The Planets: Mars

“Our simulation revealed that three billion years ago, the climate in much of the northern hemisphere of Mars was very similar to present-day Earth, with a stable ocean,” said Frédéric Schmidt of the University Paris-Saclay, France, co-lead author of a paper on the research published in the Proceedings of the National Academy of Sciences Jan. 17. “Our result contradicts theories claiming that such a northern ocean could not be stable. It also increases the time period for an Earth-like climate on Mars.”

The late Noachian period (from 4.1 billion to 3.5 billion years ago) is the period usually thought to be habitable on Mars, with significant rain near the equator, as demonstrated by the presence of valley networks – features formed by erosion from flowing water -- at this age.

However, this clement period was not to last, and as the eons passed Mars gradually transitioned to its present-day climate, with an atmosphere too cold and thin to support liquid water, a necessary ingredient for life, on the surface. Scientists want to know the duration of the habitable period; the longer it was, the more time there would have been for any potential Martian life to form. The new work extends the potentially habitable period on Mars by about 500 million years, into the late Hesperian age.

“Discerning the climate of Mars approximately three billion years ago is challenging because the Martian surface features do not seem to fully support either a warm and wet or cold and dry climate during that time,” said Michael Way, co-lead author of the paper at NASA’s Goddard Institute for Space Studies, New York. “A warm and wet climate would have produced extensive erosion from flowing water, but few valley networks have been observed from this age. A too-cold climate would have kept any northern ocean frozen most of the time. A moderate cold climate would have transferred the water from the ocean to the land in the form of snow and ice. But this would prevent tsunami formation, for which there is some evidence.” ...