Colors -> Mars -> Exobiology -> Homeclick!
Cette page en françaisCliquez!


The colors of the Martian sky - references:

I already explained that I am not at the origin of the idea that the Martian sky is rather blue than red, and that that it has been first explained by Vince Di Pietro, from NASA, from young Ron Levin who saw the first Viking pictures with his father, and that the idea has been later confirmed by people such as John Green of the University of Kentucky.

All I did is try to confirm or deny the idea for my own benefit, and I confirm it. The Martian sky is not this terrible red that is constantly offered to the public. Except during dust storms, the Martian sky is rather blue than red.

Of course, millions of TV viewers have seen this when the first color picture of the Martian surface was broadcasted in 1976. But after 24 years of colorization, who remembers now? Well I do, and other people do.

Here are some references to material of official organizations and/or scientific web sites which you can check for your own information. Please understand that some of these many external links might be broken, sooner or later.

What color should the sky be anyway?

Scientist Dan Shepherd, of the Chemistry and Science Faculty of Bluffton College explains nicely that a red sky is only possible if you have a much denser atmosphere than the Earth has, or an atmosphere tainted by complex molecules such as photochemically generated hydrocarbonates. But we have been told that the Martian atmosphere has less than 1% of the terrestrial atmosphere density, and that there is no organic matter on Mars, allegedly (1).

"To see a red sky all around, one would need either a much thicker atmosphere (in which case it's dubious whether any light would get through at all) or an atmosphere rich in compounds which preferentially absorb blue light. It is actually thought, I believe, that Titan may have a red sky due to the high concentration of more-or-less complex hydrocarbons (photochemically generated) in its atmosphere."

Something to start with. The Martian sky should be blue.

NASA post-colorized Viking images:

At the end of the above linked page you can read the sad reality: the first color picture of the Martian surface, which impressed everyone so much, has been colorized when NASA decided that it did not have the "correct" colors. NASA wanted the sky to appear red not blue, and NASA wanted to get rid of some green patches too.

The second paragraph is amusing: it is told that NASA "understood" that it will be necessary to calibrate "correctly" the cameras before the flights. But this has been done. Viking cameras were calibrated with great care before the flight! We learn that computer software is required to "correct" the colors.

This is exactly what Di Pietro stated. The only missing information in this text is that no mention of the blue color shown in the picture is done. It is just mentioned that the sky had the "wrong" color.

"The Colors of Mars

The first two photos of Mars received on 20 July 1976 were followed by a color photograph on the 21st. A lot of people would not forget that first color picture. Mutch tells the tale as well as anyone. During the first day following the early morning lauding of Viking 1 , his team was preoccupied with analysis and release of those first two images, "which, in quality and content, had greatly exceeded our expectations." So much were they concentrating on the black and white pictures, that they were "dismally," to use Mutch's word, "unprepared to reconstruct and analyze the first color picture." Mutch and his colleagues on the imaging team had been working long hours, along with everyone else, during the search for a landing site. Despite enthusiasm, people were tired. Many of the Viking scientists in the upcoming weeks would have to learn to present instant interpretations of their data for the press. For the first color photograph, haste led to processing the Martian sky the wrong color.
In a general fashion, Mutch and his team understood that a thorough preflight calibration of the camera's sensitivity to the colors of the spectrum was necessary. They also knew that they would need computer software programs to transform the raw data efficiently into an accurate color...

Opinion of the Pathfinder team about Viking images colors:

Here, people at Malin Space Science Systems (MSSS) who are in charge of the recent photographs by Mars Global Surveyor explain that the colors are not very reliable, that the orange on the Martian ground obtained by the Viking colorizers is not geologically correct, too orange, that all the final "improvements" are just hazardous ("more or less an art").

Even better, it is proposed that if the Viking probe appears pink, it is because of dust in the sky. But there was no dust storm at the time when these photographs have been taken. Or if there were, it means that the sky could still be blue when there is no dust storm.

"Viking Lander Color Images

Viking color images of the Martian surface suffer from a variety of uncertainties, in particular the relative brightness of the "red" and "blue" channels. Early reconstructions of the Viking lander images tended to show "blue" sky, while later reconstructions, trying to account for out-of-band contributions in each filter, tended to show a "red" sky, and often an "orange" surface. Owing to calibration uncertainties, the exact reconstruction of Viking Lander color images remains more or less an art. Recognizing that even white portions of the spacecraft will appear slightly pink (or apricot), since sunlight reaching the surface is filtered through the atmosphere, which has a fairly high concentration of dust, and further recognizing that "orange" is not a particularly prevalent geologic "color," the colors in these reproductions tend more towards reddish-browns.

Do not be misled by the politically correct tone which is mandatory here: in plain words, people of Pathfinder are saying that the colorizers of the Viking team are ... artists, because even the Viking probe appears pink orange when it is really white, and that the orange color obtained for the rocks is inappropriate. What is claimed here is that there were "uncertainties of calibration."

As for the out-of-band contributions mentioned here, you will read later in this page that they cannot be accounted for as reason to "correct" the colors, for the simple reason that there were no infra red images available allowing the evaluation of these out-of-band contributions.

NASA explanations:

NASA explains that the Martian sky is yellow-brown, except at dusk and at dawn, when it is pink/red:

"However, further careful analysis of Viking Lander data revealed a Martian sky which is generally "butterscotch" (yellow/brownish) in color, except for the pink/red of sunset and sunrise."

At the bottom of the same page, in total contradiction with the statements at the top, NASA now claims that you get blue colors in the Martien sky only at dusk and dawn, when the oblique rays of the sun are colored by more dust. Do we have to conclude from that, that Martian dust is now blue?

"The blue color only becomes apparent near sunrise and sunset, when the light has to pass through the largest amount of dust."

So, in the same page, because of the dust, the sky is pink-red at sunrise and sunset, then blue at sunrise and sunset. And we get to learn that it would be white if there would be no dust, but that this never occurs. On the photographs shown in the page, it is yellow (Viking), then amber (Pathfinder).

This is highly interesting:

"Pictures from the Hubble Space Telescope in the early 1990s suggested that the Martian atmosphere had much less dust loading than in the Viking years. So perhaps the Martian sky was a different color (i.e. closer to blue) compared to the Viking years. However, this idea is likely incorrect because Mars Pathfinder pictures showed essentially the same sky color and similar dust loading as the Viking landers."

It is very simple. No, the color of the sky does not change when Hubble takes images. The photographs of Hubble were simply true colors, without correction, they show a blue sky, and it would be the same for both Viking and Pathfinder ground images if they had not been tampered with. It is notable that the Pathfinder pictures are less and better colorized than those of the Viking pictures, the Pathfinder team is careful not to colorize the Viking lander is an exaggerated and telling manner...

JPL explains:

People at JPL explain that the pink sky is the correct color, for there is dust. Question: when the dust storm is over, what is the correct color then?

"Scientists believe the colors of the Martian surface and sky in this photo represent their true colors. Fine particles of red dust have settled on spacecraft surfaces. The salmon color of the sky is caused by dust particles suspended in the atmosphere."

They try to make us believe that the pretty colors of the Viking lander are not an effect of the coloring of the photograph but is caused by dust deposits on the normally white surfaces of the machine. But then, why are these surfaces are yellow on the first photograph, then, depending on which photograph you choose, pinks, lilac, amber, salmon, yellow, and even again, white?

Here is a web page from JPL showing splendid photographs. What happens to the colors? At the bottom of the page the explanation is that they are adjusted to look "Martian." The software is Photoshop, seemingly.

"The color balance was adjusted to approximate the true color of Mars." Did they forget Viking team told that the calibration had to be done in advance, not once on Mars? Why would they change the colors once there?

Hubble team heats up the debate:

Here a communication by Hubble Space Telescope Team announcing that if there is no storm, the sky is blue (extracted):

Don Savage
Headquarters, Washington, DC July 1, 1997
(Phone: 202/358-1547)

Tammy Jones
Goddard Space Flight Center, Greenbelt, MD
(Phone: 301/286-5566)

Ray Villard
Space Telescope Science Institute, Baltimore, MD
(Phone: 410/338-4514)

RELEASE: 97-148

(...) "If dust diffuses to the landing site, the sky could turn out to be pink like that seen by Viking," says Philip James of the University of Toledo. "Otherwise, Pathfinder will likely show blue sky with bright clouds." (...)

It seems that there is not ALWAYS dust in the air, after all. And if there is no dust the sky would be blue indeed blue, as any scientist would know.

In fact the true colors photographs by Hubble showed a quite blue atmosphere around of Mars, definitely visible on the periphery of planet:

Here is one of the rare photographs on which Hubble people did not remove the blue atmosphere. On all the latest Hubble photographs, the Martian atmosphere has been cropped out so that no blue is shown anymore. Note that the high version picture is not there anymore. You will find these images in my site. I did take the precaution to copy them. Anyway, even on the low resolution version which is left here, if you save it on your hard disk and zoom it, you will be able to see the blue atmosphere:

Mars before

This is what is left of the atmosphere since Hubble people noticed that they awkwardly refuelled the controversies. This image is on, you will note that Mars has no atmosphere now. It has been confiscated.

Mars after

Another surviving image showing the blue atmosphere; it was a little difficult to find as it was saved on a temporary web folder of the Hubble Mars web site. Enlarge it.

Now, just try to find one photograph by Hubble on the official site showing a red or pink athmosphère. Good luck...

Of course, elsewhere, in the press, other sites, like the CNES site (CNES is the French NASA equivalent), you will find heaps of very red photographs. The red Of shame?

The Hubble guys, once they understood that it is not welcome to criticize the "red sky" concept, the official party line, start to "correct" the colors of Mars too:

"LEFT This "true-color" image of Mars shows the planet as it would look to human eyes. It is clearly more earth-toned than usually depicted in other astronomical images, including earlier Hubble pictures."

A picture by the Lovell telescope, 1988:

When asked, NASA scientists say the Martian sky should be blue:

Check on please, if this is correctly reproduced:

NASA people explain that the sky could be a quite blue after all:

If the winds of Mars were completely calm, so that no dust particles were stirring, what color would the Martian sky have at midday and at dusk? Does this ever happen?

ANSWER from Mary Urquhart on July 14, 1997:
A good question. You are perfectly correct in thinking that an absence of dust will change the color of the Martian sky. Without any dust in the atmosphere the sky would probably be a dark blue at midday (darker than the Earth's sky because the atmosphere is much less dense and so there are fewer air molecules to scatter blue light. At dusk the sky would probably have a slight reddish hue in the west, particularly if the Martian clouds were reflecting sunlight. The reason for the reddish color would be the same as on the Earth. Gas molecules scatter blue light and when you look at the Sun at sunset you are looking through more gas because the Sun is closer to the horizon. With the blue light scattered out, the remaining light is reddens. Once again, this effect will be slight compared with the Earth because there is less gas in the atmosphere of Mars.

Mary Urquhart
Laboratory for Atmospheric and Space Physics
University of Colorado at Boulder

ANSWER from Jim Murphy on July 15, 1997:
This is a great question about Martian sky color and suspended dust, and we here on the Pathfinder meteorology team have spent quite a bit of time talking about it. If the Martian atmosphere were completely clear of dust, I think that the sky would be quite a bit darker than clear skies here on earth. If you have ever flown on a plane at 30,000-35000 feet during daytime, and looked at the sky, you might have noticed that it appears much darker than from the surface, especially when you look at particular angles away from the sun. This darker appearance is due in part to the reduced scattering the light experiences at these high altitudes (low air on the surface of mars!!) compared with the much greater numbers of molecules the sunlight can 'bump' into on its way to the surface. Blue light is scattered more effectively by molecules than is the longer wavelength red light, which is why the sky looks blue.

I don't expect that the Martian atmosphere will clear substantially during Pathfinder's mission on the surface. In fact, I expect the atmospheric dust content to increase as summer gives way to autumn. But, if the atmosphere were to clear (I've blown forecasts before :-) ), the sky would be bluer, but not the light blue that we see on a terrific day here on Earth. It would be a beautiful picture of Mars, however.

Thanks for the question.

Jim Murphy
Mars Pathfinder ASI/MET Science Team

All the colors of a rainbow:

Let us check now with which highly scientific precision the "corrections" to obtain "the true" colors of Mars are applied by NASA:

Underneath are sa small set of Mars pictures from NASA sites and NASA contractors sites showing the surface of Mars. Believe me or not, I did not have the chance to tamper their images on their sites!

A green sky:

NASA comments: "Using the computer, those colors are then painted onto high resolution images covering the same area. The image has had its colors balanced to approximate what a person would see on Mars. Since the Martian atmosphere carries extremely fine-grained red dust in suspension the "on Mars" images are redder."

A white sky:

A yellow sky. You can zoom on the red colored cables if you want to check the Photoshop work.

Comment: "Ordinarily images are redder, since the Martian atmosphere carries extremely fine-grained red dust in suspension."

An almost blue sky:

So, in the name of scientific realism, colored the sky sometimes in white, green, yellow, then in gray-pink-blue, explaining that it is red because of dust, telling us that it is blue dark if there is no dust, and by considering apparently that all the photographs are taken in dusty weather.

Here a yellow sky. Apparently, the Viking lander was yellow, and not white, as one would have thought. This is what NASA calls "recalibration" to show the true colors of the Viking lander.

Sky turns red again:

The US flag was thought to be red blue and white. Not at all! The new colors are purple yellow and red.

At this address, you can find the composites of the first image color by Viking, with all the data about the filters and adjustments used:

Here you will find the color reference palette which has been gauged on Earth before the mission. When the color image was recomposed, it showed a blue sky. Only then, NASA people decided to change the adjustments to show a pink, yellow or red sky.

All the raw data and technical information is on a University site which now contains all the raw images of the Viking mission.

NASA's JPL has this nice picture:

Once in a while our friends forget to colorize...

But they did not miss that one: (as the filename indicates?):

A nice pinkish hue:

Check here the authenticity of this image:

NASA historical website:


NASA is totally uncertain. There were no infra-red reference image, so they could not really take the out-of band amounts of light for each filter into account. It would have been too simple to just use the correct precalibrated color balance which was carefully gauged on Earth, right?.

Because there was no accompanying IR image, it is not possible to compensate for irregularities in the camera color filters.

Of course, when there is too much red, the blue of the reference color pallet appears purple, a child would know this:

Difficulties in precisely balancing the colors are indicated by the violet hue of the blue color chip on the test chart.

Well, use your Photoshop or Paint Shop Pro of whatever, and get this purple horror back to blue...



I gathered the above in 2001, it did not require revision since.

However, in 2004, I had the opportunity to check more aspects of that question, which reinforced the opinions presented here.

Valid XHTML 1.0 Strict

 Feedback  |  Top  |  Back  |  Forward  |  Map  |  List |  Home
This page was last updated on October 19, 2001.