Astronomers from Johns Hopkins University (JHU) used the James Webb Space Telescope (JWST) to observe a giant exoplanet known as HATS-75 b. This exoplanet is one of the recently discovered Giant Exoplanets orbiting M-dwarf Stars (GEMS). It was discovered in 2021 with the help of Automated Telescope Network-South (HATSouth) and NASA's Transiting Exoplanet Survey Satellite (TESS). This exoplanet is at a distance of some 637 light-years.
Astronomers have already learned various aspects of the exoplanet, but recently, they observed it again to know more about its atmosphere. The recent analysis was done by a team of astronomers led by JHU's Reza Ashtari. They investigated the chemical composition of HATS-75 b's atmosphere.
"Our observations offer an opportunity not only to characterise the atmospheric composition of HATS-75 b, but also to explore how stellar heterogeneity influences the interpretation of transmission spectra in low-mass star systems," they wrote in the paper, quoted by phys.org.
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Using the NIRSpec PRISM instrument, the astronomers observed three transits of HATS-75 b. The biggest takeaway is that the star HATS-75 is a bit "messy." It has starspots (cool, dark patches) and faculae (hot, bright patches).
When the planet passes in front of the star, these spots change the colour of the light passing through the planet's atmosphere. This is called the Transit Light Source (TLS) effect.
Initially, it looked like the planet was hazy, but the researchers realised it was actually just the star's spots "contaminating" the data.
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What's in the Atmosphere?
The researchers found a strong signal of methane and the presence of Carbon Dioxide (CO2) and Carbon Monoxide (CO). When it comes to water, it's surprisingly hard to find. It's likely there, but the "noise" from the star is masking its signature.
A "Low-Metal" Giant
In astronomy, metallicity refers to any element heavier than Hydrogen or Helium. HATS-75 b has a very strange chemical makeup. Its air is mostly Hydrogen and Helium, with very few heavy elements. It has a high Carbon-to-Oxygen (C/O) ratio. The planet's deep interior seems to have many more metals than its outer atmosphere.
"HATS-75 b thus joins the rare population of giant planets around M-dwarfs observed with JWST, underscoring both the challenges of stellar contamination in transmission spectroscopy and the importance of careful host-star treatment in revealing the true chemistry of these uncommon worlds," the scientists conclude.
