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SolarSystemGeologist
2007-Nov-08, 02:35 AM
I've heard that the reason Mars lacks a sunstantial atmosphere is because it was peeled way by the solar wind since it lacks a substantial magnetic field. Unless I am mistaken, Venus also lacks a hefty magnetic field, so it's atmosphere should have been blown away aeons ago. What's going on?

Tucson_Tim
2007-Nov-08, 02:39 AM
Venus is much larger than Mars - much closer to the mass of the Earth. Gravity is one factor in retaining an atmosphere.

ETA: Venus is eight times as massive as Mars - approx 0.8 Earth mass

Neverfly
2007-Nov-08, 02:44 AM
From This paper: (http://www-ssc.igpp.ucla.edu/personnel/russell/papers/venus_mag/)


The 'magnetosphere' of Venus that was detected by spacecraft is now known to be an example of an 'induced' magnetosphere. In an induced magnetosphere, the solar wind interacts directly with the planetary ionosphere.

Diagram of interaction. (http://www-ssc.igpp.ucla.edu/personnel/russell/papers/venus_mag/fig1.gif)

From Wikipedia: (http://en.wikipedia.org/wiki/Atmosphere_of_Venus#Magnetic_field)

Due to its slow rotation and its estimated lack of internal thermal convection, Venus has a much weaker magnetic field than that of Earth. As a magnetic field keeps solar wind from knocking particles out of the atmosphere and into space, Earth has kept a relatively large supply of lighter elements in its air. On Venus however, it has been theorized that the much weaker magnetic field (only 0.000015 times that of Earth[23]) has caused lighter gases to be knocked out of the atmosphere, leaving only carbon dioxide and small traces of other elements and molecules.

ETA: I notice that Tucson Tim replied too- My reply doesn't discount his at all- and thanks Tucson Tim for filling the gap I neglected;)

Neverfly
2007-Nov-08, 02:46 AM
Here is a bit about how Mars got clobbered. (http://science.nasa.gov/headlines/y2001/ast31jan_1.htm)

antoniseb
2007-Nov-08, 11:47 AM
I've heard that the reason Mars lacks a sunstantial atmosphere is because it was peeled way by the solar wind since it lacks a substantial magnetic field. Unless I am mistaken, Venus also lacks a hefty magnetic field, so it's atmosphere should have been blown away aeons ago. What's going on?

Notice that both Venus and Mars have a substantially reduced level of light molecules in their atmosphere. The atmosphere of Venus has a 35:1 bias in its deuterium:hydrogen ratio from the Solar ratio (IIRC), which indicates that it's atmosphere used to be MUCH denser, with hugely more Hydrogen, and that it is NOT getting replenished significantly.

neilzero
2007-Nov-08, 05:47 PM
Venus has about the same amount of atmospheric nitrogen as Earth, which might indicate Venus has lost very little nitrogen to the solar wind. Nitrogen is slightly lighter than oxygen.
Venus can lose huge quantities of atmosphere before the surface pressure and surface temperature decrease much. The high temperature encourages out gassing of a planet's crust, the high pressure discourages out gassing of a planet's crust. Mars may not have significant lighter volitiles left in it's crust, while Venus may have retained most of its crust volitiles. Please refute, embellish and/or comment. Neil

Romanus
2007-Nov-09, 04:19 PM
Venus's atmosphere is far too massive--almost a hundred times more so than Earth's--to lose an appreciable amount to the solar wind. Venus's escape velocity is more than twice that of Mars, which also means that it takes four times as much energy to strip a molecule away from it.

More relevant to the title: probably, especially if volcanic outgassing is current. The interplay between gases added and subtracted from the atmosphere through surface reactions would be a fascinating area of study, but unfortunately I don't think we know enough about the surface chemistry to get very far ATM.