Thursday, 19 January 2017
The Martian Sky Revisited - Orange Earth Sunsets, Blue Mars Sky, and Dust
To understand the argument put forward about Mars having a Blue Sky, and therefore a thicker atmosphere than NASA or the ESA has claimed, we need to understand how the colouring of the sky on Earth works:
The colours of the sky on Earth are a function of our relatively thick atmosphere. Our blue skies occur due to the scattering of the blue wavelength of light from white light coming from our star.
The sky looks orange when the Sun appears at a low angle in the sky because the light travels though more atmosphere and the blue wavelength has been scattered away leaving the longer red wavelength.
Dust in the atmosphere also contributes to the sunset colours. The clouds and other aerosols reflect these colours.
If we believe NASA the atmosphere on Mars is as thin as on Earth at 100,000 feet. From near 70,000 feet and above the sky directly above on the daylight side of Earth is black.
To have a red sky would require a lot of obstruction (dust or gas) to block out or scatter the blue wavelengths. According to NASA the red sky cannot be due to gas.
The problem is that we consistently get orbital pictures of Mars that does not show any of the dust haze that would be needed to get the consistent orange-red skies NASA shows. On Earth, if you get orange daytime skies it is in conditions of a dust storm. The clear orbital pics should mean we see black skies, like on Earth at high altitude. Either the orbital pictures are in error or NASA's red sky pictures are not true colour representations.
In fact early pictures from Viking and even some pictures from the current set of landers/rovers show blue skies. This is indicative of a thicker atmosphere. It also would account for surface features that look like water run off channels - near impossible in a super thin atmosphere, but easily explained if the atmosphere was slightly thicker (like on Earth at 29,000 feet - the top of Mount Everest).
The argument being made here is from basic scientific principles and observations.
To get the red skies NASA shows on Mars you need a LOT of dust. The fact that we often have clear skies (no haze) and no black sky pictures, and the fact that we sometimes see blue skies is indicative of NASA portraying Mars with false colour imagery.
If blue is eliminated from the colour pictures then you get lighter surface details. The problem is you also end up with false colour (red) images of the sky.
We even have NASA pictures that show the elimination of blue from the colour composition. In this picture from the Spirit rover mission you can see the colour calibration sundial and blue strips that come up pink:
Blue has been removed from the image. If blue is added back in, and we end up with a blue sky, then Mars has a thicker atmosphere than we've been led to believe.
[Posted at the SpookyWeather blog, January 19th, 2017.]