and it provides a compelling target for atmospheric studies, given its large transit depth and proximity to Earth. The planet's equilibrium temperature, estimated at about 805 K, raises intriguing questions about the retention of an atmosphere, given the likelihood of photoevaporation processes in such close orbiting bodies. This characteristic places LHS 3844\,b as an outlier in typical population statistics of exoplanets, particularly for those smaller than 2 $R_\oplus$, a region in the size distribution commonly analyzed for atmospheric loss.

The paper emphasizes that the TESS mission is particularly equipped for finding and characterizing such systems, given its observation strategy that favors nearby M dwarfs, which typically host planets with larger transit depths relative to solar-type stars. Future missions and instruments with advanced spectroscopic capabilities will be crucial in fully characterizing the atmospheric properties of LHS 3844\,b, providing deeper insights into the formation and evolution of USP planets.

Further research focusing on LHS 3844\,b, particularly in measuring its mass with greater precision, could refine its density and thus offer stronger constraints on its composition. Continued monitoring to detect potential atmospheric features could elucidate the processes governing the survival and structure of atmospheres in extreme conditions.

In conclusion, this discovery solidifies the efficacy of TESS and similar telescopes in expanding the catalog of terrestrial planets around nearby stars. The paper demonstrates the ongoing potential for deriving significant astrophysical insights from the detection of transiting exoplanets, pushing forward our understanding of planetary systems around M dwarfs.