Image enhancement using a computer algorithm that highlights features with the properties of stream and river valleys shows strong evidence that Mars once had a great northern ocean and flowing streams on a great southern continent.The new research highlights the rivers and streams that flowed into the great northern ocean.
By FishOutofWater
Scientific investigations discovered a deformed ancient shoreline in 2007, indicating that Mars probably once had a large ocean.
Since 1991, planetary scientists have floated the idea that Mars once harbored vast oceans that covered roughly one-third of the planet. Two long shore-like lips of rock in the planet's northern hemisphere were thought to be the best evidence, but experts argued that they were too "hilly" to describe the smooth edges of ancient oceans.
The view just changed dramatically with a surprisingly simple breakthrough.
The once-flat shorelines were disfigured by a massive toppling over of the planet, scientists announced today (ed. in 2007). The warping of the Martian rock has hidden clear evidence of the oceans, which in any case have been gone for at least 2 billion years.
The research reported this week shows classic dendritic stream structures on Mars, like streams formed by water on earth. Original source, JGR Planets (subscription)
By FishOutofWater
Mars once had a temperate climate and flowing water. From the JGR research article (my bold in quoted text):
Recent advances in machine extraction of geomorphic features from topographic data [Molloy and Stepinski, 2007] make it feasible to acquire the VN map automatically - by computer parsing of the MEGDR. In this paper we use such automated approach to construct a planet-wide map of VN that would reveal more accurately the global pattern of dissection on Mars. The resultant map shows much more dense dissection than was depicted by [Carr and Chuang, 1997]. This result adds to the growing body of evidence that points toward precipitation-fed runoff erosion as an ultimate origin of VN, and thus toward the warm and wet climate on early Mars.
By FishOutofWater
The hemispheric separation of the great southern continent from the northern ocean kept moisture from reaching the interior of the southern continent. Most of the southern continent was very dry. Sufficient water to cause stream and river erosion was found primarily in the equatorial region of the southern continent. (My bold in quote of source article.)
The full account of implications the global pattern of dissection has on the origin of VN is beyond the scope of this paper. However, we offer a preliminary discussion of a particular scenario that may, conceivably, explain the major features of this pattern. This scenario is based on an exploratory discussion of climatic controlling factors on ancient Mars [Richardson and Soto, 2008]. We focus on explaining why the pattern of dissection on Mars is different from the terrestrial pattern, even assuming a best case scenario of an early Mars that was warm enough to support liquid water on its surface. The fundamental reason is the existence of the topographic dichotomy on Mars. Given the particular global topography of Mars, the water will accumulate in the topographic lows of the northern plains to form an "ocean." The confinement of a major water reservoir to northern plains restricts the transfer of water vapor to equatorial regions and the southern hemisphere where the VN are found. Global atmospheric circulation will carry moisture from northern midlatitudes southward resulting in precipitation when the air mass rises orographically upon encountering the dichotomy boundary. In fact, some of the heavily dissected regions are found where the topographic dichotomy is the most pronounced (see Figure 6). The supply of moisture to the regions located farther from the ocean would be limited. Diffusive atmospheric motions will deliver occasional storms to these regions, but in quantities much smaller than could be expected from the global inventory of water. Thus, in this scenario the equatorial and southern regions of Mars would experience an arid, "continental" climate not because of the lack of liquid water on the surface of the planet, but because of the physical separation of the water reservoir and the landmass. Such a scenario explains the relatively low dissection density and the existence of the southern limit to the presence of valley networks. The southernmost regions, located farthest from the water reservoir would get no rainfall and would develop no valleys. It also offers an explanation to shallowing of VN from (roughly) the location of topographic dichotomy, where largest rainfall rates result in more dissection, southward, where smaller rainfall rates result in less dissection. This hypothesis requires further scrutiny; in particular, it needs to be investigated whether potential existence of large "lakes" in the Hellas and Argyre basins would alter our reasoning. It is unclear how to explain the patchy character of dissection within a framework of this scenario.
Mars was once a planet fairly hospitable to life as we know it on earth. Now, it's ocean is gone and its atmosphere is much too thin for life as we know it. There is strong evidence that Venus was once more hospitable to life but went through a run away greenhouse catastrophe. However, on earth, living organisms have modified the atmosphere, maintaining atmospheric conditions that support evolving life. Planetary science shows that the stability of oceans and atmospheres cannot be assumed. Our neighbor planets have suffered from catastrophic planetary events.
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