The first planetary atmospheres may have been rich in water
To date, more than 4,000 exoplanets have been confirmed, with thousands more possible exoplanet detections. The physical properties and chemical compositions of these planets are important in understanding how planets form and whether they can support life. For example, the composition of an exoplanet’s atmosphere, which can be studied spectroscopically as the exoplanet passes in front of its host star, can provide information about the chemical makeup of the planet, as well as the processes on its surface. .
Thermodynamic models have been developed to explain the formation and evolution of planetary atmospheres. However, the experimental data available to constrain these models are limited. To understand how primary planetary atmospheres form during the formation of planets and how their compositions correlate with bulk planetary compositions, Maggie Thompson of the University of California at Santa Cruz and her colleagues performed degassing experiments on primitive meteorites. The research team selected three carbonaceous chondrites: Murchison, Jbilet Winselwan and Aguas Zarcas. A sample of each of these meteorites was heated to 1200°C, then the abundances of ten main gas species were measured by mass spectrometer when they were released from the rocks. For all three samples, water was the most abundant degassing species (66%), followed by carbon monoxide (18%) and carbon dioxide (15%). Small amounts (1% or less) of molecular hydrogen and hydrogen sulfide have also been observed. These experiments suggest that if terrestrial planets formed from carbonaceous chondrite-like materials, their primary atmospheres (if conserved) would be rich in water. The planetary atmospheres around the rocky planets of our solar system exhibit various chemical compositions, not all of which are rich in water. This suggests that they lost the original atmospheres that formed during the degassing of their interiors, and subsequently acquired secondary atmospheres through various processes. READ MORE