A new animation by NASA scientists illustrates what Mars ? the fourth planet from the Sun andthe second smallest planet in the Solar System ? may have looked like billions of years ago.
Today, Mars is a cold, desert world. Liquid water cannot exist pervasively on its surface due to thelow atmospheric pressure and surface temperature, although there is evidence for spurts of liquidflow that perhaps consist of a briny solution with reduced freezing temperature. Water undercurrent conditions can be ice or sublimate directly into vapor without staying in a liquid phase.
Around 4 billions of years ago when the planet was young, it appears to have had a thickatmosphere that was warm enough to support oceans of liquid water ? a critical ingredient for life.
The animation shows how the surface of the Red Planet might have appeared during this ancientclement period, beginning with a flyover of a lake.
“There are characteristic dendritic structured channels that, like on Earth, are consistent withsurface erosion by water flows. The interiors of some impact craters have basins suggesting craterlakes, with many showing connecting channels consistent with water flows into and out of thecrater,” explained Dr Joseph Grebowsky from NASA’s Goddard Space Flight Center in Greenbelt,who is the project scientist for NASA’s Mars Atmosphere and Volatile Evolution (MAVEN) mission.
“Small impact craters have been removed with time and larger craters show signs of erosion bywater before 3.7 billion years ago. And sedimentary layering is seen on valley walls. Minerals arepresent on the surface that can only be produced in the presence of liquid water.”
Estimates of the amount of water needed to explain these features have been made that equatedto possibly as much as a planet-wide layer 1,640 feet deep or more. If liquid surface water existedin the past, then Mars’ atmosphere had to have had a different climate that was warmer and apressure near or greater than the current terrestrial atmospheric pressure at the surface.
In the animation, rapidly moving clouds are employed to suggest the passage of time, and theshift from a warm and wet to a cold and dry climate is shown as the video progresses.
The lakes dry up and freeze over, while the atmosphere gradually transitions from Earthlike blueskies to the dusty pink and tan hues seen on Mars today.
It’s unknown if the habitable climate lasted long enough for life to emerge on Mars.
“The only direct evidence for life early in the history of a planet’s evolution is that on Earth,” DrGrebowsky said.
“The earliest evidence for terrestrial life is the organic chemical structure of a rock found on thesurface in Greenland. The surface was thought to be from an ancient sea floor sediment. The ageof the rock was estimated to be 3.8 billion years, 700 million years from the Earth’s creation. Nofossil evidence of life has yet been found from this period. The oldest claimed micro-fossils date to3.5 billion years ago. The existence of a potential life-nurturing climate on Mars ended near thesetimes. A comparison between the two planet’s life histories must be done with caution, due to thedifferent chemical compositions of the surfaces and different volcanic and meteoroid impacthistories. Also, the histories of life on either planet may not have been continuous. Catastrophicevents could have killed off all life at one time only to have it start anew.”
The animation ends with an illustration of NASA’s MAVEN mission in orbit around present-dayMars.
MAVEN will investigate how Mars lost its atmosphere. Scheduled to be launched in November, itwill arrive at Mars in September 2014.(ChinaDaily)
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NASA"火星大气和挥发性演化"(MAVEN)探测器项目科学家约瑟夫?格雷布斯基说：“火星表面有分布着许多树枝状的水道，就像地球上一样，这是水流冲刷的结果。”
而如果火星表面过去存在液态水，那么火星的大气层必须能营造更温暖的气候环境，还需要有一个与目前地球表面大气压相当或者更大的气压。
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目前尚不清楚火星上的宜居气候有多长，能否孕育生命。
格雷布斯基说：“在星球演变历史早期，有直接证据证明生命存在的星球只有地球。”
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