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> Air pressure on Mars is very low; at 600 Pascals, it’s only about 0.6 percent that of Earth. > The thin atmosphere also means that heat cannot be retained at

> Air pressure on Mars is very low; at 600 Pascals, it’s only about 0.6 percent that of Earth. > The thin atmosphere also means that heat cannot be retained at the surface. > Once temperatures get below the -40 degrees F/C mark, people who aren’t properly dressed for the occasion can expect hypothermia to set in within about five to seven minutes. Such a thin atmosphere will not transfer heat as effectively as it does on earth, so hypothermia due to exposure to -40 degree Martian air is not as big of a concern as it would be on Earth. Interesting points otherwise, though.

693471 7y ago
Poor understanding of physics are exemplified everywhere these days. It's tiring seeing so many armchair experts trying to take over the discourse with their incessant posturing.
- paulcole 7y ago
  I'm not sure that's a fair characterization of Elon Musk.
  - nolok 7y ago
    Honestly talking about him and his companies is very controversial on HN between the for and against, but I would disagree with you; on almost every PR and marketing pieces and talks he tends to take insane shortcuts.
    - paulcole 7y ago
      > he tends to take insane shortcuts Here on HN we say that is a feature not a bug lol.
- nolok 7y ago
  Isn't convection against conduction high school level physics though ? I know it was here in France a decade and a half ego when I was there ...
  - vonmoltke 7y ago
    Yes, but that assumes most people try to retain that knowledge longer than it takes to pass the final.
    - nolok 7y ago
      Well the details sure, but the general concept ? I have no idea of the basic reproduction number / R0 of any common virus, but I remember the idea of it. Although now that I think of it it's probably a terrible exemple since if people remembered that concept they wouldn't question herd immunity of vaccines. I guess I'm just a bit weirded out.
      - aidenn0 7y ago
        Here's a snippet from a Feynmen talk[1]. He was discussing Latin America, but I think this passage applies equally well to secondary education in the US today: > First, and most serious, I believe, is the almost exclusive teaching and learning by means of pure abject memory. This in no way teaches physics as a science. Nothing is understood; it is only remembered. This in no way satisfies the reasons I outlined for teaching science. Memorization of laws does not permit one to make applications of these laws to new situations; it does not permit one the pleasure of ultimately making scientific contributions; it cannot teach any techniques with the hands. From memorizing, knowledge is not understood, and the beauty of nature is not appreciated. It does not tell how things were found out, or reveal the value of an inventive free mind. > For example, the telescope is an interesting device to make, understand, look through, and play with. It turned men's ideas and minds in new directions. It gave a great impetus to the modern revolution of thought. For a long while it was the sole revealer of the vastness of the heavens and man's modest place in it. But, in Latin America one learns that there are four kinds of telescopes: the Newtonian, the Cassigranian, etc., etc. In the first, the image is virtual and inverted, etc. (I put in all this "etc." because I really don't know how many kinds of telescopes there are, or what their names are, or which way the image is in each kind. But don't underestimate me; I know a very great deal about telescopes – how they work, how to make and use one, their powers and limitations, etc.) The result is that the telescope is lost. There is no more telescope, no lenses, no stars, no eyes, no light – just words memorized without requiring understanding. The examination is passed, for the question was "What are the four types of telescopes?" > I must say immediately that I am not against memorizing. Some things, even many (though nothing special) may be learned by heart; for example, it is good, but not essential, to know by heart 7 x 8 = 56. What I oppose in any teaching philosophy is that the philosophy is used exclusively; but in this case it is especially serious because so little is left of the subject. > ... > When asked what Brewster's Law is, advanced students answer in a flash: "Light impinging on a material of index n is 100 percent polarized with the electric field perpendicular to the plane of incidence if the tangent of the angle of incidence equals the index of refraction." > To these same students I then say, "Look out at the bay from which the sunlight is being reflected. If I look at that reflection through this piece of polaroid and turn it, what will happen?" All I receive are blank stares. No one knows. But I get cries of surprise and delight when they try it and see the reflections getting brighter and dimmer. > This shows something is completely wrong. There is no knowledge whatsoever of nature. With the wrong entrance clue the memorization is useless. These students are like books, no more. I can look in the index of a book under "Brewster's Law" and find a reference equivalent to the students' reply. But in the index I cannot find "sun reflecting on bay." > What do the students know that is not easily and directly available in a book? The things that can be looked up in a book are only a part of knowledge. Who wants such a student to work in a plant when a book requiring no food or maintenance stands day after day always ready to give just as adequate answers? Who wants to be such a student, to have worked so hard, to have missed so much of interest and pleasure, and to be outdone by an inanimate printed list of "laws"? 1: http://calteches.library.caltech.edu/46/2/LatinAmerica.htm http://calteches.library.caltech.edu/46/2/LatinAmerica.htm
- DannyB2 7y ago
  > Poor understanding of physics are exemplified everywhere these days. Please allow me to quote former vice president Dan Quayle... https://en.wikiquote.org/wiki/Dan_Quayle https://en.wikiquote.org/wiki/Dan_Quayle Mars is essentially in the same orbit. … Mars is somewhat the same distance from the Sun, which is very important. We have seen pictures where there are canals, we believe, and water. If there is water, that means there is oxygen. If oxygen, that means we can breathe.
  - not_a_cop75 7y ago
    Oxygen can be harvested from the water, so in that sense he's not wrong. It seems like everyone wants to make every politician into an idiot.
    - antonvs 7y ago
      The Mariner 4 probe showed that there were no canals on Mars, and no open water, by 1965. Quayle's knowledge on the subject was over two decades out of date at the time, and he was supposed to be in charge of the space initiative. Quayle was not a smart man, even by the standards of politicians.
zeristor 7y ago
That’s one of the things I’m curious about regarding the Curiousity rover’s RTG. How efficient is convection cooling in order to maintain the thermal gradient to generate electricity? It has radiator fins, so I assume that’s the main form of cooling over radiation; but with such a thin atmosphere I wouldn’t have that it could take away that much heat.
- cbanek 7y ago
  Many deep space probes in vacuum have RTG's as well (like Voyager), and they can radiate the heat just fine. Also, over time of course the amount of power and heat they generate lessens.
  - jandrese 7y ago
    Isn't the power reduction due to radioactive decay of the fuel? Not that the radiators become less effective over time.
    - cbanek 7y ago
      Yes, but RTGs are not particularly efficient, so much of the energy is heat. From wikipedia (https://en.wikipedia.org/wiki/Radioisotope_thermoelectric_generator#Efficiency https://en.wikipedia.org/wiki/Radioisotope_thermoelectric_ge...): efficiencies above 10% have never been achieved and most RTGs have efficiencies between 3–7%
jiveWoogie 7y ago
Well, there go my dreams of sunbathing on Mars in nothing but a bikini...
b_tterc_p 7y ago
help me wrap my head around that. If you’re in -40 in a low pressure atmosphere, it doesn’t cool you down faster because there’s less mass for your heat to transfer to? Does that mean things don’t cool down in a vacuum? Is there a weird curve where by at some point having less cold gas arounds you means you’ll cool down faster instead of slower?
- danbruc 7y ago
  Heat transfer happens by heat conduction and heat radiation, so even in a vacuum you will radiate heat away in the form of infrared photons, at least if the vacuum is not at a higher temperature. Heat radiation is however a less efficient process then heat transfer in a sufficiently dense environment. That is also an issue for spacecrafts, they need rather large radiators to radiate away excess heat into space.
  - mytailorisrich 7y ago
    Vacuum does not have a temperature. You would probably need very little thermal insulation, if any, for a space walk around Pluto as heat from sun will be quite low as well.
    - danbruc 7y ago
      If you place a thermometer in space sufficiently far away from all heat sources, it will eventually reach 2.73 K, the temperature of the cosmic microwave background. I am not sure about the correct terminology but at least in some sense this is the temperature of outer space.
      - mytailorisrich 7y ago
        Vacuum has no temperature. What you describe is a black body spectrum 'temperature'.
        danbruc 7y ago
not_a_cop75 7y ago
Those that are used to hiking the Himalayas could live on Mars with a little extra pressurization and some basic filtering. It doesn't seem that unfeasible.

693471 7y ago

Poor understanding of physics are exemplified everywhere these days. It's tiring seeing so many armchair experts trying to take over the discourse with their incessant posturing.

paulcole 7y ago
I'm not sure that's a fair characterization of Elon Musk.
- nolok 7y ago
  Honestly talking about him and his companies is very controversial on HN between the for and against, but I would disagree with you; on almost every PR and marketing pieces and talks he tends to take insane shortcuts.
  - paulcole 7y ago
    > he tends to take insane shortcuts Here on HN we say that is a feature not a bug lol.
nolok 7y ago
Isn't convection against conduction high school level physics though ? I know it was here in France a decade and a half ego when I was there ...
- vonmoltke 7y ago
  Yes, but that assumes most people try to retain that knowledge longer than it takes to pass the final.
  - nolok 7y ago
    Well the details sure, but the general concept ? I have no idea of the basic reproduction number / R0 of any common virus, but I remember the idea of it. Although now that I think of it it's probably a terrible exemple since if people remembered that concept they wouldn't question herd immunity of vaccines. I guess I'm just a bit weirded out.
    - aidenn0 7y ago
      Here's a snippet from a Feynmen talk[1]. He was discussing Latin America, but I think this passage applies equally well to secondary education in the US today: > First, and most serious, I believe, is the almost exclusive teaching and learning by means of pure abject memory. This in no way teaches physics as a science. Nothing is understood; it is only remembered. This in no way satisfies the reasons I outlined for teaching science. Memorization of laws does not permit one to make applications of these laws to new situations; it does not permit one the pleasure of ultimately making scientific contributions; it cannot teach any techniques with the hands. From memorizing, knowledge is not understood, and the beauty of nature is not appreciated. It does not tell how things were found out, or reveal the value of an inventive free mind. > For example, the telescope is an interesting device to make, understand, look through, and play with. It turned men's ideas and minds in new directions. It gave a great impetus to the modern revolution of thought. For a long while it was the sole revealer of the vastness of the heavens and man's modest place in it. But, in Latin America one learns that there are four kinds of telescopes: the Newtonian, the Cassigranian, etc., etc. In the first, the image is virtual and inverted, etc. (I put in all this "etc." because I really don't know how many kinds of telescopes there are, or what their names are, or which way the image is in each kind. But don't underestimate me; I know a very great deal about telescopes – how they work, how to make and use one, their powers and limitations, etc.) The result is that the telescope is lost. There is no more telescope, no lenses, no stars, no eyes, no light – just words memorized without requiring understanding. The examination is passed, for the question was "What are the four types of telescopes?" > I must say immediately that I am not against memorizing. Some things, even many (though nothing special) may be learned by heart; for example, it is good, but not essential, to know by heart 7 x 8 = 56. What I oppose in any teaching philosophy is that the philosophy is used exclusively; but in this case it is especially serious because so little is left of the subject. > ... > When asked what Brewster's Law is, advanced students answer in a flash: "Light impinging on a material of index n is 100 percent polarized with the electric field perpendicular to the plane of incidence if the tangent of the angle of incidence equals the index of refraction." > To these same students I then say, "Look out at the bay from which the sunlight is being reflected. If I look at that reflection through this piece of polaroid and turn it, what will happen?" All I receive are blank stares. No one knows. But I get cries of surprise and delight when they try it and see the reflections getting brighter and dimmer. > This shows something is completely wrong. There is no knowledge whatsoever of nature. With the wrong entrance clue the memorization is useless. These students are like books, no more. I can look in the index of a book under "Brewster's Law" and find a reference equivalent to the students' reply. But in the index I cannot find "sun reflecting on bay." > What do the students know that is not easily and directly available in a book? The things that can be looked up in a book are only a part of knowledge. Who wants such a student to work in a plant when a book requiring no food or maintenance stands day after day always ready to give just as adequate answers? Who wants to be such a student, to have worked so hard, to have missed so much of interest and pleasure, and to be outdone by an inanimate printed list of "laws"? 1: http://calteches.library.caltech.edu/46/2/LatinAmerica.htm http://calteches.library.caltech.edu/46/2/LatinAmerica.htm
DannyB2 7y ago
> Poor understanding of physics are exemplified everywhere these days. Please allow me to quote former vice president Dan Quayle... https://en.wikiquote.org/wiki/Dan_Quayle https://en.wikiquote.org/wiki/Dan_Quayle Mars is essentially in the same orbit. … Mars is somewhat the same distance from the Sun, which is very important. We have seen pictures where there are canals, we believe, and water. If there is water, that means there is oxygen. If oxygen, that means we can breathe.
- not_a_cop75 7y ago
  Oxygen can be harvested from the water, so in that sense he's not wrong. It seems like everyone wants to make every politician into an idiot.
  - antonvs 7y ago
    The Mariner 4 probe showed that there were no canals on Mars, and no open water, by 1965. Quayle's knowledge on the subject was over two decades out of date at the time, and he was supposed to be in charge of the space initiative. Quayle was not a smart man, even by the standards of politicians.

zeristor 7y ago

That’s one of the things I’m curious about regarding the Curiousity rover’s RTG. How efficient is convection cooling in order to maintain the thermal gradient to generate electricity? It has radiator fins, so I assume that’s the main form of cooling over radiation; but with such a thin atmosphere I wouldn’t have that it could take away that much heat.

cbanek 7y ago
Many deep space probes in vacuum have RTG's as well (like Voyager), and they can radiate the heat just fine. Also, over time of course the amount of power and heat they generate lessens.
- jandrese 7y ago
  Isn't the power reduction due to radioactive decay of the fuel? Not that the radiators become less effective over time.
  - cbanek 7y ago
    Yes, but RTGs are not particularly efficient, so much of the energy is heat. From wikipedia (https://en.wikipedia.org/wiki/Radioisotope_thermoelectric_generator#Efficiency https://en.wikipedia.org/wiki/Radioisotope_thermoelectric_ge...): efficiencies above 10% have never been achieved and most RTGs have efficiencies between 3–7%

jiveWoogie 7y ago

Well, there go my dreams of sunbathing on Mars in nothing but a bikini...

b_tterc_p 7y ago

help me wrap my head around that. If you’re in -40 in a low pressure atmosphere, it doesn’t cool you down faster because there’s less mass for your heat to transfer to? Does that mean things don’t cool down in a vacuum? Is there a weird curve where by at some point having less cold gas arounds you means you’ll cool down faster instead of slower?

danbruc 7y ago
Heat transfer happens by heat conduction and heat radiation, so even in a vacuum you will radiate heat away in the form of infrared photons, at least if the vacuum is not at a higher temperature. Heat radiation is however a less efficient process then heat transfer in a sufficiently dense environment. That is also an issue for spacecrafts, they need rather large radiators to radiate away excess heat into space.
- mytailorisrich 7y ago
  Vacuum does not have a temperature. You would probably need very little thermal insulation, if any, for a space walk around Pluto as heat from sun will be quite low as well.
  - danbruc 7y ago
    If you place a thermometer in space sufficiently far away from all heat sources, it will eventually reach 2.73 K, the temperature of the cosmic microwave background. I am not sure about the correct terminology but at least in some sense this is the temperature of outer space.
    - mytailorisrich 7y ago
      Vacuum has no temperature. What you describe is a black body spectrum 'temperature'.
      - danbruc 7y ago

not_a_cop75 7y ago

Those that are used to hiking the Himalayas could live on Mars with a little extra pressurization and some basic filtering. It doesn't seem that unfeasible.