2 years, 10 months ago
about Venus
What keeps the atmosphere of planet Venus in place?
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M$2 Answers
The atmosphere of Venus, like that of any other planet, is kept in place by gravity. The extremely high temperatures at the surface of Venus cause its atmosphere to expand somewhat, but the atmosphere is already gaseous (about 97% carbon dioxide, with almost no water vapor) and cannot evaporate. Nevertheless, there is a steady slow leakage of the atmosphere to space as atoms (usually in the form of charged ions) are accelerated to escape velocity. The solar wind contributes to this effect, and the total rate of loss from Venus's atmosphere is estimated at about 10^25 ions per second.
To put this number in perspective, just over 6 x 10^22 (Avogadro's number) CO2 molecules, with a total of 1.2 x 10^23 atoms which can be ionized, weigh a total of about 14 grams. If the 10^25 lost ions per second came entirely from the dissociation of CO2, the total weight would be a bit more than 1 kilogram. This corresponds to a mass loss rate of about 3.5 x 10^6 kilograms per year. The total mass of Venus's atmosphere is about 4.8 x 10^20 kilograms, so at the current rate of loss it would take about 1.4 x 10^12 years for Venus to lose 1% of its atmosphere.
To put this number in perspective, just over 6 x 10^22 (Avogadro's number) CO2 molecules, with a total of 1.2 x 10^23 atoms which can be ionized, weigh a total of about 14 grams. If the 10^25 lost ions per second came entirely from the dissociation of CO2, the total weight would be a bit more than 1 kilogram. This corresponds to a mass loss rate of about 3.5 x 10^6 kilograms per year. The total mass of Venus's atmosphere is about 4.8 x 10^20 kilograms, so at the current rate of loss it would take about 1.4 x 10^12 years for Venus to lose 1% of its atmosphere.
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M$
Oops! Avogadro's number is 6.02 x 10^23, not 10^22. The rate of mass loss is therefore an order of magnitude less than stated above, or 3.5 x 10^5 kg/yr. Another way to look at this is that by the time the sun becomes a red giant in about 5 billion years, Venus will have lost about 0.0036% of its present atmosphere.
http://scienceworld.wolfram.com/physics/AvogadrosNumber.html
@davepamn
I think it would still be very hot due to its closeness to the sun, but it would be more like a dry, baked rock, rather than a hot furnace that it is now.
Also, there would be extreme differences between daytime temperatures going into few hundreds degrees C above zero, and nighttime when temperature would drop to -100 °C and possibly lower.
Additionally, places that happen to be permanently in shadow for whatever reason, would be extremely cold regardless of the surroundings, especially if these regions are close to planet's polar regions. Atmosphere is crucial when it comes to keeping energy, and its transfer and circulation through planetary environment. Without atmosphere, heat absorbed by rocks, i.e. minerals that planet is made of, gets quickly lost.
What would be the temperature of Venus without an atmosphere? Would it be cold like Mars?