Astronomy/astronomy question

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Question
Mercury and Mars have similar surface gravities, yet Mars has a permanent atmosphere while Mercury does not.  Explain why.

Answer
Permanent?...  Who says (or establishes) that today's conditions are "permanent"? (as in forever)?
Both planets have no magnetic field to protect their atmospheres, so eventual solar wind erosion will occur in both cases.  Mercury being much closer of course would experience a much higher velocity solar wind so one would expect to find a near-zero atmosphere on Mercury after 4.5 billion years of solar wind bombardment.

Mars, on the other hand, experiences a weaker solar wind but it's atmosphere is also very tenuous.  But Mars still has frozen solid carbon dioxide ice on it's surface (polar caps and permafrost soil) which slowly sublimates up into the atmosphere providing a very thin CO2 atmosphere at the PRESENT time period.  But are we now, at this time frame, the final end result for the Martian atmosphere???  Probably not.  Eventually all the carbon dioxide ice will sublimate into the atmosphere and the ever-present solar wind will strip it away, and in the end (a very short 100 million years from now compared to 4.5 billion years).... Mars will  have, like Mercury, a near-zero atmosphere also.  Mars, being farther and colder than Mercury, just got lucky to have a reservoir of dry ice still present on the planet in this time period, which I doult will last "forever".  So forget the idea of 'permanent'.
Hope this helps,
Clear Skies,
Tom Whiting

Astronomy

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Tom Whiting

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Astronomy has been my hobby/pasttime for over 50 years.  Currently own 3 telescopes, the largest of which is a 30 inch Newtonian truss Dob that is portable.I taught Astronomy/Meteorology at the University Level for 13 years before retiring in 1995. Being retired and home most of the time, I am able to answer all questions relatively quickly, unless it's a new moon weekend with good observing conditions.  No astrology questions please, or questions about alleged UFO picture identifications.

Experience

Experience: Astronomy has been my hobby and study for over 50 years. We currently now own a 30 inch portable telescope (Updated - Pennsylvania`s largest portable telescope). It can be seen on our website at:http://www.velocity.net/~bwhiting and also attend several regional starparties during the year, and have been on 5 total solar eclipse expeditions.

Organizations: President, Erie County Mobile Observers Group for over 15 years.

Publications: Wrote the "Over Erie Skies" newspaper article in our local newspaper for 11 years (1975-86).

Education: Masters Degree- Taught at the University level for 13 years. Retired 20 years -USAF Pilot - KC-135 with 180 combat missions;  Also Eagle Scout, Philmont staff 2 Yrs, Order of Arrow Lodge Chief, Ham Radio (inactive).

Awards: two discoveries: The mini-coathanger asterism in Ursa Minor (the little dipper) And the mini-ladle- another asterism in the bowl of Ursa Minor. Clients: Currently President of the ECMOG as mentioned above.

Education/Credentials
BS  Metallurgical Engineering Grove City College, PAMaster's Degree, Gannon University, Erie, PA Also retired USAF pilot, 20 years.

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