Billions of years ago, Mars was a much different place than it is today. During the same period when life was first emerging on Earth, Mars had a thicker atmosphere, warmer surface temperatures, and flowing water on its surface. Evidence of this warmer, wetter past is preserved on the planet’s surface today in the form of river channels, lakebeds, alluvial fans, and sedimentary deposits. When this period began, and how long it lasted, remains the subject of much debate for scientists.

Knowing how long this period lasted helps establish how big the window of opportunity was for life on Mars. But according to new NASA-funded research from the Sellers Exoplanet Environments Collaboration (SEEC), Mars may have been wetter longer than previously expected. According to recently published results in the Proceedings of the National Academy of Sciences, Mars may have had a northern ocean as recent as three billion years ago.

The international SEEC team included researchers from the University Paris-Saclay, the Institut Universitaire de France, the Centre National de la Recherche Scientifique (CNRS), the Center for Climate Systems Research (CCRS) at Columbia University, Uppsala University, the NASA Goddard Institute for Space Studies (GISS), and the NASA Goddard Space Flight Center.

This conceptual image reveals what the Kasei Valles region on Mars may have looked like three billion years ago. Credits: F. Schmidt/NASA/USGS/ESA/ DLR/FU Berlin (G. Neukum)

Based on data provided by multiple robotic missions (landers, rovers, and orbiters), it is widely believed that the late Noachian Period (ca. 4.1 to 3.5 billion years ago) was the only geological period where Mars was habitable. Based on the valley networks observed near the equator (features that form from erosion due to flowing water), there was significant rain near the equator during this period.

This period did not last, as Mars lost its global magnetic field, and its atmosphere was slowly stripped away by solar wind. Over the ensuing eons, Mars gradually transitioned to the very cold, desiccated, and almost airless environment that we see there today. Knowing how long this period of habitability lasted is key to the current search for evidence of past life on Mars. The longer the window, the more likely it is that fossilized evidence of life can be found on Mars today.

In their study, the SEEC collaboration extended the potentially habitable period on Mars by about 500 million years into the late Hesperian Period (ca. 3.7 to 3 billion years ago). As co-author Frédéric Schmidt, a researcher with the University Paris-Saclay, explained in a NASA press release:

“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. 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.”

This conceptual image reveals what the Kasei Valles region on Mars looks like today. Credits: F. Schmidt/NASA/USGS/ESA/ DLR/FU Berlin (G. Neukum)

The team used the ROCKE-3D Global Climate Model
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