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Mars Space Science

There's No Wind Chill On Mars 110

Posted by Soulskill
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."
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There's No Wind Chill On Mars

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  • by Anonymous Coward

    Meteorologists will lobby against colonization. The weather reports on Mars simply wouldn't be exciting enough without wind chill.

  • by michelcolman (1208008) on Wednesday June 11, 2014 @04:26AM (#47210375)

    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?

    • by Chrisq (894406) on Wednesday June 11, 2014 @04:33AM (#47210387)

      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.

      • by gstoddart (321705)

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

        LOL ... depends on the humidity.

        I was in a coastal area in late summer once ... the air temperature was enough to be chilly, but the soupy humidity meant I was sweating.

        I didn't think that it was actually possible to be cold and sweating at the same time, but 90+% humidity and a temperature just below comfortable room temp showed me otherwise.

        Now, I wasn't 'really' cold as you say ... b

    • by mysidia (191772) on Wednesday June 11, 2014 @04:38AM (#47210407)

      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.

      • by Anonymous Coward on Wednesday June 11, 2014 @04:55AM (#47210481)

        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.

        • by Anonymous Coward

          Mars is known for kicking up some pretty severe dust storms and dust devils have been recorded. None of which would be possible if there was no wind.

        • by xororand (860319) on Wednesday June 11, 2014 @05:32AM (#47210593)

          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/... [wikipedia.org]

          • by Thanshin (1188877) on Wednesday June 11, 2014 @05:39AM (#47210617)

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

          • by Anonymous Coward on Wednesday June 11, 2014 @05:44AM (#47210635)

            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/... [wikipedia.org]

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

          • by queazocotal (915608) on Wednesday June 11, 2014 @06:16AM (#47210787)

            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.

            • Re: (Score:3, Informative)

              by michelcolman (1208008)

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

              • by TheCarp (96830)

                While that might happen, it would also be the least of your worries, from the same article:
                "no amount of breathable oxygen delivered by any means will sustain life for more than a few minutes"

                and by the least of your worries, I mean....in the short period before you lose consciousnous.

                • I think the original comment posited that you might be able to have some kind of modified SCUBA suit instead of a full space suit. Perhaps a face mask with a hose leading to an oxygen tank but keeping your skin either exposed or covered with minimal material. Of course, the atmospheric pressure might be so low that this would be uncomfortable or could even result in injury. As a comparison, I looked up the pressure on the top of Mount Everest and got 58 kPa which is far above Mars' 0.6 kPa. It's quite p

                  • by mlyle (148697)

                    For one, the pressures still need to work out that you can move your chest to breathe, if you're just going to wear a mask/helmet.

              • by RockDoctor (15477)
                You'll probably die of suffocation from the (multiple, at least one per lung) air embolisms before you get around to noticing the bends.
          • by fnj (64210) on Wednesday June 11, 2014 @06:56AM (#47210939)

            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 [nasa.gov] 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.

          • by invid (163714)
            So I'm not going to be able to walk around in shirt sleeves after taking an oxygen pill? Bummer.
        • by stenvar (2789879)

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

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

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

          • by Sentrion (964745)

            From your Wikipedia link: "The human body can briefly survive exposure to the hard vacuum of space unprotected,[2] despite contrary depictions in some popular science fiction. Human skin does not need to be protected from vacuum and is gas-tight by itself. Human flesh expands to about twice its size in such conditions, giving the visual effect of a body builder rather than an overfilled balloon."

            Next thing you know the FDA is going to be pulling vacuum chambers after fattys have used them to take selfie's t

        • The pressure is too low. If you pour a cup of water on the Martian surface it will immediately start to boil due to the low pressure. You really don't want your bare skin exposed at all.

      • by gstoddart (321705)

        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 whi

        • by mysidia (191772)

          so there isn't a whole lot of sweat to be subject to evaporative cooling

          Your skin is made of mostly water and always contains exposed moisture... unless it's frozen, cold air is very dry, and being bundled up with warm clothing can even increase the amount of moisture, so there will always be evaporation removing heat and moisture being replaced with cold air as air pressure fluctuates due to the wind.

          However.. wind definitely does improve thermal conductivity, by increasing your contact with air p

    • by Anonymous Coward

      Wind chills main effect lies in conduction. The rate of heat transfer from one medium to another is based on the temperature difference. The greater the difference the higher heat transfer. If you have stale air around you a temperature gradient will form and the transfer of heat from you to the air will decrease. If the air moves, the stale warm air will be replaced with cold air keeping the heat loss constant and higher than in the case of no wind flow.

    • Not true. They've known for decades you only need an oxygen mask and a good winter coat -- no space suit required.

    • 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?

      Windchill has nothing to do with sweat. It's more like stirring a pot of spaghetti sauce to make it heat up faster. You're helping the heat diffuse faster. Your body sweating is designed to take advantage of the process, but it would still happen with our without the sweat.

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

      Wrong. The phenomenon know as "windchill", and is represented by "windchill factors" and such, has nothing to do with evaporation. It is the effect of forced convection on heat removal, the windchill tables were generated by examining the removal of heat from a dry cylinder. Evaporative cooling is an entirely separate phenomenon.

      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?

      Does your space suit need to only provide pressurized air, or must it be a parka too? This is an important question for designing and wearing the darned things.

      According to the actu

  • by Anonymous Coward on Wednesday June 11, 2014 @05:01AM (#47210503)

    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.

    • by fnj (64210)

      Mod parent up. Good points.

    • by stenvar (2789879)

      I assume they'd be dependent on electrical solar panels, and those work less efficiently the warmer it gets.

    • Wind chill does not affect inanimate objects. Yes they might cool down to the ambient temperature faster but they will never go lower than the ambient temperature regardless of the wind speed. Wind chill is what it "feels" like and last I check solar collectors don't feel.

      http://www.nws.noaa.gov/om/win... [noaa.gov]

      • by EvanED (569694)

        Wind chill does not affect inanimate objects. Yes they might cool down to the ambient temperature faster but they will never go lower than the ambient temperature regardless of the wind speed.

        The second half of the second sentence doesn't imply the first sentence. If you have something heated to above ambient (e.g. a structure meant for living), a wind chill absolutely will cause you to spend more heating it.

        "Wind chill won't cool thing below the actual temperature" is (almost) a solid statement. "Wind chil

        • by EvanED (569694)

          Incidentally, I should point out that wind chill, as it's measured in the US, tries to incorporate effects other than just an increase in the rate at which the warmed air is swept away from something warm by the wind. Those effects, e.g. facts dealing with the fact that your skin is wet and the air is dry, will not apply to solar panels.

      • by nedlohs (1335013)

        Wind chill doesn't care if something is animate or not.

        A hot inanimate rock will cool faster in the presence of a wind chill than without (holding the actual temperature constant).

        4 year old children have worked this out, as evidenced by them blowing on their hot food in order to cool it faster so they can eat it faster and get back to doing far more important things.

        How do you think the fan in a computer manages to keep the inanimate cpu from overheating?

  • We could get a shitload of fossil fuels and take it there (perhaps with a really -long- petrol pump pipe) and burn it off in the atmosphere, perhaps by driving lots of 4x4 SUV's. That should help ensure that Martian average temperatures rise nicely by 1 or maybe even 2 degrees Celsius in only a century.

  • Mars' atmosphere is about 1.5 % of Earth's atmospheric density. It's around 20 mBar, or eight times too thin for sustaining life even if it was pure dioxygen. For all practical purposes it's near-vacuum. And vacuum makes for a very good thermal insulator.

    • Mars' atmosphere is about 1.5 % of Earth's atmospheric density. It's around 20 mBar, or eight times too thin for sustaining life even if it was pure dioxygen. For all practical purposes it's near-vacuum. And vacuum makes for a very good thermal insulator.

      Well, yes, but then the thin atmosphere doesn't interfere as much with radiative effects. If this were not so, Mars would be hot because of the continuous radiation input from the Sun, retained by the rock.

      • Except that Mars is much further away from the Sun than we are (1.5 times as far) and so gets much less radiation from it.

        • by arth1 (260657)

          It's also much smaller than Earth and Venus, so the area exposed to the sun (from the sun's point of view) is around 12% of Earth's. So it gets much less heat.
          And light. The images we see from Mars are not what we would see if we were there - the cameras are adjusted for less light, and exposure pushed up so we can see things clearly.

          I wish we would ditch the Mars efforts, and instead look at more interesting destinations like Venus (floating platform habitats) and Titan. If it's just rocks we want to

          • by mlyle (148697)

            > It's also much smaller than Earth and Venus, so the area exposed to the sun (from the sun's point of view) is around 12% of Earth's. So it gets much less heat.
            And light.

            It's dimmer on Mars because of the inverse square law, not because of Mars being smaller. Mars being smaller doesn't have much of a direct effect on temperature, either.

            > The images we see from Mars are not what we would see if we were there - the cameras are adjusted for less light, and exposure pushed up so we can see things clear

    • 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.

      • by Jesrad (716567)

        I seem to remember the thermal conductivity of an ideal gas is directly proportional to the molar density times molar heat capacity, so this sounds very counter-intuitive...

  • Mmmm no. Southern England may be at the same latitude as Minneapolis, but because of the North Atlantic Drift (branch of the Gulf Stream) the climate is very different. -20C is generally not encountered in Southern England even on a very cold night in a very harsh winter.

    • Dear Lord... so I followed the link. It even says "Summer afternoons in the tropics of Mars might even feel as comfortable as an average winter day in the south of England" in the paper's abstract. Tsk.

  • The real use for this info is understanding and designing for thermodynamic exchanges with the Martian atmosphere. The useful takeaway from this article is that heat dissipation from a source will be dominated by infrared emission rather than contact exchange with the atmosphere. Useful knowledge for the design of electronics, pressure suits, and habitats.
  • by fnj (64210) on Wednesday June 11, 2014 @06:32AM (#47210863)

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

    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.

  • There's no wind chill on Mars because nobody sweats there.

  • by Anonymous Coward

    These places aren't comparable.

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

    • As a Minnesota resident I also don't find their statements particularly comforting. An average Minnesotan winter day is still pretty F'ing cold, especially if they are allowing for the wind chill.
  • There is almost no air pressure on Mars. You might enjoy the temperature for the minute or so until you body fluids start to boil. Then the experience would change.
    • by tibit (1762298)

      I didn't know the body fluids had a timer and had to wait until it expires. Surface moisture on all of our body's surfaces exposed to the atmosphere evaporates plenty even in standard conditions [wikipedia.org]. At pressures below the Armstrong limit [wikipedia.org] , there'll be boiling of water at the surface, but that's not the end of the world. Some of the critical fluids inside of your body most definitely are not at ambient pressure. Hypotension [wikipedia.org] let loose will kill you :)

      Your lungs certainly don't take lightly to the surface boiling

  • So, what is the wind chill on Venus? Would a very dense, hot atmosphere have a wind chill?
  • Isn't wind chill a lower apparent temperature due to increased evaporative cooling caused by moving air?
    When the atmosphere is of such low pressure than water can't maintain a liquid state, as soon as any skin is exposed, all surface water will evaporate and suck the heat away with it.

    Assuming your head is still sealed so you've got air to breathe, it also wouldn't be nice having 1 bar of pressure trying to suck your blood through your skin.

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