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What if Mars Had Been Closer and Venus Farther?

  1. Jun 14, 2008 #1
    This is a purely hypothetical question, of course -- but what if our solar system had evolved with Mars and Venus switched, with each occupying the other's orbit?

    Would each have ended up more Earth-like today as a result?
  2. jcsd
  3. Jun 16, 2008 #2
    these are the awesomestquestions because they deal in purely hypothetical circumstances.
    Now what's great aboutmother earth is that we are in a region where thesun's rays are not too hot nor too cold. Mercury is way too close to the sun to be able to support life,venus is pretty close and has issues of its own but WE are in a zone where it hits us just right. Of course in millions of years when the sun will be burning more fuel and consequently becoming larger, thezone will move farther away (closer to mars) and then they will have the more ideal and pristine conditions. So, now responding to your question if venus and mars had been closer to where we are now 1 our gravitational fields would be kind of screwy (imagine what would happen to the tides). But then we might have friendly, or unfriendly neighbors. Cool, huh?
  4. Jun 16, 2008 #3
    Hi rubecuber,

    Well, I was thinking that Mars with its smaller size, would have a faster rate of cooling, which could slightly offset the higher influx of solar radiation coming in at the current Venus orbit. Perhaps if it had been in the current Venus orbit, Mars' core wouldn't have cooled off quite so fast, and could have provided a magnetosphere (can I assume it had one in the past, when its core was molten?) So from that, there would have been less solar wind erosion of its atmosphere. With a slower rate of cooling due to the hotter orbit, Mars would have stayed tectonically active for longer. There could then have been liquid water to support life, and a CO2 atmosphere which might have then been transformed into an O2 one, by similarly evolved photosynthetic bacteria.

    Meanwhile, Venus sitting in Mars' current orbit would have received less sun, and perhaps its colder position would have meant that the current noxious substances (sulfuric acid clouds, etc) would have instead been precipitated onto the surface. Venus' Earth-like gravity (.91G) and its colder orbit would have kept water from from boiling away, so that it would have been covered with oceans today. Photosynthetic bacteria could have then evolved in its oceans, to transform a CO2 atmosphere into an O2 one. After awhile, Venus would have ended up looking somewhat like the polar regions of Earth today.

    Does anyone else care to provide their speculations or informed guesses on what would have happened if Mars and Venus had been 'switched at birth'?
  5. Jun 17, 2008 #4
    What exactly are you asking? If Venus and Mars switched places at the birth of the solar system, the planets would have evolved in much the same way. If you are asking what would happen if we moved {if we could} Venus in to Mar's orbit, that is a different question.
  6. Jun 17, 2008 #5
    I'm asking what would have happened if each planet had started out in the other's orbit.

    So you feel that swapped orbits would have had no effect on their past evolution?

    For example, comparing Venus to Earth, do you feel that the differences we see today are entirely due to differences in composition, and that the closer orbit of Venus had nothing to do with this?
  7. Jun 18, 2008 #6
    Correct. When the solar system was initially formed and Mar was in Venus' spot, and vise versa, I don't see how the individual planets evolution would be different.
    Not entirely. The planets we see now are a direct result of 4+ billion years of evolution. There are several factors that all come together to create what we see. The chemical composition does play a part, (for example, if Venus didn't have so much CO2, it probably wouldn't be so hot.) But, I don't think it is the determining factor. Chemical composition is related to its orbit. Closer planets tend to be terrestrial, were as outer planets are made of mostly gas.
  8. Jun 18, 2008 #7
    Mars would remain uninhabitable, the liitle atmosphere it has would be blown off by solar heat.

    Saturn is an interesting proposition, out in the orbit this earth size world might develope life

    Last edited: Jun 18, 2008
  9. Jun 18, 2008 #8


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    Certainly it seems that were the mass of Mars imposed on Venus today (and vice versa - perhaps a better phrasing of the predicate), one wonders if it would have sufficient gravity to resist the solar wind absent a fairly pronounced magnetosphere. (Something that neither planet apparently enjoys in any event.)

    As seen today Mars wasn't able to hold on to its own endowment at its current orbit, much less one would have to think at a more inward orbit to earth - subject to higher energies and intensities from the sun - and not withstanding even the endowment of gases Venus has already evidently enjoyed.

    On the other side of things were Mars to have had greater mass then perhaps its endowment of water and hydrogen would have been retained to a greater degree providing the kinds of opportunities that earth's more fluid surface has enjoyed - insofar as the conveyance and mixing of the elements from tidal churn of the moon. But again the lack of a magnetosphere seems to be a daunting omission in the formation of both Venus' and Mars' histories and makes one wonder if swapping the masses would merely mean today that Venus would have a diminished atmosphere resulting from it's lower gravity and Mars would have a slightly higher atmosphere on substantially as barren a planet as we now observe.

    A more interesting consideration might be the effect on earth of a less massive Venus to the inside. Would a substantial bulk of the CO2 gathered by the Venus of today possibly either have migrated from Venus if captured, or not captured in the first place, and resulted in earth capture instead? Would the earth have had the resources even with it's magnetosphere to sequester that much more CO2 into more carbonates? Would the earth be the same place today? Looking at the fragile ranges of things as we know it I have serious doubts the world would be the same, so if you don't mind please don't go mucking about with switching masses around lest you unleash the Law of Unintended Consequences.
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