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Astronomy/Venus and Mars if they switched orbits


Hi James
Venus has held a special interest for me for awhile, so I am curious to know what happen if Venus swapped orbits with Mars,would oceans possibly form on that planet now that its further from the sun?
I know Venus has like a runaway greenhouse effect making the surface temperatures incredibly hot, but what would happen to the atmosphere once its further away from the sun?
I guess with Mars it would just become a hot barren desert world?

Hi Dimitri,

This simple question is quite complex to answer. There are sophisticated computer programs which attempt to model planetary atmospheres, some of which have had very limited success. So anything I say will be a guess at best.

There are too many unknowns. A planet's climate is based on a complex intermingling of initial composition (of both the atmosphere and crust), mass, distance from the sun, orbital eccentricity, magnetic field, and rotation. That said, I'll assume you mean that the planets swapped orbits "today" (after 4.5 billion years of evolution). I say that because Venus likely lost most of its water because it was closer to the sun. If Venus started out in Mars' orbit, it may have retained some of it.

So if Venus were placed (today) in Mars' orbit, oceans would not form. There's not enough water vapour (or other gases which could easily condense) to form oceans. It would be cooler, but still warmer than Earth. Too hot for carbon dioxide to condense at the poles, for instance. The atmospheric composition would not change significantly.

If Mars were placed in Venus' orbit, it would probably lose the little water it has (through loses in the high atmosphere and interaction with the solar wind). Since it has a thin atmosphere of mostly carbon dioxide, it would have a slight greenhouse effect (compared to the large greenhouse effect Venus has now), so the planet would certainly become hot and barren.

Unfortunately, that's about as far as I'd like to speculate. It would be a good problem to model.

Prof. James Gort  


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James Gort


Questions on observational astronomy, optics, and astrophysics. Specializing in the evolution of stars, variable stars, supernovae, neuton stars/pulsars, black holes, quasars, and cosmology.


I was a professional astronomer (University of Texas, McDonald Observatory), lecturer at the Adler Planetarium, professor of astrophysics, and amateur astronomer for 42 years. I have made numerous telescopes, and I am currently building one of the largest private observatories in Canada.

StarDate, University of Texas, numerous Journal Publications

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