Primary atmosphere

A primary atmosphere is an atmosphere of a planet that forms by accretion of gaseous matter from the accretion disc of the planet's sun. Planets such as Jupiter and Saturn have primary atmospheres. Primary atmospheres are very thick compared to secondary atmospheres like the one found on Earth. The primary atmosphere was lost on the terrestrial planets due to a combination of surface temperature, mass of the atoms and escape velocity of the planet.

Detection of CO2 in Exoplanetary Atmospheres and Implications for Primary Atmospheres

Recent observations by the James Webb Space Telescope (JWST) have provided groundbreaking insights into the atmospheric composition of exoplanets, which are vital for understanding both primary and secondary atmospheres. A notable example is the detection of carbon dioxide (CO2) in the atmosphere of the exoplanet WASP-39b. This detection, achieved through transmission spectroscopy in the 3.0-5.5 micrometre wavelength range, has revealed a significant CO2 absorption feature at 4.3 micrometres, with a 26-sigma significance. These findings are critical as CO2 is a key indicator of metal enrichment in planetary atmospheres, influence the formation process of primary atmospheres of gas giants.

The JWST data suggests that the atmospheric composition of WASP-39b includes not only CO2 but also water, carbon monoxide, and hydrogen sulfide, with moderate cloud opacity and little methane. This composition aligns with one-dimensional models assuming a ten-times solar metallicity and radiative-convective-thermochemical equilibrium. The presence of these gases in the atmospheres of hot gas giants like WASP-39b provides insights into the processes that may have shaped the primary atmospheres of similar massive planets in our solar system.