Info

Atmosphere

Carbon dioxide

Strength of gravity

3.6 N/kg at surface

Mars as they flew past it. Later probes went into orbit around Mars and returned much more data. More recently, probes have successfully landed on the Martian surface, but to date no human has yet set foot on Mars.

The first three space probes directed at Mars were launched by the USSR between 1960 and 1962, but failed to leave Earth orbit. Mars 1, launched by the USSR on 1 November 1962, was the first probe to fly past the planet, but it failed to return data. The USA attempted a fly-by of Mars in November 1964 with Mariner 3, but its solar panels did not open and it is now in solar orbit. Mariner 4 arrived at Mars on 14 July 1965 and passed within 9920 kilometres of the planet's surface, sending back 22 black and white photographs of a barren, cratered surface. The thin atmosphere was confirmed to be composed of carbon dioxide, and a weak magnetic field was detected.

Mariner 6 arrived at Mars on 24 February 1969 and passed within 3437 kilometres of the planet's equator. Mariner 7 arrived on 5 August 1969 and passed within 3551 kilometres of the equator. The probes measured the atmospheric temperature and pressure, and surface composition. Together, the two probes took over 200 photographs.

The Mars 2 space probe reached Mars in 1971 and released a lander that crashed into the Martian surface when its rockets failed to slow it down. No data were returned, but it was the first human-made object to be placed on Mars. The Mars 2 orbiter returned data until 1972. Mars 3 arrived at Mars on 2 December 1971 and a lander was successfully placed on the surface, however it returned video data for only 20 seconds.

The first US spacecraft to enter an orbit around another planet was Mariner 9, on 3 November 1971. At the time of its arrival a huge dust storm was in progress on Mars and many experiments had to be delayed until the storm had finished. The probe sent back the first high-resolution images of the moons, Phobos and Deimos. Mariner 9 took over 7000 images of Mars and showed that giant volcanoes and river-like features exist on the surface. The probe is still in orbit around Mars.

Of the four separate probes launched by the USSR in 1973, Mars 5 was the most successful, going into orbit around Mars on 12 February 1974. It returned 70 high quality images to Earth.

Viking 1 went into orbit around Mars on 19 June 1976, and its lander touched down on 20 July. Viking 2 went into orbit on 24 July 1976, and its lander reached the surface on the opposite side of Mars on 7 August 1976. Both landers sent back a great deal of information about surface features and atmospheric conditions as well as conducting experiments to search for micro-organisms. No conclusive evidence of life was found. Pictures showed the Martian sky to be reddish as a result of the fine dust suspended in the atmosphere. The atmospheric pressure was found to be less than 1 per cent of that at the Earth's surface. The orbiters mapped the entire planet's surface, acquiring over 52 000 images.

Missions to Mars in the late 1980s were generally unsuccessful. In 1988 the USSR launched Phobos 1 and 2 to study the moons of Mars. Contact with Phobos 1 was lost en route to Mars as a result of a command error.

High Gain Antenna Mars Global Surveyor
Figure 7.2 Mars Global Surveyor.

Phobos 2 entered orbit around Mars on 30 January 1989, and came to within 120 kilometres of the moon before it failed.

The Mars Observer probe launched in 1992 by NASA was intended to provide the most detailed images of Mars ever obtained, but communications with it were lost just as it was about to enter orbit around the planet in August 1993.

The Mars Global Surveyor was the first mission of a new decade-long program of spacecraft to be sent to Mars. Launched on 7 November 1996, and consisting of an orbiter and robotic lander, the probe was designed to orbit Mars over a two-year period and collect data on the surface composition and features, atmospheric dynamics and magnetic field. The probe was inserted into a low altitude, nearly polar orbit on 12 September 1997 and it now circles Mars once every two hours. The mission has studied the entire Martian surface, atmosphere and interior, and has returned more data about the red planet than all other missions combined.

Mars Pathfinder was the first completed mission in NASA's Discovery Program of low-cost, rapidly developed planetary missions with specific scientific goals. Pathfinder arrived at Mars on 4 July 1997. It used an innovative method of directly entering the atmosphere, assisted by a parachute to slow its descent and a giant system of airbags to cushion the impact. The landing site was an ancient, rocky, flood plain in Mars's

Figure 7.3 The surface of Mars from Pathfinder Rover in 1997. (Photo: NASA)

northern hemisphere, known as Ares Vallis. Scientists believe a large volume of water cut the flood plain in a short period of time. A six-wheel robotic rover named Sojourner rolled onto the Martian surface on 6 July. Mars Pathfinder returned 2.6 billion bits of data, including more than 16 000 images from the lander and 550 images from the rover, as well as more than 15 chemical analyses of rocks and extensive data on winds and

Figure 7.4 Mars Pathfinder rover Sojourner and the rock 'Yogi'. (Photo: NASA)

High-gain antenna

Mars radiation environmental experiment (located inside)

High energy neutron detector

UHF antenna Thermal emission imaging system Neutron spectrometer

High-gain antenna

Mars radiation environmental experiment (located inside)

High energy neutron detector

UHF antenna Thermal emission imaging system Neutron spectrometer

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