硫是火星之谜的答案？

billkof

新研究提出，火星的大气也许曾经富含二氧化硫，这也许能解释该行星古老海洋的一个存在已久的迷。在早期火星的表面有液态水的证据意味着该行星气温曾经相对地暖。研究人员曾提出该行星早期被二氧化碳大气环绕，向地球上一样，二氧化碳大气能使火星有较暖的温度。但是火星表面没有石灰岩和其他碳酸盐石一直是个迷，这类岩石在地球上到处可见，它们通常在浅海中沉淀出来。Itay Halevy和同事现在提出，如果早期火星具有高浓度的来自火山爆法的二氧化硫和氢化硫，就能解释这个表面的矛盾。与二氧化碳类似，二氧化硫是一种高效的温室气体。但是二氧化硫增加海洋酸性阻止了碳酸盐矿物质的形成，从而解释了火星上为什么没有这类岩石。这样的机制可能在地球上也存在过，这也许能解释为什么地球上没有来自大约40亿到25亿年前的太古宙的碳酸盐岩石。
Reports
A Sulfur Dioxide Climate Feedback on Early Mars
Itay Halevy,1* Maria T. Zuber,2 Daniel P. Schrag1
Ancient Mars had liquid water on its surface and a CO2-rich atmosphere. Despite the implication that massive carbonate deposits should have formed, these have not been detected. On the basis of fundamental chemical and physical principles, we propose that climatic conditions enabling the existence of liquid water were maintained by appreciable atmospheric concentrations of volcanically degassed SO2 and H2S. The geochemistry resulting from equilibration of this atmosphere with the hydrological cycle is shown to inhibit the formation of carbonates. We propose an early martian climate feedback involving SO2, much like that maintained by CO2 on Earth.

1 Department of Earth and Planetary Sciences, Harvard University, Cambridge, MA 02138, USA.
2 Department of Earth, Atmospheric, and Planetary Sciences, Massachusetts Institute of Technology, Cambridge, MA 02139, USA.


* To whom correspondence should be addressed. E-mail: ihalevy@fas.harvard.edu