Many thought that if Mars had a stronger greenhouse effect, it might be more hospitable to life. It’s not a crazy idea. Mars has lots of carbon dioxide—much of it frozen. In the past, the CO2 as gas could have been in the atmosphere. And previous studies suggested that a denser CO2 atmosphere could have produced a warm and wet Martian climate.
But a new study throws cold water on that temperate Mars. Researchers ran global, 3D climate simulations for a variety of plausible Martian atmospheres. And even with a much thicker CO2 atmosphere, the greenhouse effect could not have warmed Mars above freezing. The study is in the journal Icarus. [Francois Forget et al., 3-D modelling of the early Martian climate under a denser CO2 atmosphere: Temperatures and CO2 ice clouds]
Mars has dry canyons and riverbeds, so water must have flowed at some point. But those flows may have been short-lived melting episodes triggered by volcanism or asteroid impacts. Because the idea of a balmy ancient Mars just got iced.
—John Matson
