Jan 04, 2024 - In a scientific odyssey exploring the cosmos, the James Webb Space Telescope (JWST) has brought to light the enigmatic world of GJ 367b, a sub-Earth orbiting a red dwarf star. Led by a team of researchers including Michael Zhang from the University of Chicago, the study utilized the Mid-Infrared Instrument (MIRI) on the JWST to scrutinize the mid-infrared phase curve of this celestial body, unraveling unprecedented details about its composition, atmosphere, and orbital dynamics.

GJ 367b stands out in the vast expanse of space as a hot and exceptionally dense sub-Earth, presenting a myriad of characteristics that challenge our understanding of rocky planets in orbit around M dwarfs. With a scorching temperature of 1370 K and a density of 10.2 ± 1.3 g cm−3, this sub-Earth completes its orbit around its M dwarf host star in a mere 0.32 days. The swift orbit and intense heat create a harsh environment, prompting scientists to delve into the intricacies of this peculiar exoplanet.

The observed eclipse depth of 79 ± 4 parts per million (ppm) and a nightside planet-to-star flux ratio of 4 ± 8 ppm provide crucial insights into the thermal characteristics of GJ 367b. These measurements, along with a relative phase amplitude of 0.97 ± 0.10, collectively suggest a planet with a zero-albedo and no heat recirculation—a stark departure from the patterns observed in many other exoplanets.

The emission spectrum, a treasure trove of information about the planet's atmosphere, unveils a blackbody with minimal heat redistribution and a low albedo of approximately 0.1. However, one must approach this revelation with caution, as an anomalous wavelength bin has been identified, attributed to unexplained systematics. Despite this anomaly, the emission spectrum serves as a crucial tool, placing constraints on potential atmospheric compositions.

The absence of day-night heat recirculation rules out the possibility of 1 bar atmospheres for a wide range of compositions, while 0.1 bar atmospheres remain consistent with the observational data. Combining this data with the inference that a substantial portion of the dayside is molten, the researchers propose that GJ 367b likely experienced significant volatiles loss, shaping its current atmospheric and surface properties.

The study delves into the broader question of the habitability of small rocky planets orbiting M dwarfs, a topic of immense significance in the search for extraterrestrial life. The unique challenges posed by M dwarf stars, characterized by their small radii and low luminosity, make studying their planetary atmospheres a tantalizing prospect. The research team emphasizes the importance of understanding the impact of high-energy radiation, stellar flares, and prolonged pre-main-sequence phases on planetary atmospheres.

GJ 367b, discovered by the Transiting Exoplanet Survey Satellite (TESS), emerges as an observational gem due to its favorability for study by the JWST. Its properties make it a prime candidate for advancing our understanding of sub-Earths and their place in the cosmos. The study suggests that small rocky planets, like GJ 367b, may follow distinct formation channels, leading to diverse outcomes in atmospheric and surface characteristics.

The exceptional density of GJ 367b, measured at 10.2 ± 1.3 g cm−3, raises intriguing possibilities regarding its origin. The researchers speculate that this sub-Earth could be a remnant of a more massive planet whose silicate mantles evaporated away. Another intriguing hypothesis posits that GJ 367b formed through a process akin to the creation of Mercury, involving a giant impact that stripped the mantle, leaving the iron core behind.

Thermal emission, a crucial tool in probing the surface and atmosphere of rocky planets, is leveraged by the research team to unravel the mysteries of GJ 367b. Drawing parallels with previous observations of super-Earths and mini-Neptunes, the researchers utilize the second-order phase curve model to fit the data, ensuring a comprehensive and data-driven analysis.

The study highlights the role of tidal heating due to the planet's eccentricity, providing a potential explanation for the observed delay of 45 ± 13 seconds in the eclipse compared to the transit plus half the orbital period. The calculated eccentricity of e cos ω = 0.0027 ± 0.0008 aligns with expectations, considering the presence of non-transiting outer companions with high eccentricities.

As the researchers embark on a journey to unravel the mysteries of GJ 367b, the study raises essential questions about the broader implications of such findings. With the JWST continuing its mission to explore the cosmos, GJ 367b joins the ranks of exoplanets that offer valuable insights into the diverse range of planetary systems. These discoveries not only expand our knowledge of exoplanets but also provide crucial benchmarks for calibrating atmospheric mass loss models.

In the coming years, as technology advances and observational capabilities improve, scientists anticipate unraveling more secrets hidden within the atmospheres and surfaces of distant worlds. GJ 367b, with its dark, hot, and airless demeanor, serves as a testament to the power of space exploration and the thirst for knowledge that drives humanity's quest to understand the mysteries of the universe.

Source - ARXIV