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 Mars' Atmosphere

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Starmonger



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PostSubject: Mars' Atmosphere    Tue Aug 23, 2011 5:15 pm

If Mars didn't have enough gravity to maintain its Atmosphere how did it develop one in the first place? Shouldn't it have evaporated or drifted out into space as it was forming?
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scopeman

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PostSubject: Re: Mars' Atmosphere    Tue Aug 23, 2011 5:18 pm

It's not a binary situation where a planet has enough gravity for an atmosphere or can't hold onto any atmosphere. The major factors are escape velocity at the uppermost levels of the atmosphere compared to the velocity distribution of the molecules at those altitudes, and the rate of replacement. A molecule moving faster than escape velocity in the uppermost reaches of the atmosphere has a good chance of escaping the planet. If the rate of loss is greater than the rate of replacement, the atmosphere will thin until the two are equal.

The replacement rate also varies over time. Mars was more volcanically active in the past. Also, the rate of bombardment by asteroids and comets was higher in the past. Both of these mean that the replacement rate of atmosphere used to be higher.
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TomK

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PostSubject: Re: Mars' Atmosphere    Tue Aug 23, 2011 5:19 pm

And maybe the presence of iron, and massive volcanoes indicate that Mars was capable of having a stronger magnetic field at one time.

I don't think that it has ever been concluded, but some of the pieces are there.
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AstroJunkie
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PostSubject: Re: Mars' Atmosphere    Tue Aug 23, 2011 5:20 pm

TomK wrote:
And maybe the presence of iron, and massive volcanoes indicate that Mars was capable of having a stronger magnetic field at one time.

I don't think that it has ever been concluded, but some of the pieces are there.

It also isn't concluded if a magnetic field would have been a major factor affecting atmosphere loss. What is certain is that lower mass means Mars would have lost atmosphere more easily than Earth (and Venus as well) with a tenth the mass of Earth it just can't hold onto atmosphere as effectively.

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TomK

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PostSubject: Re: Mars' Atmosphere    Tue Aug 23, 2011 5:22 pm

^ this Cool
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