"Their Face Lit Up"
Exploring the Reflective Face
In 2002 the 2001 Mars Odyssey spacecraft took spectra images of the Face at Cydonia that were unusually timed to coincide with the feeble Martian twilight before the sunrise. This revealed that the Face was reflecting back the lightening sky with far more intensity than nearby mounds and mesas.
These spectra images were taken with a "high exposure/gain" - to make the most of the limited amount of light being reflected from the ground - and were combined together to create a false colour image. Although the high exposure and subsequent processing produced an image that looked like the day-time , the official description for the images was "Cydonia - face at night" µµµ.
The Face's relative brightness can be seen below in the officially processed version of the image and one processed by Keith Laney µµµ. The latter image has been contrast enhanced to recreate the twilight effect at the time the image was taken.
(This article contains many large images that are best seen in "full screen" mode on internet browsers. Readers with a keyboard can get into full screen mode simply by pressing the F11 key - and then pressing F11 again when they want to return to the normal view. This and other browser control tips can be found here µµµ).
In an article titled "The Light Finally Dawns at Cydonia" the Enterprise Mission (TEM) concluded that not only did the Face have a high relative reflectivity, but that its absolute reflectivity was anomalously high in twilight lighting conditions. (See µµµ).
It's a Star in the Daytime too...
One of the joys of the Mars Global Reconnaissance (MRO)spacecraft is that its "low" resolution context camera - the CTX - produces images covering vast areas in useful detail. The CTX images are published to the internet in a format that has quite high brightness and contrast. This means that the details of very reflective surfaces get "washed out" in the glare.
......And in the CTX imagery of the Face a great deal of its surface is washed out in this way. The illustration below compares a CTX image of the Face with a more processed Mars Global Surveyor (MGS)image (on the left). It can be seen that a lot of the shadow throwing features on the western side of the Face are just lost in the reflective glare in the CTX version.
Further examination of the CTX imagery reveals that the Face is more consistently bright over its whole surface area than the other features in Cydonia.
This can be seen in the illustration below, which covers the familiar triangle formed by the Face, the D&M Pyramid and the City mounds. The second image in the illustration is gamma darkened. Gamma darkening darkens the dullest image pixels first, which has the useful effect of isolating the brightest parts of an image. Readers will find that their eye will tend to be drawn to the top left corner of each image, because of the Face's consistent brightness. (Source image here µµµ).
It is possible to more scientifically measure this "consistency of brightness". Image editing software allows users to draw boundaries around features and to get a histogram and statistics describing the brightness profile of the chosen area. The histogram is divided into 255 levels of brightness, with zero being totally black and 255 being pure white. The mouse cursor can then be used to read off from the histogram the number of image pixels matching any brightness level. In the illustration below, one such read-off is circled in red.
In the previous image of Cydonia there were two other features that had large areas of intense surface brightness. These were the Half-Face mesa and the Main Pyramid in the City mounds. In order to compare these with the Face boundaries were drawn around all three and histograms were made. (In the case of the Half-Face mesa the boundary drawn excluded some very dark cliffs on the eastern side. It was felt these would distort the statistics).
The following display sets out the results of this comparison.
The consistent brightness of the Face leaves its rivals "trailing in the dust". The average (median) brightness level for the Face is 224 - against 191 for both its rivals. The general Cydonia region only scores a dull 120.
Nearly 37% of the Face's surface is as bright as the 250 to 255 range - against less than 9% for the Main Pyramid, and less than 8% for the Half-Face mesa. Only 0.3% of the general Cydonia region was as bright as this.
In its relative Cydonia context the Face is exceptionally reflective.
The Mysterious Eye...
Keen eyed readers will have already noticed that while many normally shadow casting features on the west side of the Face have been "washed out", the "Ape-man" eye on this side has remained dark. This suggests that the "eye" is made of a light absorbing material, rather than of the highly reflective material surrounding it.
There is evidence from the 2001 Mars Odyssey's THEMIS camera that the "Ape-man" eye does have a different mineral composition from it's immediate surroundings. Although the THEMIS camera takes images in some visual spectra bands, most of the spectra bands it can image are actually in the invisible infra-red part of the spectrum. This infra-red imagery can be used to ascertain the mineral composition of different parts of the Martian surface.
Basically, materials of different mineral make-ups re-radiate the heat of the Sun in different parts of the infra-red spectrum. By taking several images in different parts of the IR spectrum almost simultaneously, of the same spot on the Martian surface, the THEMIS camera collects very detailed information about an area's geology. The standard way of analysing such multi-spectra IR images is to merge them together using a process called "de-correlation stretch". This gives a false colour to each of the bands in the IR spectrum and then emphasises where patches of the surface have unique IR spectra signatures. It is these unique signatures that will allow detailed mineral maps of Mars to be compiled one day.
Keith Laney compiles his own de-correlation stretch images from the THEMIS data published on the internet. He also overlays these images over existing visual imagery of the Martian surface - which is a standard geologist's technique. (See µµµ).
In one of Laney's de-correlation stretch images overlaid on the Face it is quite obvious (by the red colour) that the "eye" has a different mineral signature than it's immediate surroundings. This is shown below.
If the Face is considered as an artificial feature, then it would make sense for the builders to make the "eye" out of a different material that would really stand out - as it is still doing today.
The Twilight Saga...
We will conclude this investigation into the reflectivity of the Face by re-examining the twilight image that this article began with.
In the following illustration the low contrast published image (left) is subjected to extreme gamma darkening (on the right). The result of this exercise is that there are practically only three sources of reflected light remaining. These are the upper slopes of the D&M Pyramid, the eastern side of the Face, and the northern slope of the "Collapsed Mesa".
Only these three features in the image are the subjects of Cydonia Quest articles identifying their possible artificial nature. This is in itself is a significant result.
There are problems when trying to compare the relative brightness of the Face to the D&M Pyramid and "Collapsed Mesa" in the twilight image.
As the illustration above explains, the brightness of the "Collapsed Mesa" is being exaggerated a little by the lightening distortion that runs down the eastern edge of the image.
The "Collapsed Mesa" is also about five miles further east than the Face. Mars is a small planet with quite a tight curvature. It is likely that the twilight seen at the mesa is slightly brighter than that seen at the Face or D&M Pyramid as a result. (In contrast enhanced versions of the twilight image the ground gets darker as the view moves westwards. This could be a confirmation of a curvature effect).
Contrast enhancing the image does throw up a difference between the Face and the D&M Pyramid. As the contrast is increased the glow of the Face gets whiter, whilst the D&M Pyramid gets ruddier in colour.
(With normal colour images an increase in contrast only darkens or lightens colours. It does not usually cause colours to actually change. However, this does not seem to hold true for false colour images that are layered composites of different spectra bands. Increasing the contrast seems to bring out the band that shines the brightest - and so emphasise the colour that has been assigned to that band.)
Although the colour of the Face and D&M Pyramid looks the same in the published low contrast version, increasing the contrast is bringing out some difference in the way the two features are reflecting light.
One possibility is that the Face is more coherently reflecting light from all spectra bands upwards. Whereas the D&M Pyramid is scattering the light from some bands a little more. This possibility fits in with the Enterprise Mission's conclusion that the eastern side of the Face is reflecting the light of the twilight upwards with great directionality.
The preceding analysis does not address whether the Face has an anomalously high absolute reflectivity/albedo. Cydonia Quest does not currently have the resources to do this.
It does confirm that the Face can be singularly bright in the Cydonia context at both high Sun angles and during the twilight periods.
Moreover, the anomalously low albedo of the "Ape-man" eye and it's singular infra-red characteristics add to the suspicion that this feature of the Face was created by design.
In human civilisation monuments and monumental buildings are often deliberately built of the brightest materials so that they stand out. For example, the Giza pyramids were originally dressed with polished white limestone that gleamed in the sunlight, twilight and moonlight. Capital cities, such as Washington DC, are often filled with white monuments and official buildings.
If the Face is accepted as an artificial construct, then it must more than anything else be seen as a monument. It would be natural for its hypothetical builders to use the brightest materials available to make a strong visual statement. It is attractive to envisage a scene, millions of years ago, were the Face is floodlit at night and visible to spaceships approaching Cydonia.
µ The "Face" : Part 1
µ The "Face" : Part 2
µ The "Face" : Part 3
µ The "Face" : Part 4
µ The "Face" : Part 5
µ The "Face" : Part 6
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