Posted: September 11, 2008
New computer simulations suggest that the massive valley networks that define the surface of Mars could have been carved out by recurrent flooding rather than a short-lived catastrophic event.
"Our results argue for liquid water being stable at the surface of
Although the presence of water on Mars has been widely debated for many decades, it is only in recent years that NASA has acquired the high-resolution topographic data needed to definitively prove that the massive valley networks, thought to have formed over 3.5 billion years ago, were the result of action from rain and runoff. The mechanism for flooding, however, is much debated, and some studies based on climate models have suggested that catastrophic events such as asteroid impacts could have created sudden warm, wet conditions on Mars, causing massive deluges lasting for periods of hundreds to thousands of years.
On the southern Highlands of Mars, ancient river valley networks carve the surface. Parana Valles dominates one such valley network and cuts across a region roughly the size of California (frame A). New computer models test different climate scenarios on surfaces constructed to mimic Mars over 4 billion years ago before the valleys formed (B). Models that recreate a climate similar to ones found on Earth's deserts, with intermittent floods and long dry spells, recreate the valley networks over time periods
But in the new study, which focuses on one particular area of Mars – the valley networks near the Parana Basin – researchers show that catastrophic flooding would result in features not reflected by the martian landscape.
"Our research finds that these catastrophic anomalies would be so humid and wet there would be breaching of the craters," says Barnhart. “As the craters overflowed, exit breaches would cut into the crater rim, a feature we rarely see on Mars and one that isn't present near Parana Basin. The precipitation needs to be seasonal or periodic, so that there are periods of evaporation and infiltration, otherwise the craters overflow."
In order to reach this conclusion the researchers used a landform evolution model and ran over 70 simulations to determine how the surface of Mars would evolve under different climate conditions. “If we ran simulations in which these high discharges were continuous, the valley networks would form no problem, but many if not all of the craters would fill and overflow,” Barnhart tells Astronomy Now. Therefore, the authors conclude, the valleys could not have formed continuously in one or a few deluge-style scenarios.
The authors also compared the timescales required to make similar valley conditions on the Earth with those seen on Mars, and find that for Earth’s arid regions where rainfall occurs just two percent of the year, valley formation takes at least 10,000 years. “This creates a surface that more closely resembles the actual surface of Mars,” says Barnhart.
The authors also comment that 10,000 years is a lower limit, and that valley formation could have taken a lot longer if the valley forming discharge events were much less frequent.
The authors hope that future climate models and spacecraft observations will help to resolve the issue of how exactly the valley networks came to be, but they do have an upper limit: most planetary scientists agree that valley network formation ceased around 3.7 to 3.9 billion years ago, meaning that the valleys had to form within a few 100 million years.
A paper describing the findings has been accepted for publication in the Journal of Geophysical Research - Planets.
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