MadSci Network: Astronomy |
Joe, After checking all the known planets with atmospheres (including several moons, notably Titan and Triton), it seems that there are two planets that have atmospheres closest to that of the Earth. They are also the planets that have a similar overall composition and origin to our planet: Venus and Mars. Neither one is a dead match, however. Venus' atmosphere is about 100 times denser than the Earth's, and Mars' atmosphere is about 100 times less dense than the Earth's. The things that these two planets' atmospheres have in common with the Earth are the gases that are in them. They all have Carbon Dioxide(making up around 95% of Mars' and Venus' atmospheres and only .00035% of Earth's) Nitrogen, Argon and water vapor in differing amounts. However, neither Venus or Mars have the abundance of free oxygen that is the hallmark of the Earth's atmosphere- owing largely to the presence of plant life. I hope I answered your question Joe. For more information, there is a great in depth discussion of this topic in chapter 13 of the 4th edition of "The New Solar System" edited by J. Kelly Beatty, Carolyn Collins Petersen and Andrew Chaikin, copyright 1999. Nice straightforward question! -Paul Barrett Lead Science Demonstrator Pacific Science Center paul_barrett@pacsci.org
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