A new study conducted by Northwestern University, USA, is the first to include 3D chemistry to understand how a star’s radiation heats or cools a rocky planet’s atmosphere.
The research team is the first to combine 3D climate modelling with atmospheric chemistry in order to explore the habitability of planets around dwarf stars. Using this tool, astronomers were able to redefine the conditions that make a planet habitable by taking the star’s radiation and the planet’s rotation rate into account.
The team from Northwestern University collaborated with researchers from the University of Colorado Boulder, USA, NASA’s Virtual Planet Laboratory and the Massachusetts Institute of Technology. The collaboration discovered that only planets orbiting active stars, those that emit a lot of ultraviolet (UV) radiation, lose large amounts of water to vaporisation. Additionally, the team discovered that planets around inactive stars are more likely to maintain liquid water.
The researchers also found that planets that possess thin ozone layers, that otherwise have habitable surface temperatures, receive dangerous levels of UV radiation.
“For most of human history, the question of whether or not life exists elsewhere has belonged only within the philosophical realm,” said Northwestern’s Howard Chen, the study’s first author. “It’s only in recent years that we have had the modelling tools and observational technology to address this question.”
“Still, there are a lot of stars and planets out there, which means there are a lot of targets,” added Daniel Horton, senior author of the study. “Our study can help limit the number of places we have to point our telescopes.”
“3D photochemistry plays a huge role because it provides heating or cooling, which can affect the thermodynamics and perhaps the atmospheric composition of a planetary system,” Chen said. “These kinds of models have not really been used at all in the exoplanet literature studying rocky planets because they are so computationally expensive. Other photochemical models studying much larger planets, such as gas giants and hot Jupiters, already show that one cannot neglect chemistry when investigating climate.”
“It has also been difficult to adapt these models because they were originally designed for Earth-based conditions,” Horton said. “To modify the boundary conditions and still have the models run successfully has been challenging.”