Mars' Ancient Climate: Icy Cold or Warm and Wet? New Models Reveal the Past

Scientists have learned a bit more about the ancient climate of Mars. Researchers have taken a look at two opposite climate scenarios for the Red Planet and have found that a cold an icy planet may better explain the water drainage and erosion features seen on the planet today.

For decades, scientists have debated what the climate history of Mars might have been and how the planet's early climate led to the many water-carved channels seen today. One idea was that 3 to 4 billion years ago, Mars was warm, wet, and Earth-like with a northern sea. These conditions may have supported life. Another idea, though, was that Mars was a frigid, icy planet where water was locked in ice most of the time and life would have had a harder time evolving.

In order to see which explanation fit the best, the researchers used a three-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. In one scenario, the researchers looked at Mars as a warm and wet planet with an average temperature of 50 degrees Fahrenheit. In the other scenario, the researchers looked at Mars as a cold an icy world with an average temperature of minus 54 degrees Fahrenheit.

So what did they find? The colder scenario would be far more likely. Because Mars only gets 43 percent of the solar energy of Earth and early Mars was lit by a younger sun, this means that it's very likely that early Mars was cold and icy. In addition, an extreme tilt of the Martian axis would have pointed the planet's poles at the sun and driven polar ice to the equator, where water drainage and erosion features are seen today. And under a thicker atmosphere, equatorial highland regions would get colder and northern lowland regions would get warmer.

"I'm still trying to keep an open mind about this," said Robin Wordsworth, one of the researchers, in a news release. "There is lots of work to be done but our results show that the cold/icy scenario matches the surface distribution of erosion features more closely. This strongly suggests that early Mars was generally cold, and water was supplied to the highland regions as snow, not as rain."

The findings are published in the Journal of Geophysical Research: Planets.

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