Mars has always been a source of fascination for humankind, and dreams of traveling to the Red Planet are common in literature. In the last 65 years however, increasingly realistic plans have been proposed. The history of projects for human Mars missions is a long one. The most important cases are summarized in this chapter.
1.1 THE NINETEENTH CENTURY MARS
The Red Planet has for centuries fostered dreams and legends. Galileo, who in 1609 was the first man to clearly observe geographical features on an extraterrestrial body, the Moon, aimed his telescope also to Mars without succeeding in detecting anything except the fact that its disc was slightly flattened at the poles. The first person to claim to have seen something on Mars was Francesco Fontana who, in 1636, drew a rough map of the planet. Unfortunately it was later realized that the features he saw were optical illusions.
In the following centuries, generations of astronomers tried to map the surface of the Red Planet. Christian Huygens and Giandomenico Cassini succeeded in measuring the length of its day, which is now known as a sol . Cassinis value of 24 hours 40 minutes is remarkably close to the correct 24 hours 39.6 minutes. He also discovered the southern polar cap.
But distinguishing details on Mars was very difficult, and beyond the performance of the telescopes of those times. When telescopes powerful enough to see details on the planets disc became available, new surprises were at hand. The features were changing over time. In particular, the ice caps at the poles extended in winter and contracted in summer. Variations in the colors of the surface suggested the presence of vegetation. Darker areas were interpreted as seas. As a whole, Mars seemed to be a smaller sister of Earth: a living planet inhabited by an unknown flora and, perhaps, fauna. Now we know that most of the changes we see on the surface of Mars are due to sand and fine particles being blown around by the wind, but at that time there was no way to ascertain this.
In 1867, Richard Anthony Proctor drew a detailed map on which he assigned names to the various features. In 1869, Jules Janssen, using a spectroscope, concluded that although the atmosphere was thin there was water on the surface of the planet.
It was presumed that not only living creatures but also intelligent beings more or less similar to ourselves roamed on the surface of Mars.
In the latter half of the nineteenth century, three great astronomers, the Italian Giovanni Schiaparelli, the Frenchman Camille Flammarion, and the American Percival Lowell made a series of contributions both to the scientific knowledge and mythology concerning Mars. The former plotted a number of maps (e.g. Figure ) that remained an important reference until the first images to be received from a space probe completely changed our understanding of the planet.
Figure 1.1
A map of the two hemispheres of the planet Mars drawn by Schiaparelli following his observations during six oppositions between 1877 and 1888.
As shown in the figure, the maps drawn by astronomers were oriented in the same manner that they saw the planet in their telescopes, namely with south toward the top and the western limb on the right. Hence to compare the map of Figure , the former must be rotated 180.
Schiaparelli was the first to detect some thin dark features on the surface of the planet. He described these lines using the Italian word canali, which can be used both for artificial and natural water courses. However, the translation into English as canals was limited to artificial waterways and this led to many speculations about the civilization that might have undertaken such gigantic works of engineering, supposedly to survive the rapid process of desertification on their planet.
The idea that there were intelligent beings on Mars prompted many novels, ranging from The War of the Worlds by H.G. Wells to Under the Moons of Mars by E.R. Burroughs, and from Out of the Silent Planet by C.S. Lewis to The Martian Chronicles by Ray Bradbury to name just a few.
Although some of the classical misconceptions were corrected in the first half of the twentieth century notably, because there was neither oxygen nor water vapor in substantial quantity in the atmosphere, there could be very little water on the surface and the canals were an optical illusion our impression of the Red Planet continued to bear a striking resemblance to that of Schiaparelli and Lowell, except with it being a dry world possessing a thin atmosphere which was probably inhabited at least by some primitive forms of life. Intelligent beings, if still present, must have sought refuge underground. A common feature of many descriptions were the atmosphere machines, huge artifacts built by the intelligent Martians to maintain for as long as possible the conditions necessary for their survival. In many descriptions even some canals survived the likelihood that they were merely optical illusions.
This was the planet described by Wernher von Braun [] when popularizing his 1950s project for a human expedition to Mars.
By the 1960s, further astronomical work showed that if the planet hosted any form of life, that could only be the most primitive of species. Nevertheless, when Carl Sagan published an article in the National Geographic in 1965 and suggested that Mars lacked an ozone layer, he illustrated his article with hypothetical forms of life that had developed a protective layer against radiation from the Sun (Figure ).
Figure 1.2
Hypothetical forms of Martian life. Drawing by Douglas Chaffee for an article by Carl Sagan in National Geographic in 1965.
1.2 THE DISAPPOINTMENT OF THE PROBES
In 1960, just three years after launching Sputnik 1 as the first Earth satellite, the Soviet Union attempted to send two probes to fly past Mars. Mars 1960A and Mars 1960B each weighed 650 kg and carried a variety of scientific instruments. Both were lost when their rockets failed. At the next launch opportunity in 1962, the Russians launched three more probes. Two failed to start their interplanetary voyage and the third, designated Mars 1, was lost en route to the Red Planet. A further attempt in 1964 with the Zond 2 probe also failed.
In 1964, America tried its hand at Mars exploration by launching Mariner 3 and Mariner 4. Built by the Jet Propulsion Laboratory (JPL) , these probes were to fly close to the planet. The first mission failed, but the second, launched on November 28, reached its target on July 14, 1965. Twenty two pictures were recorded on tape on board and later transmitted to Earth over a period of 4 days. Altogether the images recorded about 1 percent of the surface of the planet.
Two of the pictures are shown in Figure . The one on the left is the first image ever received from Mars. It is an oblique view of the limb and covers an area of about 330 km by 1,200 km.
