Celestia Forums

Hi all,

since my early contributions to Celestia, I was always concerned with trying
to get things as close as possible to reality;-)...The true color
of Mars is one such issue that has puzzled me for quite a while.

After all that extensive texture work, I don't want it to be too far off...

So I did some fairly thorough research on this, and now I believe that I found
the right answer, at last! Thanks also to Jack Higgins, who pointed me
onto the right track a few days ago!

Here comes my little story:

For the Mars oppositions between 1995 and 2003, we have continuous,
high quality tricolor (RGB) imaging from HST's wide field camera. In view of the excellent color rendition of other planets by that HST camera over the last decade, I was always tempted to believe Hubble's reddish Mars color. Notably, since the earlier Mars missions were mainly restricted to two channel color imaging!

As an illustration of the great 'red color consistency', I have started off to
assemble a composite image of the official HST images from
Mars' oppositions in 1995, 1997 and 1999, below. I have only adjusted
slightly the brightness of these images to demonstrate clearly
that throughout these years, the HST Mars colors are perfectly
consistent and definitely redish orange.

So far so good, but here is the puzzle:

An amazing and systematic change of Mars' HST color rendition
happened somewhen around 2000, as you can see further below from the
excellent HST images of 2001 and this year's great opposition!!

Mars has now been definitely 'declared' yellowish brown!

What happended? Have a look first:

1995 - 1999 ==> only red Mars oppositions! Note also the clear and
persistent blue hue of the atmosphere....



The point is that the Mars Pathfinder mission has
apparently provided most credible new spectroscopic information both
of the sky color and that of the Mars surface!. This
new information was processed and published around 1999 and meant the
end of the red Mars;-)...

The most important scientific papers on this controversial matter are
these two that I have consulted also:

J.N. Maki et al., 'The Color of Mars: Spectrophotometric measurements
at the Pathfinder landing site', J Geophys Res 104, 8781 (1999)

N. Thomas et al., J Geophys Res 104, 8795 (1999)

The "Imager for Mars Pathfinder" (IMP) is a stereo imaging system that, in
its fully deployed configuration, stands 1.8 meters above the Martian
surface, and has color capability provided by 24 selectable filters --
twelve filters per 'eye'. Its red, green, and blue filters were used
to take the panorama at the top of my second image below.

The three color images were first digitally balanced according to the
transmittance capabilities of a specific high-definition TV device at
JPL, and then enhanced via changes to saturation and intensity while
retaining the hue. A threshold was applied to avoid changes to the
sky.

Maki et al., (1999) found that the IMP was stable during the mission
and were therefore able to confidently calculate the true color of the
Martian sky and surface by relying on the absolute calibration of the
IMP. Specifically, the authors categorically assert that,
notwithstanding the fact that Mars has historically been referred to
as the "Red Planet", the true color of the surface matches that of the
sky - yellowish brown, with differences attributed to brightness
levels. Moreover, although the surface color is not time dependent,
the sky color becomes red in the anti-Sun direction and is reddest at
noon. Blue, just enough to be scientifically measurable and only
present in enhanced imagery, becomes apparent only toward the Sun at
sunrise and sunset.

Moreover, Thomas et al., (1999) agreed with Maki et al., (1999) that
the reddening of the Martian sky, unlike Earth's blue sky color, is
highly variable and directly related to the angular separation from
the Sun.

So have a look at my next composite image, that again demonstrates the
overall consistency in the new 'official' True Mars color after
Pathfinder!. Again the blue hue of the atmosphere is clearly
visible.

Altogether, I am now convinced that the color below is the closest
approximation todate of the true color of Mars!;-):



Finally, a most revealing comparison of the sky color measurements from
Pathfinder with Celestia's present colors. There is definitely still some fine
tuning to be done, although the brown-bluish sky at sunset is very nice
already!

Bye Fridger

well, it seems that someone has been working here...
good job Fridger!!!


bte: i always thought: why one of the probes sent to mars can't carry a simple camera, like the ones we use here on earth? won't the pictures have the right colors???

Well done Fridger!

ElPelado wrote:bte: i always thought: why one of the probes sent to mars can't carry a simple camera, like the ones we use here on earth? won't the pictures have the right colors???

It's because they want their cameras to take pictures at different wavelengths, to bring out detail on rocks like composition etc, which you can tell through IR/UV & not visible light.

Light isn't just "colours" really, it's different wavelengths! We see colour as RGB because we have sensons on our retinas (ath the back of your eye) which sense for these 3 wavelengths, and the brain percieves them as red blue & green!

Jack, i mean that the rovers or what ever we send to mars, can carry a normal camera TOGETHER with the cammeras that they need to make studies. not just a normal cammera

ElPelado,

The problem is "what do you mean by normal camera?"

One of the problems is that the light illuminating the surface of Mars, for example, has been distorted by passage through the Martian atmosphere and the dust that's in it. The light getting through to the surface of the Earth is distorted in different ways by the Earth's atmosphere and the water, dust and pollen that's in it. Different wavelengths get through to the surface in slightly different proportions. This changes the apparent color of objects.

The TV cameras used in studios require special lighting: very bright and very blue. When you're inside your home, the room lights are rather red if you have incandescent (filament) light bulbs. If you have fluorescent lights, the lighting is usually quite blue. The human eye and brain automatically compensate. Most consumer video cameras have been designed to automatically hide this lighting effect from you by generating colors that look "right".

Photographers who use film always have to adjust for these kinds of effects. Different films have different color responses. If you use a film designed for inside use (with incandescent lights), you have to put a reddish filter on the camera lens if you use that film to take pictures outside. Daylight is very blue.

After many years of study, we know exactly what is different among the kinds of lighting we have on the surface of Earth. We are still arguing over what the differences are in the lighting on the surface of Mars.

Scientific cameras don't make any automatic adjustments for color balance. They must not hide the different light levels. A consumer camera would be very confused by color of the Martian daylight.

Does this help clarify things a little?

yes it does selden. i haven't tought about it. now i understand all the problems with mars' colors.
thanks.

Hi Fridger,

Here is also a good site about this topic.
http://www.donaldedavis.com/PARTS/MARSCLRS.html
http://www.donaldedavis.com/PARTS/MARSCLR2.html

Bye Jens

jim wrote:Hi Fridger,

Here is also a good site about this topic.
http://www.donaldedavis.com/PARTS/MARSCLRS.html
http://www.donaldedavis.com/PARTS/MARSCLR2.html

Bye Jens

Jens,

honestly, I am not so fond about these articles. They certainly cover the same topic. However, the strategy underlying the author's various color modifications of the published results is not at all transparent to me. Sure, there are lots of image manipulation experiments on display. Yet, he does not distinguish at all clearly what is known for sure, what is speculation and what is his artist phantasy....Also the conclusions remain open...

The pictures look admittedly good, though. Was it that what you liked most?

Bye Fridger

Hi Fridger,

sure this articel is not really scientific accurate and detailed but it's worth to have a look at it. I think the colours are not complete wrong and somethings sounds very plausible. So far it was the best information I found on the net. Generally I think it's hard to find infos about the real colours (or what a astronaut would see) of any celestial bodies. For example all the colour pictures of the Voyager missions have to much red. Io looks in reality dirty yellow-green-grey and not orange.
http://www.lpi.usra.edu/research/outerp/io-nat.gif

Bye Jens

Fridger et al,

Sorry to bring this up again after a few weeks (thats what one gets for moving office and being on vacation ).

You are right in noting that there has been a color shift in posted images. Unfortualtely, NASA is notorious for procesing images to make them look the most spectacular, not the most true to life. I have always been very critical of colors as seen in images, particularly of fainter fuzzies.

I can shed a little light on this subject through a very fortunate turn of events that resulted in my getting to look at Mars (and Uranus) through the 3.5m telescope at Apache Point Observatory the other night.

The big trick to being able to properly percieve color through a telescope comes down to aperture. With that much light gathering power, I believe that the color rendition on these fairly bright objects was as good as one can get it.

Of course, there is always a personal equation when it comes to percieving color, and it is likely that no two people will see the same color when looking at the same object. That said, I see the color of Mars as even LESS orange than the most recently posted HST images. It is close, but to my eye, it just doesn't look right. I see it as more to the yellow/beige than anything else. Remember that Martian soil is a mix of sand (like what we have here in the deserts of the southwestern US) and iron oxide as a first approximation. Take the two an mix together and you get a feel for what it is like.

Of course, the real answer can be best found by looking a a vial of Martian Soil Simulant produced by the Jet Propulsion Lab several years back. It is pulverized lava rock from Hawaii that has been procesed in such a way to match the spectral signature of Mars as close as possible (in other words the same color in all wavelengths). I have to dig up the small sample I have and take a closer look, but as I recall from that, my assertion that Mars is more yellow than orange is close.

Just my two cents worth. Hope this helps.

Gil

marshead wrote:Fridger et al,

Sorry to bring this up again after a few weeks (thats what one gets for moving office and being on vacation ).

You are right in noting that there has been a color shift in posted images. Unfortualtely, NASA is notorious for procesing images to make them look the most spectacular, not the most true to life. I have always been very critical of colors as seen in images, particularly of fainter fuzzies.

I can shed a little light on this subject through a very fortunate turn of events that resulted in my getting to look at Mars (and Uranus) through the 3.5m telescope at Apache Point Observatory the other night.

The big trick to being able to properly percieve color through a telescope comes down to aperture. With that much light gathering power, I believe that the color rendition on these fairly bright objects was as good as one can get it.

Of course, there is always a personal equation when it comes to percieving color, and it is likely that no two people will see the same color when looking at the same object. That said, I see the color of Mars as even LESS orange than the most recently posted HST images. It is close, but to my eye, it just doesn't look right. I see it as more to the yellow/beige than anything else. Remember that Martian soil is a mix of sand (like what we have here in the deserts of the southwestern US) and iron oxide as a first approximation. Take the two an mix together and you get a feel for what it is like.

Of course, the real answer can be best found by looking a a vial of Martian Soil Simulant produced by the Jet Propulsion Lab several years back. It is pulverized lava rock from Hawaii that has been procesed in such a way to match the spectral signature of Mars as close as possible (in other words the same color in all wavelengths). I have to dig up the small sample I have and take a closer look, but as I recall from that, my assertion that Mars is more yellow than orange is close.

Just my two cents worth. Hope this helps.

Gil

Hey Gil,

this is most interesting yet intriguing info! I tend to understand less and less...There is no doubt that in 8-12 inch telescopes Mars looks rather pinkish red (cf. also Praesepe's posts in the Physics and Astronomy department and his CCD images!). The biggest telescope I have used to look at Mars was about 1 meter quite a few years ago. Certainly the colour was not yellow-beige!

Anybody has a theory why theere seems to be a color shift from pink-rose to yellow-beige once you increase the telescope diameter?

[joke ON:
Are you sure that noone has secretly srewed a yellow filter to your eyepiece?;-).
[joke OFF]

With a 3.5 meter telescope, Mars must be incredibly bright without filters. It almost is too bright for my dark-adapted eyes even in my 8 inch at 500x. So I think I have enough light even in my scope for reasonable color rendition. What you mentioned is most relevant for weak nebulae/galaxies that typically appear colorless in smaller telescopes.

Bye Fridger

Here is another eyewitness report: I have only limited means for observation: the naked eye and binoculars... Nevertheless, I was curious what Mars would look like and looked at it one day before it was at it closest point to earth. It immediately struck me how yellowish it looked, while I did not expect this at all. I remember having seen mars at other times while it looked red. Could the height above the horizon have an influence (Mars was quite low above the horizon), or atmospheric conditions? I don't understand this either...

How colors look to the naked eye depends on many things. The same light can look a radically different color depending on the colors of things surrounding it, what you've just looked at, even the angular size of the object. Much of this is because of automatic adjustments in the brain intended to take into account the color of the lighting on a scene (so, I suppose, you can tell the poison berries from the yummy ones even at sunset). This "color constancy" mechanism gets flummoxed when what you're trying to gauge is the color of a light-emitting object, or of stars and planets against the blackness of space. So even to the naked eye, these colors tend to have a relative quality and are the subject of endless argument; witness any discussion of whether sunlight "really" looks yellow or white, or that flap a while back about the average color of the universe. I recently saw people arguing online over whether the backlight on an iPod is really bluish or not!

Hi all,
So there isn't a right or true colour? Then there is what looks right to most peoples pre-conception, (here I 'm reminded of the Moon colour debate elsewhere on the forum, I can't get used to the green Moon, even if it is how it looks from space). Perhaps there could be a function of similar principle to the limit of knowledge option, ie an "absolute" colour based on what a typical (or average) surface soil sample would look like under light of a given wavelength(s) or with whatever parameters anyone could care to define, so there was a convention, and a "view" colour, eg as seen from near orbit. How about a filter tool or option, to show infra red view, etc ?
Also, is anyone going to do a virtual tile-up of a 16k (or bigger) Mars?