Icy Mars lakes warmed by methane


The release of methane trapped in Martian subsurface reservoirs following planetary obliquity shifts may have contributed to episodic climate warming between 3.6 and 3 billion years ago, explaining for ancient ice-covered lakes.

Decades of spacecraft investigations have confirmed that Mars preserves the geological record of an active and watery past. During the first billion years of the planet's history, known as the Noachian period, Mars probably had a denser atmosphere than today. Although the climate was relatively cold compared to Earth, there is evidence that liquid water flowed in streams and rivers, formed alluvial fans and deltas, and ponded in big lakes and possibly seas. The next 600 million years of Martian history -the Hesperian period- marked the transition from that early cold and wet Mars to a cold and icy planet via substantial atmospheric loss and decline in planetary heat flow. The last three billion years on Mars, the Amazonian period, have been dominated by extreme cold and dryness. Although liquid water was scarce during the Hesperian, Kite et al. argue in Nature Geoscience that episodic recurrences of cold and wet conditions triggered by bursts of methane stored in the subsurface may have sustained river flow and ice-covered lakes for durations of up to one million years.

The mineralogy and geomorphology of the Martian surface suggest largely cold and icy conditions during the Hesperian, when lakes would have been totally sealed by ice, and therefore isolate from their surrounding environment. However, rare episodes of runoff are recorded by deltas and alluvial fans in certain basins, suggesting occasional warming permitted exterior water to reach the ice-covered lakes.

Kite et al. suggest a warming mechanism for Hesperian climates that triggered by transitions in the planet's mean obliquity. Such transitions cause latitudinal changes in temperature and thus migration of ground and surface ice. The authors propose that chaotic excursions to high planetary obliquity act to episodically destabilize methane clathrates that are normally trapped beneath ice. The reduced pressure triggers the release of methane - a potent greenhouse gas.

Article published by Alberto G. Fairén in Nature Geoscience.

Image: Artist's impression of an ice-covered lake on ancient Mars. © STOCKTREK IMAGES, INC./ALAMY STOCK PHOTO


Fuente: UCC-CAB

Fecha: 2018-01-18


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