Exploration of Mercury - Mariner 10

Mariner 10

Mariner 10 was a probe whose primary objective was to observe the atmosphere, surface, and physical characteristics of Mercury and Venus. It was a low-cost mission completed for under $98 million. Mariner 10 was launched at 21:45 PST on November 2, 1973, from Cape Kennedy. Since Mercury is so close to the Sun it was too difficult to incorporate an orbit around Mercury in the route so Mariner 10 orbited the Sun. In order to reach its destination, the satellite was accelerated with the gravity field of Venus. It then passed close to Mercury on March 29, 1974, as it flew towards the Sun. This was the first observation made of Mercury at close range. After the encounter Mariner 10 was in an orbit around the Sun such that for every one of its orbits Mercury made two, and the spacecraft and the planet would be able to meet again. This allowed the probe to pass by Mercury two additional times before completing the mission; these encounters were made on September 21, 1974, and March 16, 1975. However, since the same side of Mercury was illuminated during each of the flybys, at the conclusion of the mission Mariner 10 had only photographed 45% of its surface. The mission ended as fuel of the probe ran out in March 24, 1975. As the spacecraft was no longer controllable without fuel, a command was sent to the probe to shut down its transmitter.

The close observations collected two important sets of data. The probe detected Mercury’s magnetic field, which is very similar to Earth’s. This was a surprise to scientists, because Mercury spins so slowly on its axis. Secondly, visual data was provided, which showed the high number of craters on the surface of the planet. The visual data also allowed scientists to determine that Mercury had “not experienced significant crustal modification”. This also added to the mystery of the magnetic field, as it was previously believed that the magnetic fields are caused by a molten dynamo effect, but since there was little crustal modification this undermined that idea. The visual data also allowed scientists to investigate the composition and age of the planet.