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There's No Wind Chill On Mars

Posted by Soulskill on from the it's-not-the-cold,-it's-the-aridity dept.

sciencehabit writes: Even though daytime temperatures in the tropics of Mars can be about –20C, a summer afternoon there might feel about the same as an average winter day in southern England or Minneapolis. That's because there's virtually no wind chill on the Red Planet, according to a new study — the first to give an accurate sense of what it might feel like to spend a day walking about on our celestial neighbor. "I hadn't really thought about this before, but I'm not surprised," says Maurice Bluestein, a biomedical engineer and wind chill expert recently retired from Indiana University–Purdue University Indianapolis. The new findings, he says, "will be useful, as people planning to colonize Mars need to know what they're getting themselves into."

22 of 110 comments (clear)

  1. Wind chill on a space suit? by michelcolman · · Score: 5, Insightful

    Wind chill works because of evaporation on the skin, right? I don't think anyone is going to be walking around on Mars outside a biosphere, in a T-shirt. If you're wearing a space suit, wind chill is totally irrelevant or am I missing something?

    1. Re:Wind chill on a space suit? by Chrisq · · Score: 5, Informative

      Wind chill works because of evaporation on the skin, right? I don't think anyone is going to be walking around on Mars outside a biosphere, in a T-shirt. If you're wearing a space suit, wind chill is totally irrelevant or am I missing something?

      Only partially - its also the continual replenishment of cold air against the skin. You don't sweat when you'r really cold.

    2. Re:Wind chill on a space suit? by mysidia · · Score: 5, Informative

      Wind chill works because of evaporation on the skin, right?

      Aside from the affects of evaporative cooling: wind chill also works due to air movement.

      Moving air dissipates heat more quickly than stagnant air.

      By the way.... since there is essentially little or no air on mars... there is essentially no wind, so it follows and is quite expected that there would be no wind chill; however, this is not very interesting, because: humans cannot survive in this environment.

      It is necessary to have an artificial environment that includes air.

      The environment that includes air.... if it is large enough: will be subject to wind chill, whenever a sufficient difference in pressure or temperature from one area another is large enough to cause quick air movement.

    3. Re:Wind chill on a space suit? by Anonymous Coward · · Score: 4, Insightful

      By the way.... since there is essentially little or no air on mars... there is essentially no wind,
      so it follows and is quite expected that there would be no wind chill; however, this is not very interesting,
      because: humans cannot survive in this environment.

      Without assistance.
      It is highly interesting for a manned Mars mission. If temperature doesn't cause an issue you can make the protective-suit a lot more flexible.
      Just because the air on Mars is too thin to be breathable (And lacking oxygen.) doesn't mean that it will be directly harmful to your skin.
      If gloves are optional or could be made very thin then a lot of things will be easier.
      Walking around in scuba gear is preferable compared to walking around in a full pressure suit.

    4. Re:Wind chill on a space suit? by xororand · · Score: 5, Informative

      Unfortunately the atmospheric pressure on Mars (0.6 kPa) is far below the Armstrong Limit (6.3 kPa) at which your blood boils at body temperature.
      https://en.wikipedia.org/wiki/...

    5. Re:Wind chill on a space suit? by Thanshin · · Score: 4, Funny

      Yes. It's unfortunate. It takes away the once in a lifetime opportunity of breathing 96% CO2.

    6. Re:Wind chill on a space suit? by Anonymous Coward · · Score: 5, Funny

      Unfortunately the atmospheric pressure on Mars (0.6 kPa) is far below the Armstrong Limit (6.3 kPa) at which your blood boils at body temperature.
      https://en.wikipedia.org/wiki/...

      I thought the Armstrong limit had to do with how many times you can win a Tour de France without getting busted for doping?

    7. Re:Wind chill on a space suit? by queazocotal · · Score: 4, Informative

      And if you continue reading past the first paragraph - you find that that is only true if the blood is no longer in your body.
      The blood pressure of a live person means the blood does not boil at any pressure, as the pressure inside the blood exceeds the boiling point - even if the skin is under vacuum.

    8. Re:Wind chill on a space suit? by fnj · · Score: 4, Insightful

      The other problem is the entire wind chill factor is still being disputed about, here on earth. I could be -20F outside with no wind and the dry air alone would suck the moisture from your body.

      [raises hand] Nobody, but nobody, who has experienced a cold climate in both still air and high winds disputes the wind chill factor.

    9. Re:Wind chill on a space suit? by michelcolman · · Score: 3, Informative

      Maybe the blood doesn't actually boil, but you may get the bends (vapour bubbles forming in your blood) which will probably be lethal.

    10. Re:Wind chill on a space suit? by fnj · · Score: 4, Informative

      Actually the Armstrong limit describes the PRESSURE at which water and similar fluids boil at body temperature. Yeah, if you withdrew some of your blood and put it in an open container, it would boil. But the blood in your blood vessels is not at outside pressure. Arthur C. Clarke had it right in 2001. You can experience a vacuum briefly without the blood in your blood vessels boiling. You do need to mind your eyeballs, mouth, trachea and alveoli though.

      You probably know this already, but the truth of the matter of exposure of the human body to a vacuum is a bit less horrific than uninformed lurid speculation has it. You're not going to last long, but your body does not quickly blow up like a balloon from the blood boiling. There is actual experience of 10+ second exposure.

    11. Re:Wind chill on a space suit? by stenvar · · Score: 2

      Such suits, in fact, exist and have been tested:

      http://en.wikipedia.org/wiki/S...

      They do allow gas exchange between your body and the space outside (vacuum, Martian atmosphere).

    12. Re:Wind chill on a space suit? by rossdee · · Score: 2

      "in the truly -20ÃC temperatures it feels closer to an average winter's day in the UK."

      Except theres no snow, sleet, or rain, so its not really like a UK winters day.

    13. Re:Wind chill on a space suit? by gstoddart · · Score: 2

      Aside from the affects of evaporative cooling: wind chill also works due to air movement.

      I don't know about you, but where I live, by the time they're discussing the wind-chill, there's no 'evaporative cooling'. There's a biting wind which travels through your clothes, pulls the heat from you, and tries to kill you. It also leads to things like frostbite happening faster.

      You're describing the cooling effects of a breeze on a hot day ... you want windchill? Think downtown Chicago in the dead of winter while the wind rips along at a zillion miles per hour.

      I've never heard anybody describe wind-chill for anything less than well below freezing, so there isn't a whole lot of sweat to be subject to evaporative cooling, just having your body heat sucked out of you.

      --
      Lost at C:>. Found at C.
    14. Re:Wind chill on a space suit? by gstoddart · · Score: 2

      The other problem is the entire wind chill factor is still being disputed about, here on earth.

      That sounds like bullshit.

      I've experienced -40C, which oddly enough, is also -40F.

      The difference between wind and no wind at those temperatures is enormous, and can be the difference between your skin freezing in minutes or seconds.

      Wind-chill is only experienced by things which generate their own heat (so it doesn't affect bridges), but if you don't think it affects animals ... well, you've never really seen winter then.

      As far as I know, the only dispute about wind-chill is how, exactly, you calculate it. That it exists and is real isn't really ever disputed.

      --
      Lost at C:>. Found at C.
  2. Wind chill on a solar collector by Anonymous Coward · · Score: 5, Interesting

    Not too relevant for people, but if you're designing a solar collector to warm an underground settlement this is pretty important. You would still need some large mirrors to get enough energy to be useful. But the low atmospheric pressure would dramatically reduce the insulation requirements. Maybe just a couple of layers of reflective foil around the pipework and behind the collector to reduce radiation losses.

    Similarly, if you're planning a high pressure (from a mars perspective) greenhouse this has a real bearing on heat losses.

  3. Re:Global Warming may be the solution by Irate+Engineer · · Score: 2

    Ummm...you need oxygen to burn stuff.

    --

    Left MS Windows for Linux Mint and never looked back!

    Vote for Bernie in 2016!

  4. Re:"People planning on colonizing Mars ..." by burisch_research · · Score: 2

    No joke. Elon's planning to make this happen really quite soon, and I'm inclined to believe him.

    http://en.wikipedia.org/wiki/M...

    --
    char*f="char*f=%c%s%c;main(){printf(f,34,f,34);}";main(){printf(f,34,f,34);}
  5. Still not at all cozy by fnj · · Score: 3, Insightful

    Somebody already beat me with the post about the surface of Mars being beyond the Armstrong limit.

    I'll just reinforce that by pointing out that the atmosphere at the surface of Mars is the same density as Earth's atmosphere at 34,600 m of altitude. Feeling a bit chilly is about the LAST thing you would have to worry about on Mars. Saliva vaporizing from the surface of your tongue, tears vaporizing in your eyes, and fluids evaporating from the alveoli in your lungs will be a bit bothersome if you open your mouth and eyes before you pass out from anoxia. Ever see the space-suit-looking contraption with full helmet that you have to wear in an SR-71? Well, the ceiling of the SR-71 is a good 8700 m below 34,600. Then there's the itsy bitsy detail that Mars' atmosphere is 96% CO2.

    An oxygen mask alone just won't do any good.

  6. Minneapolis or Southern England? by Anonymous Coward · · Score: 2

    These places aren't comparable.

    Average January temperature in Minneapolis: -9C
    Average January temperature in London: 4C

  7. Re:How surprising... not by MancunianMaskMan · · Score: 2

    Mars' atmosphere is .. around 20 mBar ..it's near-vacuum. And vacuum makes for a very good thermal insulator.

    "For all practical purposes" is not correct. The thermal conductivity of a gas is near-independent of pressure down to very low pressures, until the mean free path of particles becomes large compared to the distance to the solid where the heat gets dumped. 20mBar and the MFP is still tiny.
    You need a pretty good vacuum (10^-4mbar or so) in a coffee flask otherwise it doesn't change a thing.

  8. Even without wind chill by Anonymous Coward · · Score: 3, Funny

    Mars ain't the kind of place to raise your kids. In fact it's cold as hell.