Valley networks on Mars showing evidence of surface runoff caused by rainfall. Image Credit: NASA/JPL-Caltech
Changes in Mars’s atmosphere over time made it rain harder and harder on the Red Planet, reshaping its surface and carving out river-like channels, according to a new study.
The effects are thought to have been similar to those caused by rainfall on Earth.
Researchers from the Smithsonian Institution and the Johns Hopkins University Applied Physics Laboratory were able to show that there was rainfall on Mars in the past, and analysed how the planet's atmosphere has changed since its formation 4.5 billion years ago.
Back then, it had a more substantial atmosphere creating a higher atmospheric pressure.
This would have meant very small water droplets creating something like fog rather than rain.
But, as the atmospheric pressure decreased over millions of years, the raindrops would have increased in size and the rain would have been substantial enough to alter the Martian surface.
Early on, the atmospheric pressure on the planet would have been about 4 bars, compared with Earth’s current 1 bar.
Raindrops would have been about 3mm across. As the pressure fell to 1.5 bars, it could have created raindrops about 7.3mm across.
“By using basic physical principles to understand the relationship between the atmosphere, raindrop size and rainfall intensity, we have shown that Mars would have seen some pretty big raindrops that would have been able to make more drastic changes to the surface than the earlier fog-like droplets,” says Dr. Lorenz of Johns Hopkins.
“There will always be some unknowns, of course, such as how high a storm cloud may have risen into the Martian atmosphere, but we made efforts to apply the range of published variables for rainfall on Earth,” says Dr. Craddock of the Smithsonian Institution.
“It’s unlikely that rainfall on early Mars would have been dramatically different than what's described in our paper.
Our findings provide new, more definitive constraints about the history of water and the climate on Mars.”