The chemical abundances of exoplanet atmospheres may provide valuable information about the bulk compositions , formation pathways , and evolutionary histories of planets .
Exoplanets which have large , relatively cloud-free atmospheres , and which orbit bright stars provide the best opportunities for accurate abundance measurements .
For this reason , we measured the transmission spectrum of the bright ( V \sim 10.2 ) , large ( 1.37 R _ { J } ) , sub-Saturn mass ( 0.19 M _ { J } ) exoplanet WASP-127b across the near-UV to near-infrared wavelength range ( 0.3–5 \mu m ) , using the Hubble and Spitzer Space Telescopes .
Our results show a feature-rich transmission spectrum , with absorption from Na , H _ { 2 } O , and CO _ { 2 } , as well as wavelength-dependent scattering from small-particle condensates , and a grey absorber which somewhat mutes the molecular absorption features .
We ran two types of atmospheric retrieval models : one enforcing chemical equilibrium , and the other which fit the abundances freely .
Our retrieved abundances at chemical equilibrium for Na , O and C are all super-solar , with abundances relative to solar values of 51 ^ { +30 } _ { -29 } , 23 ^ { +15 } _ { -9 } , and 33 ^ { +43 } _ { -15 } respectively .
Despite giving conflicting C/O ratios , both retrievals gave super-solar CO _ { 2 } volume mixing ratios , which adds to the likelihood that WASP-127b ’ s bulk metallicity is super-solar , since CO _ { 2 } abundance is highly sensitive to atmospheric metallicity .
In the future , spectroscopy with JWST will be able to constrain WASP-127b ’ s C/O ratio , and may reveal the formation history of this metal-enriched , highly observable exoplanet .