Wednesday, 10 August 2011

Repeated claims of discovery of Water on Mars

Yet another claim to discover water on Mars came out this month (August) – why jump to give it greater weight than previous evidence (Marc Kaufman)?

It's long accepted that channels and plains on Mars were sculpted by water early in the planet's history. Michael Carr described episodic flooding of underground water after initial oceans and seas had disappeared. The polar caps show that water moves to and from the polar caps, depending on changing orbital obliquity over millions of years (0.1 to several Myr). The first spacecraft (Viking) found diurnal frosting, indicating day-night movements of water.

NASA asked in 2001 does Water Exist on Present-day Mars?  Then scientific consensus held that liquid water cannot exist on the surface of Mars, the NASA story said. They counterposed Gil Levin's positive arguments for liquid water “in limited amounts and for limited times” with Chris McKay saying experiments show a layer of liquid could only be very short-lived.
Mars Express 2005 showed activity in modern times, with evidence of glaciers as recent as 20-30kyr ago, and sea-like horizontal terrain on Elysium Plantia formed by a sudden flood some 5 Myr ago (from few impact craters) leaving ice covered with a dirt/sand crust.
The Mars Orbiter's hi-res camera in 2008 showed a landform of dunes frosting and thawing  - as water sublimates, it leaves a dirty darker surface that being warmer in sunlight accelerates the thawing and erosion of the sand dunes. A similar feedback operates at Mars's north polar cliffs.

In Feb. 2009 we were told First liquid water may have been spotted on Mars, as drops on the legs of the Phoenix lander. This was followed in 2010 Liquid Water Found on Mars, whose author Richard A. Kerr reported Phoenix as showing liquid water has lately flowed on the frigid planet. The water may be liquid every martian spring or summer. Late in 2009, dark, finger-like features from a crater wall were interpreted as periodic flow.

Further HiRISE pictures of the features which appear and extend down some Martian slopes during the warmest months of the Mars year, show they fade in winter, then recur the next spring. Yet seasonal changes in colour can result not from flow but from diffusing water in the surface soil. Water in the pores is more stable against evaporation into the dry air and capilliary action can spread it as long as it stays mobile – which depends on temperature and salt or organic content (even live fungi or algae). Do the narrow features correspond to veins of salt – not to flowing water but damp enough to support pigmented photosynthesising organisms?

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