Retargeting Cydonia

by Mark J. Carlotto, Ph. D.


On July 1, 1999 Mars Global Surveyor (MGS) will start a new mapping sequence that includes off-nadir data collections over the poles with the Mars Orbital Laser Altimeter (MOLA). (See for more information.)

Last April, prior to the main mapping phase of the mission, the Mars Orbital Camera (MOC) collected off-nadir images of the Face and targets in the City. Since that time no further imagery over the Face or any of the other objects of interest in Cydonia has been released. But whether any new imagery has actually been collected over these targets is not known.

[In the mapping phase up to the end of June 1999, the MOC aimed straight down, has been systematically imaging the Martian surface as the spacecraft orbits the planet. As a rough estimate, given the width of the narrow angle camera's field of view (approximately 2.8 km) and the distance around the ~40° circle of latitude for Cydonia (equatorial diameter = 6788, 6788 x cos 40° = 5200 km, 5200 x Pi = 16,336 km), one orbit in 5834 will pass over any given target, say the Face. As of the end of June, over 1300 mapping orbits were completed. At best, there is about a 22% chance that MGS has already flown over the Face.]

Given the widespread interest in Cydonia (mostly from outside of the planetary geology community), it seems reasonable to assume that the lack of new data released means that no new data has been collected. That MGS will be resuming off-nadir observations of Mars increases significantly the probability of successfully re-imaging the Cydonia targets.

But why should MGS re-image Cydonia. After all hasn't the matter been resolved?

The Face: Viking vs. MGS

In the 1970s, Viking took approximately 18 photographs of the Face and surrounding area at resolutions ranging from 43 to 889 meters/pixel. All images were collected during the spring and summer in Mars' northern hemisphere. The two highest resolution pictures, 35A72 and 70A13 were acquired in the summer with the sun in the northwest (late afternoon) and the spacecraft almost directly overhead.

Let us contrast these images to the single MGS high resolution image of the Face taken last April, SPO-1-220/03 (Table 1). That image was taken in the winter, with the sun to the south-southeast (mid morning), with the spacecraft about 45° off-nadir.


Viking 35A72

Viking 70A13

MGS SPO-1-220/03

LS (Season)

99 deg;


115 deg;


303.3 deg;






Solar Incidence

79.93 deg;

62.59 deg;

65.03 deg;

Solar Azimuth

268.8 deg;

266.5 deg;

159 deg;


10.58 deg;

12.42 deg;

44.68 deg;

Spacecraft Azimuth

323.32 deg;

319.04 deg;

232 deg;

Table 1 Comparison of high resolution Viking and MGS image acquisitions of the Face and nearby objects in Cydonia. The MGS and Viking images couldn't be any more different in terms of season, time of day, imaging geometry, and atmospheric state.

In the northern hemisphere, the quality of satellite images of Mars is sometimes reduced in the winter due to clouds and dust in the atmosphere. This can be seen in two wide angle (low resolution) images over Cydonia (Figure 1). The first was taken on April 5 (left) at the same time the Face was being imaged by the narrow angle (high resolution) camera. The second (right) was taken 9 days later when MGS attempted to image the City. In both images the surface is covered with patches of frost, most likely composed of water ice. The April 5 image is almost completely obscured by clouds. Even thought the area over the Face appears relatively clear, the atmosphere is still much hazier than it is in the April 14 image.


Figure 1 Wide angle (low resolution) images over Cydonia on April 5 (left) and April 14 (right).The April 5 image is much hazier and is almost completely obscured by clouds. Bright patches on the ground are probably water-ice frost.

That Viking never imaged this part of Mars in the winter, off nadir, in the morning, and under poor atmospheric conditions suggests that there is little real basis for comparing these images. Certainly there is no ground for either confirming or dismissing the artificiality of the Face based on the April 5 image and its similarity (or lack thereof) to the Viking imagery (Figure 2).


Figure 2 April 5 high resolution image of Face (left) and Viking 35A72 image reprojected to match MGS view. Although the images appear different the are many points of comparison.

Next Step

One year later, it is now summer in Mars' northern hemisphere. It is an ideal time for re-imaging the Face and other objects under conditions similar to those for Viking. Only then can the Viking-based predictions of facial characteristics, symmetry, and other factors be evaluated using MGS. MGS is also starting a new mapping sequence, one that will allow off-nadir viewing of selected targets on Mars.

So why not try to re-image Cydonia? Since the targets in Cydonia are a considerable distance from those at the poles, they should not compete for priority with the MOLA targets. The scientific case has not only been established, but established well beyond that required for any other target of interest on Mars. Not taking advantage of this opportunity could be a political mistake. It certainly would be a great loss to science.

(Page updated July, 1999)

© 2020 Mark J. Carlotto