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Scattering of incoming sunlight by the relatively high dust particle content in the Martian atmosphere leads to the sky having significant brightness. The colour of the sky is, in general, reddened with respect to a solar spectrum [Pollack et al., 1977] because, unlike Earth's sky brightness which is dominated by Rayleigh scattering from gas molecules, scattering by dust particles with sizes comparable to or larger than visible wavelengths predominates. This difference has the further significance that while, on a clear day, the blue colour of Earth's sky is rather uniform, the reddening of the Martian sky varies strongly with the angular separation from the Sun. The sky on Mars provides an additional source of illumination to the surface.

The influence of sky colour

We performed a series of observations of the rock, Yogi. 

It was noticed that the colour of Yogi's surfaces changed according to time of day and by looking at the properties of the calibration target, we were able to model the sky brightness and fit the colour changes of the rock.

Relevant Publications:

Markiewicz, W.J., Sablotny, R.M., Keller, H.U., Thomas, N., Titov, D., and Smith, P.H. (1999) Optical properties of the Martian aerosols as derived from Imager for Mars Pathfinder midday sky brightness data. J. Geophys. Res., 104, 9009-9018.

Murchie, S., Thomas, N., Britt, D.T., Herkenhoff, K.E., and Bell III, J.F. (1999) Mars Pathfinder spectral measurements of Phobos and Deimos: Comparison with previous data,  J. Geophys. Res., 104, 9069-9080.

Reid, R.J., Smith, P.H., Thomas, N., Kramm, J.-R., Dummel, A., Crowe, D.G., Lemmon, M.T., Burkland, M., Tanner, R., Johnson, J., Maki, J.N., Gliem, F., Rueffer, P. and Herkenhoff, K.E. (1999) IMP Image Calibration, J. Geophys. Res., 104, 8907-8926.

Smith, P.H., Bell, J.F., Bridges, N.T., Britt, D.T., Gaddis, L., Greeley, R., Keller, H.U., Herkenhoff, K.E., Jaumann, R., Johnson, J.R., Kirk, R.L., Lemmon, M., Maki, J.N., Malin, M.C., Murchie, S.L., Oberst, J., Parker, T.J., Reid, R.J., Sablotny, R., Soderblom, L.A., Stoker, C., Sullivan, R., Thomas, N., Tomasko, M.G., Ward, W., Wegryn, E. (1997) Results from the Mars Pathfinder camera, Science 278 1758-1765.

Thomas, N. Britt, D.T., Herkenhoff, K.E., Murchie, S.L., Keller, H.U., and Smith, P.H. (1998) Observations of Phobos, Deimos, and bright stars with the Imager for Mars Pathfinder. J. Geophys. Res., 104, 9055-9068.

Thomas, N., Markiewicz, W.J., Sablotny, R.M., Wuttke, M.W., Keller, H.U., Johnson, J.R., Reid, R.J., and Smith, P.H. (1999) The color of the Martian sky and its influence on the illumination of the Martian surface. J. Geophys. Res.,  104, 8795-8808.

Thomas, N., Jorda, L., and Markiewicz, W.J., (2000) The effect of diffuse sky brightness on the spectrophotometry of rough Martian surfaces. J. Geophys. Res., 105, 26739-26744.


Space Research & Planetary Sciences Division Web Site