Tsarren <tsarren at alyra.org> Sent by: dragaera-bounces at dragaera.info 04/07/06 12:02 PM To dragaera at dragaera.info cc Subject Re: Speculative Planetary Statistics for Dragaera (Math help?) >On Fri, Apr 07, 2006 at 10:43:08AM -0700, Jon_Lincicum at stream.com wrote: >> >> I'm speculating that gravity on Dragaera lighter than Earth, based on the >> following: >> >> 2. At the same time, lighter gravity means that the atmosphere is likely >> to be thicker than ours (so that the air-pressure is able to sustain >> life), > >I didn't think that was a given - dunno why Venus has such a dense atmo, but >Mars certainly doesn't. On first glance there are a variety of factors >besides more gravity = more ability to retain atmo that affect density: >http://curriculum.calstatela.edu/courses/builders/lessons/less/les3/press.html Yes, but neither Mars nor Venus are able to sustain human life. My point here was not that the gravity had to be higher to retain the atmosphere (which has as much to do with the presence of a magnetic field to protect the atmosphere against the solar wind) than it was to say that given the same volume of air, at a reduced gravity, the air pressure will be lower. Now, the range of air pressure needed to sustain human life is fairly broad (for example, while sea-level psi on Earth is about 15 psi, astronauts can survive at an air pressure of around 6 or 7 psi, as long as the concentrations of oxygen are high enough) but the proportions of oxygen/nitrogen/CO2 on Dragaera would need to be about the same as on Earth, or we would see some dramatic differences. For example, if the oxygen level was 40% on Dragaera, rather than the 21% we have on Earth, then everything would be much more flammable. Forest fires would rage out of control with the slightest encouragement. At the same time, a substantially higher partial pressure of CO2 would be toxic to humans, and cause health and breathing problems. As the page you referenced says: "The more the mass of the planet, the more gravitational pull it exerts on molecules of gas. This pull makes the larger atoms, such as nitrogen and oxygen, heavier than the tiny hydrogen atoms, and keeps most of them near the planet's surface." If we postulate a lower gravity on Dragaera, we can therefore see that the overall volume of the atmosphere will have to be larger in order to provide the same propotions of gasses at the planet's surface. This likely would mean that the planet would have a stronger magnetic field than we do on Earth (in order to retain the greater volume of air). This is likely to mean the concentrations of liquid iorn in the planet's mantle and core is more substantial than it is on Earth, and that therefore the planet's density will likely be higher then ours. Majikjon