Wet, warm Mars Options

[ngunn]

Another one to chew over:
http://www.sciencedaily.com/releases/2008/...80625093242.htm

[dburt]

Another one to chew over:
http://www.sciencedaily.com/releases/2008/...80625093242.htm

Thanks. Haven't read more than that news story, but they seem to be comparing the Atacama Desert with Mars, and inferring that preferential chloride leaching from the surface indicates occasional rain or mist, based on the different relative solubilities of chlorides and sulfates. IMHO, possibly the wrong conclusion for the wrong planet - the old problem of using terrestrial processes as analogs for martian processes, rather than depending on basic physics and chemistry. I've been caught there myself e.g., as regards my recent informal discussion with Nick H. over how to make solid ground ice at the Phoenix site (my suggestion involving liquids was okay for solid salts, but probably not for solid ice, because it neglected the relatively high vapor pressure of ice). In other words, my suggestion explained how ice forms on relatively mild Antarctica, but probably not on much colder polar Mars. Nick was kind enough to set me straight, but also was kind enough NOT to rub my nose in the irony of my being victimized by the Rosenthal effect (finding or seeing what you expect), right after having contrasted that with Occam's razor (the simplest interpretation for all of the data).

Similarly, the authors of this study, if that news release is completely accurate, might appear to have neglected that chlorides, in addition to being more soluble, have much greater freezing point depressions than sulfates (more than 50C vs. less than 5C). Therefore, preferential frost leaching of chloride, on which Knauth and I published in 2002 and 2003 (in Icarus and JGR) might seem a more "Mars-friendly" explanation than rain or mist.

A couple of author's quotes from that news release: "Our study suggests that Mars isn't a planet where things have behaved radically different from Earth" and "It seems very logical that a dry, arid planet like Mars with the same bedrock geology as many places on Earth would have some of the same hydrological and geological processes operating that occur in our deserts here on Earth". In this regard, after weeks of 110+ degree (= 43C) days, Phoenix had its first seasonal dust storm last night. Do dust storms make Phoenix, Arizona hydrologically comparable to the Phoenix lander site, Mars? Perhaps not.

-- HDP Don

[ngunn]

I thought you'd have something to say here about the unreliability of earth analogues.

[dburt]

In other words, you knew I wouldn't be able to resist.

-- HDP Don

[marsbug]

As for Mars, and impacts, you need a planetary-scale impact that will deposit an impact sheet AT LEAST 1 m thick. That will keep the atmosphere hot for 1 year, and the surface warm for 10 years. A 10m impact sheet is worth about 30 years in the atmosphere and 300 years at the surface, and a 100m sheet is 1000/10,000 years

But when you look at the size of impact require to acheive this, the mind boggles. Isidis and Hellas are the sort of thing we need.

The impact in the thread next door would probably meet the requirements