In recent months several people claim to have discovered artificial objects in images of the surface of Mars sent back by Pathfinder. Some see distant structures like buildings and towers at the horizon, others see objects in the sky, and still others find machine parts lying around on the ground. In every case that I have examined, these "objects" turn out to be either image compression artifacts, seams between images that have not been corrected for geometrical distortions, or simply wishful seeing.
The fact that image compression is used for planetary imaging is not very well known and so will be discussed in some detail below. Anyone who has tried to mosaic several photographs into a panorama knows how difficult it is to get them to line up both in the near- and far-field. Several have mistaken misaligned seams between images as vertical objects in the distance (see McDaniel's discussion of the "Twin Peaks" controversy.) The problem of wishful seeing - of seeing things one would like to see but that are not really there - is one that continues to obfuscate the question of whether there are artificial structures on Mars and will be discussed at the end.
Because of the limited bandwidth (amount of information that can be transmitted from Pathfinder to Earth over a given amount of time), it is necessary to find ways to reduce the amount the information that has to be transmitted. Image compression reduces the number of bits needed to construct a picture. Image compression techniques take advantage of the fact that in most images there are regions with little or no detail that can be represented with just a few bits. While some techniques do not lose information, most do. In practice one can choose to save bits at the expense of reduced picture quality. Ideally, an image should be compressed to the point just before the picture quality becomes visually degraded. Often however this is not the case as we see in the Pathfinder images.
JPEG (or JPG) is one of the most common image compression techniques. It breaks an image into square regions, computes the discrete cosine transform of each region and keeps only the transform coefficients in coded form. The picture is reconstructed by the reverse process. Compression ratios around 10 to 1 can be achieved in most pictures without a perceivable loss of quality. (The compression ratio is the number of bits needed to store the original picture divided by the number of bits needed to store the compressed picture.) If the compression ratio is too high, i.e., if too little information is retained, the reconstructed image will be of poor quality with many artifacts.
The following example illustrates this effect. The picture below was taken in the English countryside. The image is almost lossless (about 7 to 1 compression ratio).
Below is the same picture after it has been severely compressed (about 63 to 1) using JPEG. Many artifacts are evident. Note the block-like regions throughout the image as well as fringes along the horizon.
Compare this to two 2X magnified regions in Pathfinder image rovertrek_sol38.jpg shown below. Notice the blockiness as well as the artifacts along the horizon. In the second image, two "objects" appear to be suspended in space over the horizon.
Not knowing about image compression, one could perhaps mistake a compression artifact for an artificial object. But after a moments reflection, one must ask, "Does it make sense?" Pathfinder landed in what is thought to be an outwash channel from a massive flood on Mars. Would one expect to find buildings in such a place, still standing? Or machine parts lying around on the ground? Or objects hovering over the horizon at just the right time and place to be imaged by the camera? It is not my intention to dismiss the efforts of those who have noticed these and other anomalies. Rather I want to emphasize the need for critical thinking and a more focused approach to the investigation of the Martian anomalies. I am concerned that such imaginative speculation will muddy the waters - adversely affecting the on-going debate about the Face and other anomalies in the Cydonia region of Mars.
Images returned by the Pathfinder seem to confirm that a catastrophic flood once occurred on Mars. Preliminary analyses indicate that several of the rocks may be sedimentary, suggesting that liquid water could have been present on the surface for an extended period of time. If so perhaps conditions on Mars were conducive at one time for someone to have constructed large artificial structures on the surface, for whatever reason.
Whether or not there are artificial structures on Mars remains an open question. But it is not one that can be answered by Pathfinder. For that we must wait to see what the Mars Global Surveyor finds.
(Updated November 1997)
|© 2020 Mark J. Carlotto|