Surface Temperature of the Moon and Mars

The moon is quite a bit warmer than Mars, but Luna has greater temperature extremes. Over the period of a day, Luna's surface temperature gets much warmer and much colder than Mars.

A habitat on the surface of either Luna or Mars will need some kind of thermal capacitor to smooth out the temperature swings, but this would be a greater challenge on the moon because of the length of its day and the wide variation in temperature.

On the other hand, due to the bitterly cold temperatures of Mars, a habitat on the surface of Mars would require quite a bit of power for heaters and probably exotic materials for any equipment used outside. This is less of a problem on Luna because metals will have a chance to warm up each day, but at the cost of strain hardening (due to thermal cycling) if they aren't insulated. Fortunately, when the average temperature is workable, insulation is relatively easy.

Lunar temperatures vary throughout the month-long lunar day, but the lunar year doesn't experience much seasonal variation. Martian temperatures vary wildly in both a diurnal cycle and a lunar cycle.

We can expect that on the moon, people will conduct most of their surface activities in the balmy mornings and afternoons (each of which is an Earth week long), and put the equipment in garages at noon and midnight. They should be able to work outside even at lunar noon if they have a sunshade. (A parasol of thin aluminum foil would do nicely for this.)

On Mars, people will scramble about in arctic conditions for a few hours each day during the summer, and then spend the next year and half (Earth time) working indoors. This is why terraforming Mars is such an attractive subject; we need to warm up the red planet to make it really useful. Time estimates for how long it will take to warm the planet vary between 500 and 50,000 years, so this is a very long-term project in any case.

That's for the surface. A habitat less than a meter beneath the surface of Luna will experience a very constant temperature equal to its mean surface temperature. That's about -9°F (-23°C). The lunar regolith is such a good insulator that the habitat will need a heat-rejection system even at night because of the heat given off by equipment and inhabitants of the lunar habitat.

For Mars, a subsurface habitat will need a power supply to keep it warm. A nice radioisotope thermal generator (RTG) sounds like the best solution to me. Maybe we'll get lucky and find some fissible material on Mars.

Temperature Data

If you survey the web for temperature data, you'll find dramatic variations in the numbers quoted, even among web sites that are copying each other. There's also little consistency, even within a given web site, in which temperature scale is quoted. One of the most frequent errors is to specify the wrong temperature scale, substituting Centigrade for degrees Fahrenheit; and even more often substituting Kelvin for Centigrade.

So, after digging through that mess, I went back to half a dozen books in my study to check references found on the web, and came up with what I think are the most consistent and believable numbers for the mean, maximum, and minimum surface temperatures. The table below quotes these temperatures in Fahrenheit, Rankine, Centigrade, and Kelvin. (Rankine and Kelvin are absolute scales. At 0°R or 0°K, nothing moves.)

     Mean Surface Temperature

                          F      R      C      K
          Earth          59    519     15    288
          Moon           -9    451    -23    250
          Mars          -76    384    -60    213

     Minimum Surface Temperature

                          F      R      C      K
          Earth        -128    332    -89    184
          Moon         -233    227   -147    126
          Mars         -170    290   -112    161

     Maximum Surface Temperature

                          F      R      C      K
          Earth         136    596     58    331
          Moon          212    672    100    373
          Mars           17    477     -8    265

If you want to work temperature comparisons in your own machine, you might want to look at the functions I used in my attempt to restore some order from the chaos:

            ftoc = (degf - 32) * (5 / 9)
            ctof = (9 / 5) * degc + 32
            ftor = degf + 459.7
            rtof = degr - 459.7
            ctok = degc + 273.16
            ktoc = degk - 273.16
            ktor = degk * 9 / 5
            rtok = degr * 5 / 9
            ktof = ctof(ktoc(degk))

Also see: Temperatures on the Lunar Surface in Appendix M.