sysD Posted March 30, 2011 Share Posted March 30, 2011 NASA now has a satellite orbiting Mercury and snapping photos. http://blog.seattlepi.com/aerospace/2011/03/29/heres-mercury/ http://www.latimes.com/news/science/la-sci-messenger-20110330,0,7061787.story The second article is from the LA Times. It states that NASA's photos capture "areas near the planet's southern pole that have never been seen before — areas that could host water in the form of ice." How is this even possible? The surface temperature of Mercury would instantly evaporate any form of water, without even taking into account the amount of pressure that close to the sun. Link to comment Share on other sites More sharing options...
Spyman Posted March 30, 2011 Share Posted March 30, 2011 (edited) From your own link: "Even though Mercury sits blisteringly close to the sun, some areas in craters near its poles lie in permanent shadow — and are probably cold enough to house ice deposits." From Wikipedia: "Mercury is similar in appearance to the Moon: it is heavily cratered with regions of smooth plains, has no natural satellites and no substantial atmosphere." "Surface temperatures range from about 90 to 700 K (−183 °C to 427 °C), with the subsolar point being the hottest and the bottoms of craters near the poles being the coldest." "The mean surface temperature of Mercury is 442.5 K, but it ranges from 100 K to 700 K due to the absence of an atmosphere and a steep temperature gradient between the equator and the poles. The subsolar point reaches about 700 K during perihelion then drops to 550 K at aphelion. On the dark side of the planet, temperatures average 110 K. The intensity of sunlight on Mercury’s surface ranges between 4.59 and 10.61 times the solar constant (1,370 W·m−2). Although the temperature at the surface of Mercury is generally extremely high, observations strongly suggest that ice exists on Mercury. The floors of deep craters at the poles are never exposed to direct sunlight, and temperatures there remain below 102 K; far lower than the global average. Water ice strongly reflects radar, and observations by the 70 m Goldstone telescope and the VLA in the early 1990s revealed that there are patches of very high radar reflection near the poles. While ice is not the only possible cause of these reflective regions, astronomers believe it is the most likely. The icy regions are believed to contain about 1014–1015 kg of ice, and may be covered by a layer of regolith that inhibits sublimation. By comparison, the Antarctic ice sheet on Earth has a mass of about 4×1018 kg, and Mars' south polar cap contains about 1016 kg of water. The origin of the ice on Mercury is not yet known, but the two most likely sources are from outgassing of water from the planet’s interior or deposition by impacts of comets." Wikipedia Link to Mercury Why do you think there is higher pressure "that close to the sun" ? Mercury is orbiting the Sun in nearly empty space just like Earth or the other planets in our system. Edited March 30, 2011 by Spyman 1 Link to comment Share on other sites More sharing options...
lemur Posted March 30, 2011 Share Posted March 30, 2011 (edited) Doesn't the planetary mass conduct heat from the hot side to everywhere else? If not, it's interesting to imagine what could be possible in terms of solar-energy uses, if there's any use for solar energy on Mercury that is. Edited March 30, 2011 by lemur Link to comment Share on other sites More sharing options...
CaptainPanic Posted March 30, 2011 Share Posted March 30, 2011 Doesn't the planetary mass conduct heat from the hot side to everywhere else? If not, it's interesting to imagine what could be possible in terms of solar-energy uses, if there's any use for solar energy on Mercury that is. It's in fact the atmospheres that transport heat the most efficiently from hot to cold. (Convection almost always beats diffusion). Link to comment Share on other sites More sharing options...
lemur Posted March 30, 2011 Share Posted March 30, 2011 (edited) It's in fact the atmospheres that transport heat the most efficiently from hot to cold. (Convection almost always beats diffusion). If Mercury were made of iron, I would find it hard to believe that 400C on one side would be insulated from the -100C on the other side. What prevents that heat from conducting through the interior? It's not like the energy can radiate away on the sunny side. Edited March 30, 2011 by lemur Link to comment Share on other sites More sharing options...
imatfaal Posted March 30, 2011 Share Posted March 30, 2011 If Mercury were made of iron, I would find it hard to believe that 400C on one side would be insulated from the -100C on the other side. What prevents that heat from conducting through the interior? It's not like the energy can radiate away on the sunny side. Well the dark side clearly does get heated by the light side as the darkside has a temperature of 100K - which is considerably higher than the space that surrounds it. It is clearly wrong to suggest that the sunnyside would be the same temperature as the darkside - and it seems that the equilibrium is that the side with no sunlight gets to around 100k before its emission balance out the conducted heat from the sunnyside Link to comment Share on other sites More sharing options...
Airbrush Posted March 30, 2011 Share Posted March 30, 2011 One day on Mercury is equal to 176 Earth days. 1 Link to comment Share on other sites More sharing options...
sysD Posted March 30, 2011 Author Share Posted March 30, 2011 Why do you think there is higher pressure "that close to the sun" ? Mercury is orbiting the Sun in nearly empty space just like Earth or the other planets in our system. I figured that the intense heat that close to the sun = more excited particles; therefore higher pressure. However, I forgot to take into account that Mercury has a virtually non-existent atmosphere, and pressure requires a medium to pressurize =p Link to comment Share on other sites More sharing options...
SMF Posted March 30, 2011 Share Posted March 30, 2011 Airbrush provided the solar day length, while Mercury's sidereal day is 58 days, 15 hours. Earth's sidereal day is only four minutes shorter than its solar day. SM Link to comment Share on other sites More sharing options...
insane_alien Posted March 30, 2011 Share Posted March 30, 2011 even if mercury was made of diamond(the most heat conductive substance known) the dark side would still be cold. it is not enough for there to be only conductive material, there must be a short enough distance so as to allow a high heat transfer. copper is electrically conductive, but just go and see how much juice you can put through a 6000 mile cable with a 1.5V battery. 1 Link to comment Share on other sites More sharing options...
jamiestem Posted March 30, 2011 Share Posted March 30, 2011 Exactly. It may be small, but it's huge ya know! Conducting heat through such a long distance isn't going to happen, as stated above. Is Mercurys core known to be iron? or just directly below the surface? If not, What is the core of Mercury made of? And is it cold inside as suggested or could that be wrong now too? Link to comment Share on other sites More sharing options...
lemur Posted March 30, 2011 Share Posted March 30, 2011 even if mercury was made of diamond(the most heat conductive substance known) the dark side would still be cold. it is not enough for there to be only conductive material, there must be a short enough distance so as to allow a high heat transfer. copper is electrically conductive, but just go and see how much juice you can put through a 6000 mile cable with a 1.5V battery. Exactly. It may be small, but it's huge ya know! Conducting heat through such a long distance isn't going to happen, as stated above. Is Mercurys core known to be iron? or just directly below the surface? If not, What is the core of Mercury made of? And is it cold inside as suggested or could that be wrong now too? I guess as strong as the radiation is on the sunny side, it still isn't enough to make up for the heat-drain of the radiating dark side. I wonder what the gradation of temperature from the hot side to the cool side would be like if you could take samples tunneling through the center. Link to comment Share on other sites More sharing options...
insane_alien Posted March 30, 2011 Share Posted March 30, 2011 well, mercury will still have some primordial heat and will be heated internally from radioactive decay so it'll look much like a cross section of earth but wit ha greater difference in temperatures at the extremes. below a kilometer it would be impossible to tell whether it was day or night. probably a good deal closer to the surface in fact but i can't be bothered running the calculations. Link to comment Share on other sites More sharing options...
lemur Posted March 30, 2011 Share Posted March 30, 2011 well, mercury will still have some primordial heat and will be heated internally from radioactive decay so it'll look much like a cross section of earth but wit ha greater difference in temperatures at the extremes. below a kilometer it would be impossible to tell whether it was day or night. probably a good deal closer to the surface in fact but i can't be bothered running the calculations. Do you know what the wattage per square meter on the sunny side is from solar radiation, by chance? I'd just like to get an idea of how much energy is hitting it. Link to comment Share on other sites More sharing options...
insane_alien Posted March 30, 2011 Share Posted March 30, 2011 ~9.31kW/m^2 depends on where mercury is in its orbit though. 1 Link to comment Share on other sites More sharing options...
lemur Posted March 30, 2011 Share Posted March 30, 2011 ~9.31kW/m^2 depends on where mercury is in its orbit though. Oh. I guess that's only about 10X solar power on Earth, but without an atmosphere to cool it, I guess the heat has to conduct its way through to an area of the surface that's not facing the sun in order to radiate away into space. Link to comment Share on other sites More sharing options...
insane_alien Posted March 30, 2011 Share Posted March 30, 2011 no, the surface facing the sun will radiate as well. the surface during the day will be at radiative equilibrium (minus a bit thats conducting into the plane which comes back out at night.) this can happen because even on mercury, most of the sky isn't sun and thats good enough for radiative cooling. Link to comment Share on other sites More sharing options...
lemur Posted March 30, 2011 Share Posted March 30, 2011 no, the surface facing the sun will radiate as well. the surface during the day will be at radiative equilibrium (minus a bit thats conducting into the plane which comes back out at night.) this can happen because even on mercury, most of the sky isn't sun and thats good enough for radiative cooling. I guess I sort of assumed that the sun was most of the sky, or a large portion of it anyway. If it isn't, then what you said makes sense. Good point. Link to comment Share on other sites More sharing options...
CaptainPanic Posted March 31, 2011 Share Posted March 31, 2011 What prevents that heat from conducting through the interior? It's not like the energy can radiate away on the sunny side. Heat is indeed being conducted. You just overestimate how much energy can be transported that way. Heat transport increases with an increase in temperature difference between hot and cold. But it decreases with increasing distance between the hot and cold locations. And on a planet, that distance is the problem. Convection and radiation can transport energy across a distance much better than heat conduction through a material. That's why your central heating system transports water through a pipe to a radiator rather than just have a big iron cylinder in the house. And yes, energy can in fact radiate away on the sunny side. In fact, probably most energy is being radiated away directly from the sunny side, straight into space. Link to comment Share on other sites More sharing options...
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