There is substantial evidence to suggest that Mars was once a wet and warm planet. Our orbiters have revealed intricate channel systems that were carved by rivers flowing across its surface. It is even possible that expansive oceans, larger than those on Earth, once covered a significant portion of Mars. However, something occurred that caused Mars to lose its atmosphere and for surface water to disappear.
As our understanding of Mars deepens, it is becoming apparent that the loss of water on Mars was not a single catastrophic event. Instead, there is mounting evidence to suggest that it was a gradual process. It is likely that Mars experienced recurring episodes of surface water that persisted intermittently over an extended period of time. If this is indeed the case, it could have significant implications for the potential existence of life on Mars.
Recent findings presented in Earth and Planetary Science Letters are strengthening the notion that the process of Mars losing its water may have been a lengthy one. The research letter is titled “New Maximum Constraints on the Era of Martian Valley Network Formation.” The author is Alexander Morgan, a research scientist at the Planetary Science Institute who studies geomorphology.
“Mars today is a global desert, but its surface preserves extensive evidence of past flowing water, including what appear to be river valleys. The timescale over which these valleys formed has big implications for early Mars habitability, as long eras with stable liquid water would be more conducive to life,” says Morgan
The extensive evidence of ancient rivers on Mars thanks to the Perseverance Rover. The location explored is known as Jezero Crater, a place where an impact crater from the past can be found. In bygone eras, this crater experienced a significant influx of water, resulting in the formation of an extensive sedimentary basin. Detailed images taken from orbit depict the presence of ancient river channels that flowed into this immense crater.
The Perseverance rover's landing site on Mars reveals a fascinating combination of impact craters and rivers seamlessly intertwining with each other. This discovery forms the foundation of Morgan's research. By determining the age of craters located near river channels, he was able to establish a timeframe for when these rivers were active in shaping the channels.
“In this study, I used craters that predate and postdate valley systems to place maximum bounds of hundreds of millions of years on the era over which these systems formed. Previous work had only determined minimum timescales, so these new results provide an upper bound on the timescale over which Martian valleys were active. Given what we know about erosion rates on early Mars, longer timescales imply that conditions permitting rivers were highly intermittent, with long arid periods interspersed with brief episodes of fluvial activity.” said Morgan
Over three billion years ago, the river valleys on Mars were formed, providing the most compelling evidence of the planet's past existence of surface water. Extensive research indicates that it takes thousands of years for flowing water to carve valleys into the Martian surface. However, the number of flow events and the total time it took for these valleys to form remained a mystery, until now.
In recent years, our knowledge of Mars has significantly expanded and will continue to do so. A revolution is taking place in our understanding of its climate history. Previously, there were two opposing theories regarding Mars' ancient past. One proposed that the planet was warm, wet, and potentially able to support life. The other suggested that Mars was a freezing cold planet covered in ice sheets.
Throughout our extensive study of Earth, we have come to understand that its climate has experienced significant fluctuations over its long history. There were periods when the Earth was engulfed in vast glaciers that reached several kilometers in thickness. Conversely, there were also times when these glaciers receded to their mountain strongholds. It is only logical to wonder if other planets have undergone similarly diverse and varied histories.
Just like Earth, early Mars was a complex planet, and it is highly likely that the conditions necessary for surface water varied considerably. Earth itself has witnessed massive climatic transformations throughout its existence. For instance, around 20,000 years ago, what is now known as Chicago was buried under half a mile of ice. It can be reasonably assumed that the surface conditions on early Mars also experienced fluctuations, allowing for the formation and disappearance of rivers.
Throughout our extensive study of Earth, we have come to understand that its climate has experienced significant fluctuations over its long history. There were periods when the Earth was engulfed in vast glaciers that reached several kilometers in thickness. Conversely, there were also times when these glaciers receded to their mountain strongholds. It is only logical to wonder if other planets have undergone similarly diverse and varied histories.
Just like Earth, early Mars was a complex planet, and it is highly likely that the conditions necessary for surface water varied considerably. Earth itself has witnessed massive climatic transformations throughout its existence. For instance, around 20,000 years ago, what is now known as Chicago was buried under half a mile of ice. It can be reasonably assumed that the surface conditions on early Mars also experienced fluctuations, allowing for the formation and disappearance of rivers.
“Over short timescales, river flow is controlled by rainfall or upstream snow melt. Over longer timescales, Earth’s rivers are affected by climatic changes. For example, 20,000 years ago, there were large lakes and larger rivers across what is now Nevada. Martian rivers would have operated in a similar way, with short-term variability due to storms or snowmelt, and longer-term variability due to changes in the planet’s spin and orbit around the Sun.” stated Morgan
The planet Mars may have experienced periods of intense volcanic activity that caused the warming of the planet, resulting in the melting of ice sheets and the formation of distinct channels on its surface. This is evident in the Tharsis Montes region, where three enormous shield volcanoes are located, surpassing the size of Earth's volcanoes. Additionally, the largest volcano in the entire Solar System, Olympus Mons, is situated just northwest of Tharsis Montes.
The mysteries surrounding Mars remain largely unanswered. Is Mars simply a typical example of planets that were once marginally habitable but eventually became uninhabitable? Alternatively, could it be an exceptional case of a planet that managed to retain its water through various climatic changes? Did simple forms of life emerge on Mars before becoming extinct, and is this a common occurrence in the universe? Or is the presence of surface water on any planet, for any significant period of time, an extremely rare phenomenon?
At present, we lack definitive answers to these profound questions. Planets are complex entities, vast in size, with long lifespans, and continuously evolving. Unraveling the events that transpired billions of years ago on a planet is an immensely challenging endeavor.