Using the Immersion GRating INfrared Spectrometer (IGRINS) at the Gemini South Observatory on Cerro Pachon, Chile, astronomers have measured carbon-to-hydrogen (C/H) and oxygen-to-hydrogen (O/H) abundance ratios in the atmosphere of the hot-Jupiter exoplanet WASP-77Ab.
An artist’s impression of a hot-Jupiter exoplanet. Image credit: Sci-News.com.
WASP-77Ab is a tidally-locked gas giant about 1.2 times larger and 1.8 times more massive than Jupiter.
It orbits the moderately bright G8-type star WASP-77A once every 1.36 days.
Otherwise known as TOI-398, BD-07 436A, and TYC 4697-201-1, the system is located 344 light-years away in the constellation of Cetus.
“WASP-77Ab is a type of exoplanet called a hot Jupiter because they are like our Solar System’s Jupiter, but with a temperature upwards of 1,093 degrees Celsius (2,000 degrees Fahrenheit),” said Arizona State University’s Dr. Michael Line and colleagues.
The astronomers then focused on measuring the composition of WASP-77Ab’s atmosphere to determine what elements are present, compared with the star it orbits.
“Because of their sizes and temperatures, hot Jupiters are excellent laboratories for measuring atmospheric gases and testing our planet-formation theories,” they said.
“We needed to try something different to address our questions. And our analysis of the capabilities of Gemini South indicated that we could obtain ultra-precise atmospheric measurements.”
Illustration of how information about the atmosphere of WASP-77Ab is extracted from the observations. Image credit: P. Smith / M. Line / S. Selkirk / ASU.
Using the IGRINS instrument at the Gemini South Observatory, the researchers observed the thermal glow of WASP-77Ab as it orbited its host star.
From this instrument, they gathered information on the presence and relative amounts of different gases in its atmosphere.
With clear measurements of both water and carbon monoxide in the atmosphere of WASP-77Ab, they were able to estimate the atmospheric C/H (0.35х solar) and O/H (0.32x solar) abundances and the corresponding atmospheric carbon-to-oxygen ratio (C/O = 0.59; the solar value is 0.55).
“These amounts were in line with our expectations and are about the same as the host star’s,” Dr. Line said.
“This work represents a pathfinder demonstration for how we will ultimately measure biosignature gases like oxygen and methane in potentially habitable worlds in the not-too-distant future.”
The results were published in the journal Nature.
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M.R. Line et al. 2021. A solar C/O and sub-solar metallicity in a hot Jupiter atmosphere. Nature 598, 580-584; doi: 10.1038/s41586-021-03912-6
