Using forward models for representative exoplanet atmospheres and a radiometric instrument model , we have generated synthetic observational data to explore how well the major C- and O-bearing chemical species ( CO , CO _ { 2 } , CH _ { 4 } , and H _ { 2 } O ) , important for determining atmospheric opacity and radiation balance , can be constrained by transit measurements as a function of spectral wavelength coverage .
This work features simulations for a notional transit spectroscopy mission and compares two cases for instrument spectral coverage ( wavelength coverage from 0.5 - 2.5 \mu m and 0.5 - 5 \mu m ) .
The simulation is conducted on a grid with a range of stellar magnitudes and incorporates a full retrieval of atmospheric model parameters .
We consider a range of planets from sub-Neptunes to hot Jupiters and include both low and high mean molecular weight atmospheres .
We find that including the 2.5–5 \mu m wavelength range provides a significant improvement in the degree of constraint on the retrieved molecular abundances : up to \sim 3 orders of magnitude for a low mean molecular weight atmosphere ( \mu = 2.3 ) and up to a factor of \sim 6 for a high mean molecular weight atmosphere ( \mu = 28 ) .
These decreased uncertainties imply that broad spectral coverage between the visible and the mid-infrared is an important tool for understanding the chemistry and composition of exoplanet atmospheres .
This analysis suggests that the JWST/NIRSpec 0.6 - 5 \mu m prism spectroscopy mode , or similar wavelength coverage with possible future missions , will be an important resource for exoplanet atmospheric characterization .