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Mars’ raindrops can be one time bigger than the Earth

Billions of years ago, rain on Mars was difficult enough for the shape of the planet’s surface, carving channels in the red earth and the washing away of parts of impact craters, new research suggests.

Some of the Red Planet raindrops that in the past were probably even higher than we are used to here on Earth, according to the study.

The authors of the study — Robert Craddock of the Smithsonian Institution in Washington, D. C., and Ralph Lorenz of the Johns Hopkins University Applied Physics Laboratory in Laurel, Maryland — to the example of the precipitation of ancient Mars by taking into account how the atmosphere of the planet has changed over the eons. [ Photos: The Search for Water on Mars ]

Just after Mars formed about 4.5 billion years ago, it likely had a thick atmosphere with a pressure which is approximately four times that of the Earth, the current of air, the researchers determined. They have calculated that such high pressure would have resulted in small drops of rain on only 3 millimeters or so.

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But the pressure has dropped on Mars as the years went on, the change of the nature of the planet’s rain, the researchers said.

“Through the use of physical principles to understand the relationship between the atmosphere, a 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 previous mist-like drops,” Lorenz said in a statement .

At an atmospheric pressure equal to that of the Earth, for example, the Martian raindrop diameter probably maxed out at about 7.3 mm — nearly 1 mm larger than the current Earth falls, the researchers found.

“However, the rainfall from such a storm would only be about 70 percent as intense on Mars, mainly due to the lower Martian gravity and the resulting lower terminal velocities of the raindrops,” Craddock, and Lorenz wrote in the new study, which was just published online in the journal Icarus .

“There will always be some unknowns, of course, such as how high a storm cloud may have risen in the atmosphere , but we have efforts to apply the range of existing variables for precipitation on Earth,” Craddock said in the statement. “It is unlikely that the rainfall on Mars would be dramatically different than what’s described in our paper. Our findings provide new, more definitive, limitations about the history of water and climate on Mars.”

That history is moved. Data collected by NASA’s Mars orbit the MAVEN spacecraft suggests that by 3.7 billion years ago, the solar wind had stripped away most of the Red Planet’s air . Today, Mars is carbon dioxide-dominated atmosphere is just 1 percent as thick as that of the Earth.

As a result of this loss, Mars shifted from a relatively warm and wet world with rivers, lakes and perhaps even oceans — the cold and dry planet we know today.

Follow Mike Wall on Twitter @michaeldwall and Google+ . Follow us @Spacedotcom , Facebook or Google+ . Originally published on Space.com .

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