Here is what we know of the planet Mars so far:

DIAMETER: 4212 miles

MASS: 6.39 × 10^23 kg

DISTANCE FROM THE SUN: 141.6 million miles

It isn't to say that we haven't found water on Mars, just that liquid water is hard to find on Mars, and it may be because at 141.6 million miles from the sun, Mars is at the very outer edge of the Goldilocks Zone. It doesn't help that its primarily-CO2 atmosphere is thinner than Earth's.

In this alternate scenario, things are a little different. Mars is no longer red, but blue.

enter image description here

Its diameter is 2.6x greater than Earth's, and its mass exceeds Earth's by seven times. Its atmosphere is thicker than Earth's (but nowhere near as much as Venus') and consists not of carbon dioxide, but instead oxygen, hydrogen, helium, methane and water vapor. Nonetheless, its distance from the sun is the same--141.6 million miles. Are these changes enough for Mars' water supply to be full-on liquid?

  • $\begingroup$ This is irrelevant to the question but it's worth noting that life doesn't "need" to be in the Goldilocks Zone. It's best for water-based life, Earthlike bodies, and photosynthesis, but there are plausible alternatives to water, alternatives to photosynthesis (chemosynthesis, radiosynthesis, thermosynthesis, to name a few), and cheaty ways to manipulate the melting and boiling points of solvents (ex. adjusting atmospheric pressure) that can bring life out of the zone entirely. $\endgroup$
    – Zxyrra
    Commented Dec 8, 2016 at 2:36
  • 2
    $\begingroup$ Is a magnetic field present? $\endgroup$
    – Zxyrra
    Commented Dec 8, 2016 at 2:58
  • $\begingroup$ As Zxyrra asked, whether it has a magnetic field may also be extremely important. A magnetic field helps prevent solar wind from stripping the atmosphere away. $\endgroup$ Commented Dec 8, 2016 at 3:19
  • $\begingroup$ Why not simplify the question a bit, and make the planet almost exactly Earthlike: essentially the same mass, composition, rotation, magnetic field, primordial atmosphere, &c? Given that our Mars had a past age of being comparatively warm & wet (with a significant ocean!), I think if life did take hold, we could wind up with a roughly Earthlike biosphere (perhaps by microorganisms from Earth seeding it). The difference is that its tropics might be like Norway or Alaska on our Earth. $\endgroup$
    – jamesqf
    Commented Dec 8, 2016 at 6:10
  • $\begingroup$ @jamesqf Not what I wanted. $\endgroup$ Commented Dec 8, 2016 at 14:17

3 Answers 3


The atmosphere could be supported by such a planet

Here is an answer on how to calculate surface gravity of a planet. Given a radius 2.6x Earth and a mass 7x Earth, the surface gravity would be 1.04g. From that I calculate escape velocity to be about 18 km/s. Given an atmosphere-less surface temperature of ~220K on Mars and this chart from Wikipedia,

enter image description here

you could definitely support an oxygen-methane-water atmosphere. Helium is right about its limit for retention, and might not be retained if the planet was warm enough for liquid water (~275+ K). Hydrogen would likely not be retained. The problem with helium is that there aren't many mechanisms for replentishing atmospheric helium over geological time, so even a small loss rate of helium would completely remove it from the atmosphere in millions to billions of years.

You need to heat the planet up

Mars is rather cold right now. To make it hotter, you need a greenhouse effect. Water and methane are significant greenhouse gasses; as Mars formed and cooled from its primordial boil, a water-methane greenhouse effect could have kept the atmosphere warm enough to support a liquid ocean.

Methane and oxygen are mutually exclusive

Given that methane is natural gas, and burns quite readily, you won't have those two together in the atmosphere. If there is a large amount of both, one little spark (lightning from your water vapour clouds?) would start a fire, which I imagine would burn across the entire atmosphere. In the end, either all the methane or all the oxygen would be removed (whichever was less plentiful) and there would be a lot more carbon dioxide around.

  • $\begingroup$ If methane is a natural gas, then how did the giants (Jupiter, Saturn, Uranus, Neptune) get them? $\endgroup$ Commented Dec 8, 2016 at 2:44
  • 3
    $\begingroup$ @JohnWDailey Methane is natural gas, as in, you burn methane in your furnace or stovetop. I'm just saying it is flammable. The gas giants have methane and not oxygen, Earth has oxygen and not methane. $\endgroup$
    – kingledion
    Commented Dec 8, 2016 at 2:57
  • 3
    $\begingroup$ @JohnWDailey: Having hydrocarbons like methane in the atmosphere appears to be the default state. Methane is extremely common in the universe, while diatomic oxygen (O2, like we have on Earth) is essentially unheard-of. O2 doesn't appear to occur in significant without life producing it, it is just too reactive. $\endgroup$ Commented Dec 8, 2016 at 3:17

Maybe Not

Apparently, Mars regularly loses 30% of it's existing atmosphere due to double pressure solar radiation waves:

According to a 2010 study from the Swedish Institute of Space Physics and the University of Leicester, double solar radiation waves periodically strip away 30 percent of the sparse Martian atmosphere. These waves occur when one solar wave overtakes another to produce a single, more powerful wave.

According to this study,

Mars is constantly losing parts of its atmosphere to space. ... [Researchers] found that Mars's atmosphere does not drift away at a steady pace; instead, atmospheric escape occurs in bursts. The authors relate those bursts of atmospheric loss to solar events known as corotating interaction regions (CIRs). CIRs form when regions of fast solar wind encounter slower solar wind, creating a high-pressure pulse. When these CIR pulses pass by Mars, they can drive away particles from Mars's atmosphere. The researchers found that during times when these CIRs occurred, the outflow of atmospheric particles from Mars was about 2.5 times the outflow when these events were not occurring. Furthermore, about one third of the material lost from Mars into space is lost during CIRs.

During the solar minimum of 2007–08 researchers observed 41 CIR high pressure events.

So, if I understand all this correctly, even if Mars were suddenly given a suitable atmosphere, it would constantly be losing large amounts off into space. Without a replenishing mechanism, soon the atmosphere would be back to it's current feeble state, freezing any water back to ice.

  • 1
    $\begingroup$ Mars has not just been given an atmosphere; it has also been given considerable mass to hold this atmosphere in; may include ozone to shield from radiation as well $\endgroup$
    – Zxyrra
    Commented Dec 8, 2016 at 2:57
  • $\begingroup$ True, more mass, but I'm not clear enough on the physics to know if that is enough to prevent CIRs from stripping atmosphere. I'm not even sure how to figure out exactly what would be needed to keep 100% of the atmosphere in place. $\endgroup$ Commented Dec 8, 2016 at 3:01
  • $\begingroup$ Ideally a thick ozone layer and a magnetic shield, but gravity produced by more mass could still easily counterract most "stripping" $\endgroup$
    – Zxyrra
    Commented Dec 8, 2016 at 3:02
  • $\begingroup$ I was not clear about the part where they said "Mars desperately needed an electromagnetic field". I don't know how strong these CIRs are and what exactly could prevent them from stripping atmosphere. Maybe more gravity is all that is needed. $\endgroup$ Commented Dec 8, 2016 at 3:04
  • $\begingroup$ @Zxyrra I'll have to let people better versed in physics decide. $\endgroup$ Commented Dec 8, 2016 at 3:05

This interesting planet temperature calculator might help you answer this question.

I filled it out with guesses based on your description.

1 solar mass
Distance of 1.524 AU (Mars orbit)
Bond Albedo of 32.00 (little higher than Earth)
Greenhouse Effect: 4.00 (little higher than Earth)

The average surface temperature of your planet: Kelvin: 271 Celsius: -2 Fahrenheit: 28

This is below the freezing point of water on Earth.

By increasing the greenhouse effects to 6 the average surface temperature of your planet: Kelvin: 290 Celsius: 17 Fahrenheit: 63

Which would be fine.

For reference Venus has a greenhouse effect of 200.


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