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Episode 74: The True Color of Mars

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Recap: The color of Mars seems like it should be something fairly simple to know and represent. Scientists claim to have solved it very early on, but a branch of conspiracy theories claims that, in fact, NASA and other space agencies have lied about the true color of Mars for decades.

Puzzler for Episode 74: Could scientists use the atmospheric measurements, looking at composition and particle size, to determine from first principles what the sky color should be?

Answer to Puzzler from Episode 73: There was no puzzler in episode 73.

Q&A: This episode's question comes from Johan S. from way back in August 2012. Of numerous questions he asked, the one I'm going to address in this episode is his third one: "How much dust is there at ground level [on Mars] and how fine is it? Is the atmospheric dust like a bit like a sandstorm, or more like forrest fire smoke? Are there environments on earth [sic] with similar dust such [as] high altitude deserts?"

The answer to this is both simple and difficult. Based on a list I found, typical dust sizes in Earth's atmosphere range anywhere from 0.001 µm to 1000 µm. The HUGE range of size is because on Earth, dust is made of many many MANY different things, such as spores and pollen, hair and skin, and smoke just to name a few. Smoke from wood in particular tends to have grain sizes from about 0.2 to 3 µm.

I found several different estimates for dust grain sizes at Mars, and the Phoenix lander back in 2009 actually imaged one grain to be about 1 µm. The numbers that I found generally estimate the average dust grain size to be around 1-3 µm, meaning they ARE about the same size as the average wood-derived smoke on Earth. You can easily get smaller stuff, but because of the much thinner atmosphere, it would be hard to get stuff 100x larger to stay in the atmosphere for any significant length of time.

To really simulate it, though, you probably would need to go into a lab. Earth has a much heavier atmosphere than Mars, so more large stuff can be suspended at once. You could go to the top of a mountain and get a bit closer to what it's like at Mars' surface, but it's still not very close. And, you have different gravity fields. And, on Mars, electrostatic forces play a larger role to help keep stuff separated and suspended in the much thinner atmosphere. So, the simple answer is that probably, no, you can't go to a similar environment on Earth to get a feel for the dust in the atmosphere of Mars.

Additional Materials:


Claim: I've been on a bit of a theme lately with image analysis, but I promise this is the last one for at least a month or two. The claim for this episode is that NASA and other world space agencies are secretly keeping the true color of Mars from all of us sheeple. The reason depends on who you listen to with explanations ranging from "just 'cause they can" to "because we'd realize that life could be there" or some such thing. [Clip from Coast to Coast AM, January 2, 2003, Hour 4, starting 0:51]

"The claim ... that NASA has deliberately and with careful forethought and knowledge distorted if not altered radically the colors of the images of Mars it has presented to us from various spacecraft missions going back now some 25-30 years."

Background: Color

For this topic, I really need to start off with background information. The normal human eye is a tricolor detector, with specific cells called "cones" that are sensitive to color. Some of the cones are sensitive to light that center around what we perceive as red. Some are sensitive to light that centers around what we perceive as green. The rest of the cones are sensitive to light that centers on what we perceive as blue.

Let's then say that a pure yellow light enters the average human eye. The cones that detect blue aren't going to be triggered really at all. The ones sensitive to green will be triggered a bit, and the ones sensitive to red will be triggered a bit. The human brain will then interpret that as yellow.

If a purple light enters the eye, the red cones won't fire, the green cones won't fire, but the blue ones will a little bit. The brain interprets that as purple. And again, this is all for a normal eye and a normal brain of a human. If you're color blind, blind, or have other eye issues or brain damage to the optical cortex, this may be different.

Anywho, that's how we perceive color. That's also how most color digital displays work, like TVs and computer monitors. In the old-school days of color photography with film and prints, it was paper that was sensitive to the different colors that the negatives were shined onto. But that's not really important for this discussion, though it gets one step closer to photos of Mars and from Mars.

Background: Color Calibration

The second bit of background is calibration. If you're a visual-normative human, your eyes and brain are color-calibrated. How you perceive color is not going to change.

Your television, computer, and camera can change.

If you're over 30 years old, you may remember the old days of cathode-ray tube televisions with individual knobs for red, green, and blue adjustment. If the picture looked too green, you could turn down the intensity of green. Same with red and blue. These days, the calibration on TVs and computer monitors is much better, and it's rare that you have to go into the settings and have to adjust the intensity of red, green, or blue. But if you do, what you've just done is color calibration.

Calibration is done in many different ways. The example I just gave is what I would term "winging it" or "fiddling with the knobs 'til it looks right."

If you're a pro or semi-pro photographer, then you'll know what white balance is. If you are a semi-pro or pro photographer and don't, then you should not be a semi-pro or pro photographer. Sorry ... you just shouldn't.

White balance is pretty much always set to "Auto" on every single camera, and most people never ever deal with it. Some will play with other built-in settings, such as a Tungsten light, or Daylight, or Clouds settings.

What all those settings do is adjust the balance of red, green, and blue when you take the photo. Other people, such as me, will just shoot every photo on Auto and then take it into raw image processing software such as Adobe Camera Raw in Photoshop, Adobe's Lightroom, or Apple's Aperture. In those professional software applications, you can very very finely tune the balance of red, green, and blue. When photographers do this, assuming they are going for a natural look, they adjust the balance until anything that was white actually appears white as opposed to red, yellow, green, cyan, blue, or purple, or something in-between.

For example, if you take a photo of a bride inside a building, her dress was almost certainly originally white, but in your photograph it's going to look yellowish simply due to the lighting. In software, you can decrease the amount of red and increase the amount of blue and get the dress to look white. When you do, every other color, assuming it was lit by the same light source, should look as it did to your eye when you were originally there.

The key point to this discussion is, that we fiddle with colors all the time. And, to make them look as "true-color" as possible, meaning as a visual-normative person would see them, we use anything that was white in the original image to go off of. If we don't have something that was white, then we try to use other cues, like a green plant, or our memory of something else.

The real pros, however, will use a calibration card. A calibration card for photography is literally just a printed card that has several shades of grey, from white to black, and many different standard colors on it. The photographer will put the card next to the object they're shooting, take the photo, and then remove the card and take the photo. Then, any color adjustment they do to the image with the card to make it look like it's supposed to is also the image adjustment they need to do to the shot without the card under the same lighting.

For pro photographers, proper lighting and color calibration can take the bulk of setup and editing time. For one wedding I shot, I spent well over 200 hours fine-tuning the color correction because there were four slightly different colors of lights in the room that made everything a pain in the buttocks.

Observing Mars

Now with color and calibration out of the way, let's go one step further and talk about the red planet. And right there, I mentioned a color. We've known ever since pre-recorded history that Mars is reddish in color. Many ancient cultures attributed it to their god of war because blood is also red. If you look at Mars with your unaided eye - again, assuming no vision issues - you will be able to tell that it's reddish. So, right off the bat, we go into this discussion KNOWING that Mars is in the red range of color, overall. And by "range" this includes orangish. But not blue.

Once telescopes got good enough that we could start to resolve Mars into a disk, observers saw that it wasn't a uniform color, but that it varied in places both in color and in brightness. Names of very large features are all based on these color and brightness differences.

And now I'm going to repeat myself a bit because we have to talk about how we know exactly what color Mars is. Or more realistically, the range of colors and that it does change.

In astronomy, when we want to very precisely measure the color of something, we have to calibrate based on something that's a known color. We also take pictures with several different filters and combine them into a color composite afterwards. For more on that, head back to episode 48 on image processing.

Across the sky there are what are called "standard stars." These are defined to a certain brightness at different standard filter colors. So what you do is take a picture of those with your filters, and then take a picture of what you want to photograph.

Let's do an example: Vega is a standard star, probably the most famous. Let's say I photograph Vega using the standard Red, Green, and Blue Johnson filter set (and there are MANY different standard filter sets, the Johnson being one of the most basic and widely used). So I take a photo of Vega in red, then green, then blue. Then I scroll over in the sky and take a photo of a galaxy in red, a photo of it in green, and a photo of it in blue. Then, just to make things easy, I go into photoshop and combine the galaxy into a three-color composite, and I do the same for Vega.

But when I do this, I see that Vega appears way too green. In other words, my detector recorded Vega being the correct brightness of blue relative to red, but it was too green relative to red. So I calibrate based on what Vega is defined to be, lowering the amount of green, until I get it to be what the standard calibration says Vega should be in terms of the balance of red, green, and blue.

Because Vega is my calibrator, I now have to make the exact same adjustment to the galaxy. Then, my galaxy is properly calibrated. If you understood the previous discussion about photographers using white balance, then this is really the exact same thing: White balance is to normal photographers as standard stars are for astrophotographers and astronomers. Exact same thing, but we do it more precisely in astronomy, worrying about how many photons there are at every single pixel.

With that in mind, we can use this type of calibration for Mars: Photograph a standard star and photograph Mars and you can figure out exactly the proper balance of your filters to get it to be a true color. When we do this, we find that the color varies somewhat over time. This is attributed to dust storms, wind blowing, seasonal frost, and other things. The difference isn't major -- it's not like it's changing hue from orange to green -- but it is noticeable.

And that's of course only if you're properly calibrated. And using the same filter set. If you just want to make a pretty picture, you can combine the filters in whatever balance you want and change the hue to what you want it to be. Want it more salmon color? Go for it. More rusty, you can do that too.

Observing from Mars

This is also what we do for photos taken from the surface of the planet. From what I could find, every single lander that at least the US has launched has had, effectively, a color calibration card on the lander. Exact same thing as professional photographers use. This allows people to properly know the balance of red, green, and blue, or whatever other filter set they're using, in order to get the colors to appear as though a visual-normative human were on the surface looking around. We also very precisely measure the color response of all the cameras while still in the lab on Earth and can calibrate that way, but that doesn't account for if things go wrong or degrade with time.

Knowing the color accurately is not only good for things like public outreach so you can say, "This is what it would look like if you were really standing on the surface of Mars!" but it's also important for geologists. For example, in the one geology lab class I took when I was an undergraduate, part of the lab final was to be able to identify 24 different rocks and minerals. One of the first ways we did this was by color. Like, plagioclase feldspar versus potassium feldspar look kinda the same except that potassium feldspar is salmon in color while plagioclase is more whiteish. Or obsidian, that's jet-black and shiny. Or when the Phoenix lander was digging in the dirt, it saw white material that disappeared in just a few days, indicating it was almost certainly ice. All of this interpretation would be much more difficult if we didn't have an accurate way to determine color.

But, there's one more complication. Well, many more, but this one factors into some conspiracies and claims. Cones in the human eye are sensitive to only a narrow range of wavelengths of light. We have yet to make an electronic detector that precisely mimics it, and there are often bleeds into other colors. For example, the Johnson blue filter I mentioned earlier has a red light leak. As in, it lets in blue light, no green, but then a little red. Similarly, dyes that we use to paint things aren't perfect.

Let's take the color calibrator on board the twin Mars Exploration Rovers. It's this one in particular that people point to for conspiracy-mongering. The color calibrator had a stripe of paint that, to a normal human eye, was red, another strip that's yellow, another green, and another blue. But, just like we can't get detectors perfect, we don't get dyes to be perfect. The dye used for the blue paint absorbs green and red and reflects blue, which is why to a normal eye it looks blue. But, it also reflects infrared light.

Most cameras sent to Mars have an infrared filter that allows photos to be taken in infrared light. In that filter, the blue color tab will be lit up because it's reflecting a lot of infrared light for the detector to receive through that filter. So, if you do something like a three-color composite of infrared, red, and green, that tab will be lit up, and there's a rather famous image that's used often online that shows a particular color composite where it's neon pink. Conspiracy-mongers will have you believe that this is proof NASA's hiding or faking or whatever-ing something, when in reality, it's just because of the kind of dye used in the paint used for the color calibrator. I'll link to an example of this in the shownotes.


So, I've jumped the gun a little and let my background info bleed into the conspiracy stuff. But now let's jump in all the way. The idea that NASA and other space agencies have lied about the "true color" of the planet Mars has been around for at least a few decades, but it's really hit its stride, as with many conspiracies, in the past decade or so with the rise of the internet and people fiddling around with photos without understanding what they're doing.

If you choose to do an internet search for "true color of Mars," you will get a lot of conspiracy sites. There's even a Facebook page for a "True Color of Mars" group. The possible motivation is something that no one's really sure about, and I'll address in a bit.

The alleged evidence for faking the color all gets down to calibration, which is why I spent so long talking about how we calibrate color. It also goes back all the way to the days of Viking.

In 1976, Viking 1 landed on Mars and returned the first color image from the surface. The story as some people tell it is that the image showed up on computer monitors or screens or something and it looked as though it were taken on Earth, complete with blue skies. Then, a few hours later, someone went around, boosted the red on all the images, and the head of NASA "demanded that the imaging team destroy the negative for the image [that looks like Arizona]."

This particular claim is one put forward by Richard Hoagland and others. I don't know how much of it is really true, but I do know that at least the last part is completely false. Remember that these were images were sent back to Earth via radio signal after being developed on the rover. The data were sent back to Earth and reconstructed through a multi-step process before finally being able to be displayed on a television monitor or printed onto photographic media. There's no such thing as a the original negatives for Viking lander images, which right away makes the conspiracy part of this highly dubious.

Assuming the first part of the story is correct, I can imagine a very mundane situation: The person who did the final processing from the downlinked data and put together the composite just scaled the colors until they thought it looked right and then broadcast the image to the scientist and press displays. It was a few hours later when they got an image with an actual calibration in there, or someone went to the guy who was processing them, and told them that no, based on these new calibration data, or based on how they think scattering of light by the dust in the atmosphere should work, the colors should be redder.

And because they changed, a conspiracy was born that persists to this day.

Other than the original Viking image I just discussed, and the bright pink that should be blue calibration strip for the Mars Exploration Rovers, that's really about it as far as specific claims go for this topic other than the general, "It should look like Earth."

There are numerous variations on this theme that I've seen and heard with conspiracy forums littered with them, YouTube videos, and of course Coast to Coast AM with their science advisor, Richard Hoagland.

Hoagland in particular wrote a two-part series on this for his website back in 2003, and he goes through a lot of what he says is the REAL calibration that SHOULD be done in order to prove his case.

It's a bit convoluted, so I'll probably lose some of you in describing it: He starts with taking a few photos from an amateur astronomer with the Portuguese last name of Cidadão ["see-dad-Ah-ö" according to an online pronunciation guide], which he pronounces consistently as "see-ah-DAR-ë-ö." So he takes this guy's Mars photos taken over the course of three weeks which all show the same color and claims that's the TRUE color of Mars. 'Cause of course, all of Cidadão's photos are properly calibrated and taken over many many years and show no variation. (That was sarcasm if you couldn't tell.)

He then takes those photos and manipulates all the NASA ones until they match Cidadão's in color and contrast. And because they're different from what NASA originally released, he says that NASA fakes them. Yes, I listened to Hoagland explain this for 40 minutes, and I listened literally at least 4 different times to make sure I was understanding it correctly. I also read his pages on this to check again, and I'll link to them so you can read them if you happen to be drunk one night with nothing better to do.

There are so many things wrong with this. I'll just list five that I thought of while listening to him ramble:

  • Mars' color varies on timescales of months to years to decades, not in the space of three weeks.
  • Cidadão's sequence shows no discussion of proper color calibration, and Hoagland cherry-picked one other amateur photo of Mars that's a similar color to claim that's the true color. Do an image search online for "amateur Mars photo" or "webcam Mars photo" and you'll get innumerable different variations of Mars' color.
  • The color-sensitive pixels in the webcam Cidadão used are completely different from the filters of Hubble and spacecraft orbiting Mars, which are all different from each other.
  • Hoagland's example of 9 different images from NASA showing 9 different colors are wrong because one of them is from MOLA, the Mars Orbiter Laser Altimeter which is sensitive to only ONE color, and one of the others he shows is black-and-white so of course it'll look different.
  • Photos he modified of NASA based on his calibration were never labeled as being true color or approximate true color.


Perhaps almost as interesting to this perhaps boring topic is WHY NASA would do such a thing. I've looked and listened around for this, trying to find what I considered a good reason, but I couldn't find it.

For example, here's one from a forum post on the GodlikeProductions forum: "I think they tamper with the colors to hide the truth and to make mars [sic] look very univiting [sic], baron [sic] and desert like."

On the same thread, another person wrote, "Why do you think the colors are actually Earth-like? Could it be because they actually ARE pictures of desert scenes FROM Earth?"

So, I've found claims like: (a) They want to make it look uninviting so we won't go there with people -- which is one of the stupidest I've seen because no federal agency DOESN'T want money; (b) they actually are on Earth and never got to Mars, so the conspiracy is that we can't get there and we're faking it; (c) or a modification of that being we faked it early on and made the sky red but once we actually did get there and found it to be blue, we had to change it so it stays red so no one knew we faked it early on; or (d) just because they CAN so they DO to keep the sheeple under control for some weird reason.

And Richard Hoagland has that weird reason that I think is conclusive enough to end the main segment with: [Clip from Coast to Coast AM, January 2, 2003, Hour 4, starting 28:35]

"If they've been lying about something as simple as the color, what else have they been lying to us about? ... [GN: Why?] ... Because Mars, and this goes back to the whole Sumerian/Iraqui/Saddam George ritual model. If there has been a literal transference of human beings from Mars in an incredibly distant era to Earth, refugees who came from a dying civilization ... and there were records preserved of that transfer, that we are Martians, and a select few have been-- have had access to those records, have held these sacred texts as the most precious documents at the core of their being because they're documents that go to the heart of the origins of the human race itself. And if these people, self-appointed, priests have formed a religion around this knowledge, obviously it would only be bequeathed to a chosen few! It wouldn't be for the many, it would be for the insiders, for the elites, for the guys that somehow think they're better than the rest of us and that they deserve to know and we don't."

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