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PostPosted: Sat Apr 25, 2015 8:32 pm 
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Having moved to Flagstaff, Arizona, I felt compelled to learn more about Percival Lowell and his theories about Mars. My source was Mars as the Abode of Life (Brohan Press, 1908), which was the final version of a theory most famously developed in Mars and its Canals (McMillan, 1906). Mars as the Abode of Life includes Lowell's attempts to answer (or dismiss) critics of his theories, most notably Alfred Russell Wallace* in his Is Mars Habitable? A critical examination of Professor Percival Lowell's book (1907).

The subject makes for a fascinating study in the history of science. Without radioactive decay, the internal heat of the planets is generated from the mechanical energy of the particles falling together to form them. Without continental drift or plate tectonics, geographic features (mountains and valleys; continents and ocean basins) formed in place as the crust cooled, contracted, and cracked or buckled. Volatiles are lost both by escape at the top of the atmosphere (which is correct) but also by constantly seeping through cracks and fissures into the planetary interior. Craters and maria on the Moon are caused by extensive volcanism, in the past if not recent history.

It's important to remember that up to this point astronomy was conducted by peering through telescopes by eye and recording observations in sketches (like a court reporter). Schiaparelli's canali were accepted as real even by Lowell's critics, because they had been consistently seen and recorded by some of the most able observers using the best equipment under the most favorable conditions available. (Lowell claimed to have a photographic plate capturing their image, but I haven't been able to find a copy.) Lowell was convinced that Mars was featureless and flat, because he'd never been able to observe mountain peaks casting long shadows near sunset, or remaining in sunlight after the terminator had passed.

Google Earth has a set of overlay images of Mars based on Lowell's (and others') hand-drawn maps. It's interesting to toggle between these and the maps generated from spacecraft visiting Mars (the Viking orbiter images are complete and easy to read), to see what he got right and what was just flat wrong.



*Wallace is best remembered for his work on speciation by natural selection, and particularly its effect on the geographic distribution of species (cf. Wallace Line).


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PostPosted: Sat Apr 25, 2015 11:30 pm 
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Cool! What were the main advances by 1908 over the material from 1890 that I posted earlier?

Could you post a link to the Google Earth Mars maps? Those would be extra-handy.

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— Brett Evill

My SFRPG setting, Flat Black

© My posts to this board are copyright under the Berne Convention. They may be quoted on the board with appropriate attribution. They may not be reproduced beyond the board except with explicit permission from me.


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PostPosted: Sun Apr 26, 2015 2:26 pm 
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By 1907/8, the scientific community is pretty much convinced that there is no open water to be found on Mars. The dark patches are re-interpreted as vegetation, and canali have been spotted traversing them. Lowell clings to the notion that they are vestigial sea bottoms; Wallace points out that this is inconsistent with his assertion that the canali are perfectly level (i.e., in hydrostatic equilibrium) from pole to equator. Gone, too, are references to precipitation, except in the formation of the polar caps. The caps themselves are known to be (for the most part) very shallow, because they grow and shrink with great rapidity. Most of what were seen as clouds are now believed to be dust, again excepting the haze seen when the polar caps have their seasonal melt.

The argument over Mars' surface temperature is far advanced, with Lowell using some X-treme Maths (15 pages of calculation) to arrive at a figure not too different from Earth and the rest of the scientific community settling on figures around -35 degrees C. All parties seem to agree on the atmospheric pressure (around 80 mb), though this figure has been revised downwards several times. They disagree on composition, with most of the community backing the spectroscopic studies that found no water vapor present but Lowell contending that these are inaccurate because they have to deal with the water lines in Earth's atmosphere. Everyone seems to agree that carbon dioxide ("carbonic acid gas") is present, but they still seem to expect oxygen and nitrogen to provide major constituents. No one seems to have understood CO2 (vs. water vapor) as a powerful greenhouse gas.

Needless to say, Lowell is still convinced that there is life (indeed, necessarily intelligent life) on Mars; Wallace concludes the opposite. They both explicitly accept that the presence or absence of liquid water on the surface is the deciding factor.

My Google Earth fu is not equal to creating a URL link to the views I'm using. If you open Google Earth, there is a button on the top bar that looks like a ringed planet. It opens a drop-down menu that allows you to substitute Mars maps for Earth. Once there, go to the Layers menu on the left margin and expand the Mars Gallery and Historic Maps tabs. You will want to place the south pole at the top of the view to read the labels, since this is how the planet appeared through the telescope lens.


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PostPosted: Tue Apr 28, 2015 8:19 am 
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Location: the Retirement Coast, NSW, Australia
Thanks, that's very interesting — and I've found the maps with your directions. I'm going to have to continue to send expeditions to Mars in 1877–94.

It is an interesting observation that the astronomers overlooked the CO2–greenhouse warming connection, because Arrhenius had calculated the effect and predicted greenhouse warming from the burning of fossil fuels in 1896. Compartmentalisation of Science, I suppose.

_________________
— Brett Evill

My SFRPG setting, Flat Black

© My posts to this board are copyright under the Berne Convention. They may be quoted on the board with appropriate attribution. They may not be reproduced beyond the board except with explicit permission from me.


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