New Cydonia Images - April 2000

Mark Carlotto, Ph. D.
 

Two years after MGS reimaged the Face on April 5, 1998 MSSS/JPL released a handful of new images over Cydonia. Two cover the Fort in its entirety and one captured most of the Tholus. The Tholus was imaged in July 1999 while the two images of the Fort were taken in August and November (Table 1).

Like the earlier shots over Cydonia most of the new images were taken during the Martian winter when the atmosphere tends to be hazy and shadows not particularly well-defined. But unlike the off-nadir images taken in April 1998 during the Science Phasing Orbit the more recent Mapping Orbit images were acquired from almost directly overhead thus eliminating the geometrical distortions seen in the earlier images of the City and Face. Where the Science Phasing Orbit images over Cydonia were taken mid morning, the new Mapping Orbit images are shot at around 3PM.
 
 

Table 1 MGS Image Parameters (Courtesy MSSS/JPL)
 

The Fort

In Viking frame 35A72 the Fort appears to consist of three straight sides enclosing a triangular inner space. The topography of the Fort (Fig. 1) estimated from 35A72 using shape from shading shows the feature to be roughly delta-shaped with the northeast side missing. There are two peaks at the northern and southwestern vertices and an L-shaped depression just inside the northeastern edge. The impression of a three-sided object in the Viking image was created by the sun reflecting off the northwestern and southern sides and off the terrain sloping up to the northeast out of the L-shaped depression. With the sun to the northwest the shadow cast by the northern peak into this depression created the effect of a triangular inner space.

Fig. 1 Fort from Viking 35A72 (top left) and from MGS frames m04/01803 and m09/05394 (top right). Elevation image derived from 35A72 using single image shape from shading (bottom left) and elevation contours superimposed on new MGS image (bottom right).

With the illumination coming from south the Fort loses its geometrical appearance in the new MGS image. Up close it appears to be highly eroded like the Face and other objects that have been imaged. The comparison fade in Fig. 2 between the MGS and Viking images of the Fort shows that even though the straight edges are not as obvious in the new image because of the lighting geometry they are still there.

Fig. 2 Comparison fade between Viking and MGS images of the Fort

Using the Viking elevation model we can visualize the new MGS data in 3-D. Click here for a 360 deg. view of the Fort.

Tholus

The MGS image of the Tholus (m03/00766) appears much like the earlier Viking images albeit at a much higher resolution. The 'pit' seen in the Viking images appears to be a small crater in MGS and the 'grooves' look like either channels (runoff?) emanating from the crater, or a fracture surrounding the object. The central peak is well-defined. There is a shallow pit beside it. Click here for a 360 deg. view of the Tholus.
 

Fig. 3 Registered Viking and MGS images of the Tholus

Processed imagery Copyright © 2000 by Mark J. Carlotto. All rights reserved.

Original imagery courtesy MSSS/JPL.