Temperature of phobos in the daytime?

Answer 1

By direct measurement by NASA spacecraft, maximum temperature on the sunlit side of Phobos was measured about 269K = -4 C = 25 F, given on nasa website. This is somewhat different than doing a radiative equilibrium calculation by theory, equating the power absorbed

Luminosity_sun * radius^2 * (1 - Albedo) / (4 * Distance)^2

to the power radiated

4 * pi * radius^2 * StefanBoltzmannConst * Temp^4

and solves for temperature

Temp = (L_sun * (1 - Albedo) / (16 * pi * SBC * Dist^2))^0.25

= {3.85E26[W] (1 - 0.07) / (16 * pi * 5.67E-8[W/m^2/K^4] * D^2)}^(1/4)

Where distance D, in meters is 1.52 [AU] * 1.49E11 [m/AU]

rendering a temperature of 222K = -60 deg F . One may consider

(mars) distance at aphelion of 1.66 AU for low sun-side temp 212K = -78 F

or use, for high sunlit temp, the perihelion dist 1.38 AU for T = 233K = -40 F, given by wikipedia The reason the measured high temperatures are greater than the calculated temps [other than also subtracting the phobos - mars (thought here to be negligible) radius from the sun - mars distance for minimum phobos - sun distance] is that there is some reflected light from the surface of phobos illuminating a temperature probe, possibly some light from mars and starlight. There also may be some plasmas present from the solar wind boosting the temperature slightly.

Answer 2

The temperature is about -4C (25F) on the sunlit side.