Wayne Warren wrote:
Red sunsets on Earth are a result of blue light being scattered away by the atmosphere. Mars' atmosphere is much less dense, so more blue light gets through and the Sun looks bluer. Scattering is proportional to the inverse fourth power of the wavelength. The properties of the Martian atmosphere must have an effect too.
Red skies and blue sunsets on Mars are the result of
red light being scattered by moderately large red dust particles.
Dust scattering is proportional to the inverse fourth power of the wavelengthonly
for infrared wavelengths much longer than the dust particle size of ~3 µm in diameter.
http://en.wikipedia.org/wiki/Martian_so ... heric_dust wrote:
<<Mars is covered with vast expanses of sand and dust and its surface is littered with rocks and boulders. The dust is occasionally picked up in vast planet-wide dust storms. Mars dust is very fine and enough remains suspended in the atmosphere to give the sky a reddish hue. The reddish hue is due to rusting iron minerals presumably formed a few billion years ago when Mars was warm and wet, but now that Mars is cold and dry, modern rusting may be due to a superoxide that forms on minerals exposed to ultraviolet rays in sunlight.
The Martian atmospheric dust particles are generally 3 µm in diameter. It is important to note that while the atmosphere of Mars is thinner, Mars also has a lower gravitational acceleration, so the size of particles that will remain in suspension cannot be estimated with atmospheric thickness alone. Electrostatic and van der Waals forces acting among fine particles introduce additional complexities to calculations. Rigorous modeling of all relevant variables suggests that 3 µm diameter particles can remain in suspension indefinitely at most wind speeds, while particles as large as 20 µm diameter can enter suspension from rest at surface wind turbulence as low as 2 ms−1 or remain in suspension at 0.8 ms−1.>>