Martian Orbit

Martian Orbit

When each of the two Viking orbit-lander combinations was inserted into Martian orbit, it was unalterably committed to landing at a certain latitude on Mars. If the low point in the orbit was at 21 degree Martian north latitude, the lander would touch down at 21 degree North, although, by waiting for the planet to turn beneath it, it could land at any longitude whatever. Thus the Viking science teams selected candidate latitudes for which there was more than one promising site. Viking I was targeted for 21 degree North. The prime site was in a region called Chryse (Greek for “the land of gold”), near the confluence of four sinuous channels thought to have been carved in previous epochs of Martian history by running water. The Chryse site seemed to satisfy all safety criteria. But the radar observations had been made nearby, not in the Chryse landing site itself. Radar observations of Chryse were made for the first time – because of the geometry of Earth and Mars, – only a few weeks before the nominal landing date.

Illustration: Elena

The candidate landing latitude for Viking 2 was 44 degrees North; the prime site, a locale called Cydonia, chosen because according to some theoretical arguments, there was a significant chance of small quantities of liquid water there, at least, at least at some time during the Martian Year. Since the Viking biology experiments were strongly oriented toward organisms that are comfortable in liquid water, some scientists held that the chance of Viking finding life would be substantially improved in Cydonia.

On the other hand, it was argued that, on so windy a planet as Mars, microorganisms should be everywhere if they are anywhere. There seemed to be merit to both positions, and it was difficult to decide between them. What was quite clear, however, was that 44 degree North was completely inaccessible to radar site-certification; the scientists had to accept a significant risk of failure with Viking 2 if it was committed to high northern latitudes. It was sometimes argued that if Viking 1 was down and working well the humans could afford to accept a greater risk with Viking 2. Carl Sagan found himself making very conservative recommendations on the fate of a billion-dollar mission. He could imagine, for example, a key instrument failure in Chryse just after an unfortunate crash landing in Cydonia. 

Grenadier Pond,  Toronto. Would the hopeful name of Utopia instead of banal Earth help the human race to overcome all the troubles? Image Light Colors by © Elena

To improve the Viking options, additional landing sites, geologically very different from Chryse and Cydonia, were selected in the radar-certified region near 4 degree South latitude. A decision on whether Viking 2 would set down at high or at low latitude was not made until virtually the last minute, when a place with the hopeful name of Utopia, at the same latitude as Cydonia, was chosen.