If Venus were swapped with mars?

[NERVAfan]

Mars-in-Venus's-orbit wouldn't be habitable due to its low gravity & lack of magnetic field - it would lose air and water (likely faster than in reality due to being closer to the Sun).

Venus in Mars's orbit... I don't think anyone really knows. Its higher gravity might mitigate the loss...

[KerikBalm]

Venus can't form oceans unless water is introduced from somewhere else.

Water vapor in a planet's upper atmosphere can be split into hydrogen and oxygen by high-energy radiation. Because the hydrogen is so lightweight, it may be moving fast enough to escape the planet's gravity. This means that over geologic time, planets that can easily retain water vapor will lose water from their atmospheres.

The only reason Earth doesn't lose its water is because it has an atmospheric cold trap: basically, Earth's stratosphere is so cold that the water vapor freezes out and doesn't reach the exosphere.

When Venus's original oceans boiled, the resulting water vapor was lost to space. Its current atmosphere is pretty much bone dry.

Well, not just that cold trap, but Earth's magnetic field comes into play again... not only does it shiel us from the solar wind, but it helps deflect hydrogen so that the water vapor that is split into O- and H+ can be reformed, the O+ would naturally stay with Earth, and the H+ can be retained thanks to its care an te manetic field.

To get an habitable Venus or Mars (looking long term achievement and habitability), both planets would need a large moon that would knead their cores starting a dynamo (to create a magnetosphere protecting the atmosphere from solar winds, and the surface from lethal levels of radiation), stabalizing their wobble, and breaking Venus' near tidal lock with Sol.

tl;dr moons have more effect on planets than location

We don't know that you'd need a moon. According to some theories, to get plate tectonics, you need significant amounts of water.

Venus would have had a runaway greenhouse very early - due to Water vapor, not CO2. The water was lost, the plate tectonics (if it had any) stopped, CO2 accumualted, while the H2O was lost.

Rather than having moving tectonics plates with subduction and new plate being formed, it seems venus has periodic cataclysmic resuracin events. Maybe the internal dynamo is tied to having tectonic plates?

I tend to think venus would have been habitable if it formed where Earth is now.

And the sun has grown hotter, Earth was in the middle of the habitable zone, now its in the inner edge. Mars would be not nice if moved there now.

Meanwhile, mars where it is now is approaching the outer edge of that zone... but that runt of a planet has too little mass and has lost too much water (would lose even more if it was warmer).

If ~4.5 billion years ago, mars and venus were swapped... venus could start looking quite nice right now....

But if they were swapped now... that planet has almost no water left... even moving it out ot mars wouldn't render it habitable.

co2 dint help to prevent h2 escape on venus. With mars gravity this effect would be even faster.

I guess the main venus issue who remove all the water of venus was due high amount of radioactive materials in its core.

These mean that the core never get cold enoght to become solid, so never had a magnetic field to avoid the H2 escape.

Also the low rotation speed of venus is also a mistery.

#1) its H+ not H2. H2 was lost on earth too. 2x H+ from the photolysis of water is different

#2) its not a matter of the core being cold enough to have a solid core... earths core is solid due ot the pressure.

Both mars and venus have molten interiors... Venus probably has a solid inner core like Earth.

Its core seems to be hot, but that heat escapes in cataclysmic resurfacin events, rather than the continuous cycling due to plate tectonics on Earth.

[Sigma88]

I think you need to give us a little more parameters to speculate upon.

Formed? If whatever planet formed out where mars is now would accrete the same material as before and it would still be the same. Only difference in your idea would be a name swap. Need to specify what would be different, or at what point in time to magically swap them.

That's not the only difference, for example we would be calling venus the god of war after the red color of venus as seen from earth (resembling blood)