physics says so and the “fault” is its atmosphere

We are increasingly certain that things on Mars are quite different than on Earth. We know that the atmosphere is different, its auroras Y their floors too, but what physics says is that our blue eyes would not be on Mars.

It is something quite curious but that has all the logic, and some of you may already intuit why this would happen. The fact that by going to Mars we would not have seen Matt Damon’s blue eyes as in ‘The Martian’ It depends on the properties of the color itself and the real reason why we see blue eyes, in all their variability. The truth is that it is an eye color that has its trick, as it does not happen with browns, greens and other intermediate tones.

A “fake” eye color

In a strict way, the color of our eyes depends on our genome, our DNA, which determines which proteins we produce and in the end acts as DNI (and a bit of a Family Book, for those who knew him). There is a belief that our color is something of a mixture of our parents, but in reality there are many factors (gene dominance, random iris fissures during fetal development, etc.) that you cannot apply a So easy and straightforward logic.

Speaking of the proteins that we express through our DNA, the one responsible for the color of the eyes is melanin. The amount and distribution of it in our iris conditions the color, hence in the case of humans, babies have blue or gray eyes at birth and over time they can turn brown or another color, as they melanocytes (melanin producing cells, although there are other cells that have pigments in this tissue as we can see in this video about the histology of the iris) develop and synthesize this pigment.

Blue Eyes Cat

Thus, whether we have one color or another depends the amount and type of melanin that occurs in this area: brown eyes have large amounts of melanin, while green and blue have less (especially light tones). But with the blue eyes and her low amount of melanin there is a trick, by the following: if there is no blue pigment or something that gives color to the eyes, why do we see the eyes of blue color?

The capacity of see the colors It exists because it depends on how objects absorb and reflect light, the color that we perceive is the light that comes off them. Light is a wave, therefore each color corresponds to a wavelength and the cells of the retina (the cones) are designed to stimulate themselves and transmit information according to this parameter, so that if an object is blue it is because it has bounced that wavelength to our eyes.

Visible Spectrum
Wavelengths of colors organized in the spectrum of light that we are able to see. Picture: Horst Frank

What do we see, then, in a blue iris? The blue we see is due to tyndall effect, which describes the scattering that occurs when light passes through certain surfaces (a colloidal suspension or the stroma of our eye), producing a blue cloud. The sky is blue because shorter and higher energy wavelengths (speaking of colors, blue and purple) tend to disperse, and although it is not exactly for this effect (now we will remember why), it is very similar.

That is why, as they say in the Fernández-Vega Ophthalmological InstituteSaying that some eyes are “blue like the sky” could not be more correct, since blue is due to similar processes. In this way, the blue color of the iris is due to the fact that without pigments (or with little quantity) waves with shorter wavelength are reflected, that is, blue ones.

Eyes on mars

Seeing that the blue eyes on Earth are, broadly speaking, just as our sky is blue, we have to move to the conditions of the Red Planet. On Mars we saw that their skies are the opposite of those of the Earth: there they have blue sunsets and reddish days, whereas here it is the opposite.

As we explained on that occasion, and how explains NASA very simply, the blue color is due to the scattering of white light from the Sun. On Earth, the atmosphere is relatively dense and the Rayleigh scattering, whereby the short wavelengths (the blue ones) tend to disperse much more than the reddish ones, so that when the Sun is close to the horizon the blue light has already been scattered and that is when we see the orange-red ones.

On Mars there is a much less concentrated atmosphere, Rayleigh scattering occurs to a much lesser extent, and its surface is much drier and more dusty. This atmosphere is usually invaded by numerous fine dust particles, which are closer in size to the wavelength of visible light, and comes into play Mie scattering, which causes long wavelengths (reds) to spread out more evenly.

On Mars, therefore, light in theory has less of a blue component. With less blue component, the “blue” eyes would reflect the other frequencies, which in this case would be the red-orange ones. Hence, if we manage to send an astronaut to Mars and here they have blue eyes, there would be reddish (at least during the day, and not when the reds fade in the afternoon).

In fact, here on Earth it can be represented what would happen on Mars with artificial light (non-solar) without blue component, as explained here by physics Gloria García-Cuadrado on her Twitter account @ciencia__infusa, when talking about this Martian curiosity. Another to add to an eye color that usually draws attention to being a minority, and that curiously persists despite being considered somewhat unadaptive and the fact that all people with blue eyes they seem to have a single common antecedent.


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