How is Venus atmosphere so thick despite being smaller than Earth and does that mean a Mars sized planet can have a thicker atmosphere?

Venus atmosphere is 93 bar and it is slightly smaller than Earth. So could a Mars sized planet have an atmosphere of say 0.5 bar or more in another solar system if it developed different than Mars? Essentially what I am asking is can a Mars sized planet support a thick enough atmosphere to have liquid water if it developed differently than Mars?

7 Answers

  • 2 months ago
    Favourite answer

    If you look at the atmosphere of Titan, it's actually thicker than Earth's atmosphere as well, and it's quite small, at about 3200 miles. (A bit smaller than Mars, and not much density either.) 

    So yes - a Mars-sized planet *could* support a thick enough atmosphere to have liquid water...

  • 2 months ago

    A planet's atmosphere depends on many factors, size being just one of them. Just as important are the rate of production of gas and the rate at which it escapes into space.

    You didn't specify how long the planet in question must hold it's atmosphere. When gas escaping from the interior of the planet ceases, the planet may retain a thick atmosphere for a short or long time depending on the rate of escape, which in part depends on the size of the planet.

    Don't know why you singled out water, but a planet may have liquids on it's surface of varying compositions including methane, ethane, liquid CO2, water, liquid sulphur, molten rock, or a range of other conceivable substances depending on it's composition, temperature and gas pressure.

  • Brian
    Lv 7
    2 months ago

    Venus have a runaway Greenhouse Effect

  • cosmo
    Lv 7
    2 months ago

    It's not just the surface gravity of the planet, there are a number of other parameters.  One of the most important is the planet's magnetic field, which is generated (or not) deep in its interior and provides (or not) a shield against entrainment of the upper atmosphere by the solar wind.  Mars did have liquid water, but then its magnetic dynamo shut off, allowing the solar wind to blow away most of its atmosphere.

    A big effect for the Earth was the "Moon-forming event", which knocked off a  thousand mile thick layer of low atomic weight outer crust from the Earth.  (It's all up there on the Moon.) This is one of the main reasons the Earth's atmosphere is not as heavy as Venus'.

  • What do you think of the answers? You can sign in to give your opinion on the answer.
  • Anonymous
    2 months ago

    Be mindful  "scientists" are only guessing by what they can see. And Test. Otherwise they do not know.

    We take as gospel, too much of what "science" says.

  • 2 months ago

    Venus is home to a Massive Live Sheild Volcano

    That would in Girth anyway would compete with the Extinct Martian ones

    It constantly replenishes the Venusian Atmosphere with CO2 and Aerosol Gases

    Global Warming Gone Loopy !!

    As well as its closerness to the Sun

    Do you like that word ?

    It is believed that Mars once was more User friendly

    Being Warmer and Wetter

    Its Volcanoes were once live

    A collision the sized of Texas circa 2.5 Billion years ago turned it into the dead Planet it is now

    But given the comparative time, Earth began Evolution 3.8 Billion Years ago

    There is a chance of slightly more Complex life on Mars was imminent

    It would also have had a decent Atmoshpere too with about 80% of Earth's Mass

    After all, Mass is the key to Gravity

    Attachment image
  • 2 months ago

    A Mars-sized planet with a functional geomagnetic shield would be able to retain its atmosphere.  Evidence indicates that when Mars was young enough for that, it also had a thicker atmosphere.

    The main problem (we think) is that for such a magnetic shield, a planet needs a rotating metallic core.  And that requires sustained internal heat.  The smaller a planet, the faster it loses that heat.

    Mars appears to be too small for that to persist.


    The atmosphere on Venus is as thick as it is primarily because of its massive vulcanism.

Still have questions? Get answers by asking now.