
Originally Posted by
questioner1
I read that venus's atmosphere is 81 times as dense as earth's, even though earth's gravity is a bit higher, and venus is a bit closer to the sun, causing the escape velocity of venus to be higher.
The escape velocity of Venus is lower than that of the Earth because the
earth's gravity is a bit higher.
Escape Velocity Earth 11.2 km/sec
Escape Velocity Venus 10.3 km/sec
Moreover, escape velocity generally refers to the velocity that must be attained by an object departing from the surface. At higher levels it becomes progressively lower. Since Venus's atmosphere is not only dense, but thick, the escape velocity at the nominal top of Venus's atmosphere will be even less, proportionally, than at the top of Earth's atmosphere.
The atmosphere is denser primarily because it is more massive. The mass of the Venusian atmosphere is approximately ninety times as great as that of the terrestrial atmosphere. This is mainly bacause on the Earth the bulk of the carbon dioxide has been removed by biological, physical and chemical activity. Thus carbon is trapped in biomass, dissolved in water, and - the most relevant - trapped within carbonates by either biological action or chemical precipitation.
And this also gives me thee question: why is mars' atmosphere so much less dense than earth's? Is it just because of lower gravity? or are there more variables?
This is one of the important reasons. Other issues relate to the absence of any significant magnetic field. Without the field the impact of the solar wind on the upper layers of the Martian atmosphere erodes it over time. At present the temperature of the planets surface is important, since much of the atmopshere is tied up in polar ice fields of carbon dioxide, which undergo seasonal and longer term changes.