There's No Wind Chill On Mars 110
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."
Re:Wind chill on a space suit? (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.
Re:Wind chill on a space suit? (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.
Re:Wind chill on a space suit? (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/... [wikipedia.org]
Re:Wind chill on a space suit? (Score:5, 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.
Re:Wind chill on a space suit? (Score:3, Informative)
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.
Re:Wind chill on a space suit? (Score:5, 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 [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.