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Scalding Rains, Flash Floods and Worse Plagued Ancient Mars
By Robert Roy Britt
Senior Science Writer
posted: 05:32 pm ET
05 December 2002
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Mars in the popular imagination is a planet that was once warm and wet, a place that might have fostered life. But new research shows how these imagined pleasant periods were brief, hellish, and punctuated by utter catastrophe. New and detailed computer modeling paints a picture of blankets of molten rock, scalding rain andcolossal floods more than 3 billion years ago that rapidly and permanentlyscarred vast regions of the surface following crushing impacts from comets or asteroids. The scenario doesn't bode too well for little green men.Mars experts think a period of heavy bombardment in the early solar system, when planets acted like gravitational brooms and swept up the majority of space rocks, could have provided Mars warmth and water, two key ingredients for life."Our scenario provides both of these but it is in overkill," said Teresa Segura, a doctoral candidate at the University of Colorado at Boulder. Roughly 25 space rocks between 60 and 150 miles in diameter (100-250 kilometers) gouged the Martian surface every 10-20 million years back then. An impact of this size would rock the planet, fueling quakes and volcanic activity. But that would not be the end of it. A typical impact, Segura said, would have generated enough water in the ensuing years to bury the entire planet under "tens of meters" of water, or more than the height of a two-story building.Scientists at NASA's Ames Research Center contributed to the study, which will be detailed in the Dec. 6issue of the journal Science.Splash!Segura and her colleagues looked into how networks of large valleys, seen on Mars today, might have been created, given that the planet's thin and cold atmosphere cannot retain liquid water. They modeled how an impact might have liberated tremendous amounts of ice that could have been delivered in the space rock or that had existed beneath the planet's surface. Water would have been thrust into the atmosphere as hot vapor, the model shows. Other studies have laid this scenario out before, but none have precisely tracked and quantified the water and its environmental effects.Enough water should have been liberated to carve the valley networks, the study concluded. Segura described for SPACE.com the details of a typical large impact, one roughly ten times bigger than the 6-mile-wide (10-kilometer) asteroid suspected of killing off the dinosaurs. Vaporized rock and ice from the incoming object and the impact site expands ballistically in a huge cloud, she said, filling the global atmosphere. "Eventually, the atmosphere cools enough to condense the rock portion of the 'cloud' and the rock vapor-melt precipitates out over the entire planet, creating a global rock melt layer meters to tens of meters thick," Segura said. A meter is roughly equal to three feet."This stuff is hot, hotter than lava on the Big Island of Hawaii," she said.Eventually, the atmosphere cools enough to condense the water. Heavy rains ensue . up to six feet of scalding rain every year . lasting for perhaps hundreds of years. Meanwhile, the hot rock layer melts ice in the soil of Mars. The resulting floods "may be responsible for the river valleys we see on the planet," she said. "The other interesting consequence of the impact is the hot rock debris layer takes a long time to cool. We find that globally, Mars will be above the freezing point of water -- all water will be in the liquid phase -- for years to millennia for the largest objects."The study, like others that suggest catastrophic flooding on Mars, would explain oddities in the Martian landscape: "We definitely see river valleys but not tributaries, indicating the rivers were not as mature as those on Earth," said Professor Owen Toon, Segura's academic adviser and a co-author of the study. Toon said large craters on Mars are about the same age as the river valleys, which sparked their interest in the study.No place like homeSuch an environment would not have been a great place to raise kids, even of the microscopic variety. Even a few thousand years of warmth is an eyeblink in the evolutionary sense.While some scientists have theorized that the wet periods on Mars fueled longer lasting, greenhouse-like climates that would have been kind to evolution, Segura and her team think otherwise. They envision a cold and dry planet, "an almost endless winter, broken by episodes of scalding rains followed by flash floods."However, Earth experienced thissame period of heavy bombardment early in its development, and life did get going here, Segura points out. In fact, many scientists imagine that comets played a key role in delivering the water that built Earth's oceans, setting the stage for life to begin.It is not clear, however, whetherlife on Earth began once and then survived the latter stages of thebombardment, or if life was forced to began more than once, or if it simplywaited until after the assault slowed down considerably, some 3.8billion years ago. Whatever, biologists generally believe that life did develop hardy strains that endured punishing periods. Even in relatively modern geologic times, over the past few hundred million years, extinction events have destroyed many or most species but left some to thrive."We found, from our simulations, that the first ten or so meters of soil will heat to deathly temperatures," Segura said. "Below that depth, it is possible that some life forms were able to survive, just as they did on Earth."Scientists do not know if Marsdoes or ever did support life. Living creatures or fossils might lurk justunder the surface. Finding the possible signs of life, many scientists believe, will require a human mission to the planet, which is not yet planned.Artist'sRenderings of Ancient MarsHow LifeMight have Formed in a Martian Impact Crater | | | |
