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古代火星上有冰川流动,但速度很慢

Glaciers flowed on ancient Mars, but slowly

The weight and grinding movement of glaciers has carved distinctive valleys and fjords into Earth’s surface. Because Mars lacks similar landscapes, researchers believed ancient ice masses on the Red Planet must have been frozen firmly to the ground. New research suggests they were not stuck in place, but just moved very slowly.

冰川的重量和研磨运动在地球表面雕刻出独特的山谷和峡湾。由于火星缺乏类似的地貌,研究人员认为,这颗红色星球上的古代冰块一定是牢牢地冻结在地面上的。新的研究表明,它们并没有固定在原地,只是移动得非常缓慢。

Motion is part of the definition of a glacier. On Earth, meltwater gathers below glaciers and ice sheets, lubricating the downhill slide of these rivers of ice. The new study modeled how Mars’ low gravity would affect the feedback between how fast an ice sheet slides and how water drains below the ice, finding under-ice channels would be likely to form and persist. Fast water drainage would increase friction at the interface of rock and ice.

移动是冰川定义的一部分。在地球上,冰川和冰原下的融水聚集在一起,润滑着这些冰川的下坡。这项新研究模拟了火星的低重力如何影响冰盖滑动速度和冰下水如何流失之间的反馈,发现冰下通道可能会形成并持续存在。快速排水会增加岩石和冰的接触面摩擦。

This means ice sheets on Mars likely moved, and eroded the ground under them, at exceedingly slow rates, even when water accumulated under the ice, the authors said. The new study was published in Geophysical Research Letters.

作者说,这意味着火星上的冰盖可能会移动,并以极慢的速度侵蚀它们下面的地面,即使当水在冰下积累时也是如此。这项新研究发表在《地球物理研究快报》上。

“Ice is incredibly non-linear. The feedbacks relating glacial motion, glacial drainage and glacial erosion would result in fundamentally different landscapes related to the presence of water under former ice sheets on Earth and Mars,” said Anna Grau Galofre, a planetary scientist at Laboratoire de Planétologie et Géosciences (LPG/ CNRS/ Nantes Université/ Le Mans Université/ Universtié d’Angers) and the lead author of the new study, conducted while she was a postdoc at Arizona State University.

“冰是不可思议的非线性。有关冰川运动、冰川排水和冰川侵蚀的反馈将导致与地球和火星前冰盖下是否存在水有关的根本性不同的景观,”安娜·格劳·加洛弗雷说。她是Planétologie和Géosciences实验室(LPG/ CNRS/南特Université/勒芒Université/ Universtié d’angers)的行星科学家,也是这项新研究的主要作者,她在亚利桑那州立大学做博士后时进行了这项研究。

Although Mars does not have the obvious U-shaped valleys that mark Earth’s glacial landscapes, Grau Galofre said, researchers have found other geologic traces suggesting glacier-like ice masses in Mars’ past, including gravel ridges called eskers and potential subglacial channels.

格劳·加洛弗雷说,尽管火星上没有明显的U形山谷,这是地球冰川地貌的标志,但研究人员已经发现了其他地质痕迹,表明火星过去存在过类似冰川的冰块,包括被称为eskers的砾石山脊和潜在的冰下通道。

“Whereas on Earth you would get drumlins, lineations, scouring marks and moraines, on Mars you would tend to get channels and esker ridges under an ice sheet of exactly the same characteristics,” Grau Galofre said.

格劳·加洛弗雷说:“在地球上,你会看到冰丘、线纹、冲刷痕迹和冰碛,而在火星上,你往往会在具有完全相同特征的冰盖下看到通道和埃斯克脊。”

Grau Galofre and her co-authors modeled the dynamics of two equivalent ice sheets on Earth and Mars with the same thickness, temperature and subglacial water availability. They adapted the existing physical framework that describes the drainage of water accumulated under Earth’s ice sheets, coupled with ice motion dynamics, to model Martian conditions and learn whether the subglacial drainage would evolve toward efficient or inefficient drainage configurations, and what effect this configuration would have on glacial sliding velocity and erosion.

格劳·加洛弗尔和她的合著者模拟了地球和火星上两个相同厚度、温度和冰下水可用性的冰原的动力学。他们改编了现有的物理框架,该框架描述了在地球冰盖下积累的水的排水,结合冰的运动动力学,以模拟火星的条件,并了解冰下排水是会朝着高效还是低效的排水配置演变,以及这种配置会对冰川滑动速度和侵蚀产生什么影响。

“Going from an early Mars with presence of surface liquid water, extensive ice sheets and volcanism into the global cryosphere that Mars currently is, the interaction between ice masses and basal water must have occurred at some point,” Grau Galofre said. “It is just very hard to believe that throughout 4 billion years of planetary history, Mars never developed the conditions to grow ice sheets with presence of subglacial water, since it is a planet with extensive water inventory, large topographic variations, presence of both liquid and frozen water, volcanism, [and is] situated further from the Sun than Earth.”

格劳·加洛弗尔说:“从存在表面液态水、广泛的冰盖和火山活动的早期火星到火星目前的全球冰冻圈,冰块和基底水之间的相互作用肯定在某个时刻发生过。”“很难相信,在40亿年的行星历史中,火星从未发展出存在冰下水的冰盖的条件,因为它是一个有大量水储量的行星,地形变化很大,存在液态和冰冻水,火山活动,[而且]比地球距离太阳更远。”

Read more at Phys.org

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