Evidence of water vapor detected in the atmosphere of Smertrios

Using the CARMENES spectrograph, astronomers have found evidence of water vapor in the atmosphere of a hot Saturn exoplanet designated HD 149026 b, dubbed Smertrios. The finding, reported in a research paper published on the preprint server arXiv, could be key to a better understanding of the structure and formation scenario of this alien world.

Smertrios is a metal-rich hot Saturn orbiting HD 149026—a yellow subgiant star of spectral type G0 IV, at a distance of some 248.5 light years. The planet has a radius of about 0.81 Jupiter radii and is approximately three times less massive than Jupiter. Previous observations have found that Smertrios orbits its host every 2.876 days, about 0.043 AU from it. The planet's equilibrium temperature is estimated to be 1,693 K.

The team of astronomers led by Sayyed A. Rafi of the University of Tokyo in Japan employed CARMENES at the Calar-Alto Observatory to conduct high-resolution cross-correlation spectroscopy of Smertrios. Their main aim was to get more insights into the composition of this exoplanet's atmosphere.

"Transmission spectroscopy presents one of the most successful approaches for investigating the atmospheres of exoplanets. We analyzed the near-infrared high-resolution transmission spectrum of a hot Saturn, HD 149026 b, taken using CARMENES spectrograph," the researchers wrote in the paper.

By analyzing the CARMENES data, Rafi's team found evidence of a water signal very close to the expected location of Smertrios. The strongest signal had a signal-to-noise (S/N) ratio of 4.8. The astronomers noted that the detected signal could only be regarded at the moment as evidence of water vapor existence, not a confirmed detection.

According to the study, the evidence of water vapor in the atmosphere of Smertrios suggests that the planet's carbon to oxygen ratio must be less than one if the atmosphere is homogeneous and at chemical equilibrium, as the hydrogen cyanide abundance is expected to be very low.

Although the researchers searched for hydrogen cyanide in the atmosphere of Smertrios, they found no evidence of this compound. The astronomers assume that this may be due to the relatively low S/N dataset. Therefore, the possibility of hydrogen cyanide in the atmosphere of this planet cannot be definitively excluded.

The study also measured the orbital and rest velocities of Smertrios, which were found to be approximately 158.17 and 2.57 km/s, respectively. However, it was noted that while the orbital velocity is consistent with the expected value, the rest velocity is highly red-shifted. The authors of the paper concluded that this might be explained by several scenarios, such as anomalous atmospheric dynamics or an orbit with non-zero eccentricity.

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