Universe Today
Ever since the Mariner probes and Viking missions travelled to Mars, scientists have known that liquid water once flowed on the surface. This is indicated by specific features that form in the presence of water here on Earth, including flow channels, delta fans, hydrated minerals, and sedimentary rocks. In recent decades, the many missions that have studied Mars' atmosphere, surface, and climate have revealed that Mars was a warmer, wetter place during the Noachian period (ca. 4.1 to 3.7 billion years ago).
This has stimulated questions about whether life could have emerged on Mars and where its once-abundant water (and maybe even life) could be found today. A new study by geologists at the University of Colorado Boulder (CU Boulder) provides a potential glimpse of what Mars may have looked like billions of years ago. Their findings suggest Mars experienced heavy precipitation that likely fed valleys and channels that carved the features we still see there today.
The research was led by Amanda Steckel, a postdoctoral geological scientist at Caltech (formerly at CU Boulder), and a member of the Perseverance science team. She was joined by Gregory E. Tucker, a geoscience professor at CU Boulder and a member of the Cooperative Institute for Research in Environmental Sciences (CIRES); Matthew Rossi and Brian Hynek were also co-authors on the study, a research scientist with CIRES and the Earth Lab and a geosciences professor with the Laboratory for Atmospheric and Space Physics (LASP) at CU Boulde, respectively.
While most scientists agree that Mars once had flowing water on its surface, where it came from remains a mystery. While most maintain that a global ocean once covered the entire Northern Lowlands of Mars, while large bodies spotted the southern hemisphere, many scientists assert that Mars was always cold and dry. In this scenario, water existed mainly as ice caps and glaciers that occupied the Northern Lowlands, which experienced occasional melting for short periods.
This is largely based on the fact that roughly 4 billion years ago, the young Sun was only 75% as bright as it is today. As a result, Mars must have had a significant greenhouse effect to maintain temperatures warm enough to support liquid water. Hence, there is an ongoing debate between proponents of the "warm-and-wet" versus the "cold-and-dry" models. To address this, Steckel and her colleagues ran a computer simulation originally developed for Earth studies by Professor Tucker. As Steckel explained in a CU Boulder press release:
"You could pull up Google Earth images of places like Utah, zoom out, and you’d see the similarities to Mars. It’s very hard to make any kind of conclusive statement. But we see these valleys beginning at a large range of elevations. It’s hard to explain that with just ice."
The researchers used the software to model the evolution of the Martian landscape on synthetic terrain similar to Mars' equatorial region. They added water from precipitation to some of their models and melting ice caps to others, and then simulated how this would shape the landscape over tens to hundreds of thousands of years. The team then compared the two models to data obtained by NASA's Mars Global Surveyor (MGS) and Mars Odyssey spacecraft. The precipitation model was consistent with what we see around Mars' equator today.
These include the vast network of channels in the Martian highlands that open onto the low-lying areas in the Northern Lowlands. The rock deposits and delta fans found in these areas further indicate that vast quantities of water once flowed across the landscape. "You'd need meters deep of flowing water to deposit those kinds of boulders," said Hynek. "Once the erosion from flowing water stopped, Mars almost got frozen in time and probably still looks a lot like Earth did 3.5 billion years ago."
While these results are convincing, there are still unanswered questions about Mars' ancient climate. For example, scientists are still unsure how Mars could maintain temperatures warm enough to support precipitation and flowing water, given how the Sun's output was less than it is today. However, this study still provides scientists with a glimpse at what Mars experienced in the past and could also provide new perspectives into the geological history of Earth.
Further Reading: University of Colorado
