30 years have passed since the first and only fly-by of Neptune by a space probe. It was August 25, 1989, and the Voyager 2 probe from NASA completed the Grand Tour, darting at only 4,950 km from the surface of the gas giant, and giving us unique, extraordinary close-ups.
The Voyager 2 probe was launched on August 20, 1977 from Cape Canaveral, shortly after its twin probe, the Voyager 1. As planned, the probe visited Jupiter and Saturn but, during the journey, the technicians realized that by exploiting a rare planetary alignment, it would also have been possible to reach Uranus and Neptune. The probe was then reprogrammed and Saturn’s gravity was used for a gravitational assist maneuver directed towards the icy giants.
This mission is a clear example of NASA‘s engineering ability. Reprogrammed from a distance, the probe has just missed its predetermined trajectory by 10 km. In the time since Uranus flew over three years earlier, NASA engineers worked tirelessly to improve the Deep Space Network, thus allowing the weak probe radio transmissions to be received on Earth, after a journey of over 4.5 billion of km.
The Voyager 2 probe allowed to discover 6 new Neptune satellites and to confirm also the presence of a weak ring system. Furthermore, it was possible to measure the mass of the planet, the average temperature and observe atmospheric phenomena. Subsequently, the probe passed about 40,000 km away from Triton, the largest moon in Neptune, discovering for example the presence of gaseous nitrogen geysers.
After leaving the Neptune system, the Voyager 2 probe was almost completely turned off, except for some instruments, to save as much energy as possible, and was directed towards the borders of the solar system. Currently the probe is located in interstellar space, at over 120 AU from the Sun, and if all goes well it will pass 4.3 light years from Sirius in about 296,000 years.