English (UK)
GJ 436 b is a Neptune-like exoplanet that orbits very close to its star, a red dwarf cooler and smaller than the Sun. This proximity exposes the planet to the star's activity, causing part of its atmosphere to escape and form an extensive "tail" that accompanies it in its orbit.
This behavior has sparked great interest in the scientific community, especially due to the possibility of studying the composition of its atmosphere. Models predict the presence of molecules such as water vapor and methane, but so far these signals have not been detected.
To address these unknowns, a new study led by the IAA-CSIC, as part of the doctoral thesis of researcher Alberto Peláez Torres and with the collaboration of the CARMENES consortium, has used high-resolution observations with the CARMENES and CRIRES⁺ spectrographs. Thanks to this approach, the most precise values to date for cloud pressure and atmospheric metallicity of GJ 436 b have been obtained.
“Our results show that the clouds are located around the millibar level, that is, in a very high region of the atmosphere, and that the metallicity reaches about 900 times that of the Sun,” says Alberto Peláez, a researcher at the IAA-CSIC and leader of the study. He adds: “We also believe we have reached the limit of precision with which we can determine the altitude of the clouds. Even by combining data from multiple nights of observation, we were unable to improve the measurement. This is probably because the clouds themselves block or attenuate the water absorption signals in that region of the atmosphere, making it difficult to detect them more accurately.”
UNDERSTANDING THE ABSENCE OF DETECTABLE MOLECULES
Until now, the lack of detections of molecules such as water vapor and methane could be due to GJ 436 b's atmosphere being covered by a very high cloud layer that blocks the observation of the gases, or to the atmosphere being too dense, which attenuates molecular signals. Precisely determining the altitude of these clouds and the atmospheric metallicity is crucial to understanding why current instrumentation has failed to detect the expected molecules and, at the same time, provides key information for advancing the study of Neptune-like and sub-Neptune planets.
The results of this work represent a significant advance in the characterization of small exoplanet atmospheres. The combination of high-resolution infrared observations from CARMENES and CRIRES⁺ has overcome some limitations of previous studies and provides a more robust framework for future research on atmospheric composition and cloud formation on other exoplanets.
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An artist's rendering of "The Behemoth," a massive, comet-like cloud of hydrogen ejected from a hot, Neptune-sized planet located just 30 light-years from Earth. The parent star, a faint red dwarf called GJ 436, is also shown. Hydrogen is being evaporated from the planet due to the star's extreme radiation. Credits: NASA, ESA, and G. Bacon (STScI) |
The work was carried out entirely at the Institute of Astrophysics of Andalusia (IAA-CSIC), where the data analysis, model development, and results interpretation took place. Furthermore, the study is part of the CARMENES high-resolution spectrograph consortium, located at the Calar Alto Observatory and scientifically managed by the IAA-CSIC.
Having an atmosphere is a key characteristic for understanding the nature and evolution of a planet, although it doesn't necessarily imply that it can harbor life. Studying its composition allows us to reconstruct the physical and chemical processes that have shaped these worlds since their formation. In this work, we analyzed the atmosphere of an extremely hot planet—with temperatures close to 700 degrees Celsius—located very close to its star, conditions that make it uninhabitable, but especially valuable for testing current models of planetary evolution.
“Thanks to advances in instrumentation and astronomical analysis techniques, the possibility of characterizing these atmospheres with an unprecedented level of detail is becoming tangible,” explains Alberto Peláez (IAA-CSIC). “These studies aim to shed light on the formation and evolution of relatively small planets, such as Neptunes and sub-Neptunes, the most abundant in the universe and which, until now, have resisted being characterized.”
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Planetary atmosphere models indicate that any world with the usual mixture of hydrogen, carbon, and oxygen, and a temperature up to 1,000 Kelvin, should have a large amount of methane and a small amount of carbon monoxide. This planet, called GJ 436b, has a temperature of about 800 Kelvin; it was expected to have methane, but observations from the Spitzer Space Telescope (NASA) showed that it does not. This demonstrates the diversity of exoplanets and the need to revise exoplanetary atmosphere models. Credit: NASA/JPL-Caltech/R. Hurt (SSC/Caltech) |
The Calar Alto Observatory is one of the infrastructures that belong to the national map of Unique Scientific and Technical Infrastructures (Spanish acronym: ICTS), approved on March 11th, 2022, by the Science, Technology and Innovation Policy Council (CPCTI).
CONTACTS:
The Institute of Astrophysics of Andalusia- P. Amado
COMMUNICATION - CALAR ALTO OBSERVATORY