[LINK] "New study favors cold, icy early Mars"

[rfmcdonald]

The Dragon's Tales linked to a press release suggesting that Mars in its youth was never a warmer and wetter world analogous to Earth, that it has always been chill.

For decades, researchers have debated the climate history of Mars and how the planet's early climate led to the many water-carved channels seen today. The idea that 3 to 4 billion years ago Mars was once warm, wet and Earth-like with a northern sea -- conditions that could have led to life -- is generally more popular than that of a frigid, icy planet where water is locked in ice most of the time and life would be hard put to evolve.

To see which early Mars better explains the modern features of the planet, researcher Robin Wordsworth of the Harvard Paulson School of Engineering and Applied Sciences and his colleagues used a 3-dimensional atmospheric circulation model to compare a water cycle on Mars under different scenarios 3 to 4 billion years ago, during what's called the late Noachian and early Hesperian periods. One scenario looked at Mars as a warm and wet planet with an average global temperature of 10 degrees Celsius (50 degrees Fahrenheit) and the other as a cold and icy world with an average global temperature of minus 48 degrees Celsius (minus 54 degrees Fahrenheit).

The study's authors found that the cold scenario was more likely to have occurred than the warm scenario, based on what is known about the history of the Sun and the tilt of Mars's axis 3 to 4 billion years ago. The cold model also did a better job explaining the water erosion features that have been left behind on the Martian surface, and which have puzzled and intrigued scientists since they were first discovered by the Viking orbiters in the 1970s.

[. . .]

The colder scenario was more straightforward to model, Wordsworth explained, because Mars only gets 43 percent of the solar energy of Earth, and early Mars was lit by a younger Sun believed to have been 25 percent dimmer than it is today. That makes it very likely early Mars was cold and icy, he said.