On four occasions every 700 years, the planets align in a particular way. No, we aren’t taking to horoscopy all of a sudden. This rare planetary configuration that takes place once in every 175 years enables scientists to best utilise gravity assists.
The Voyager 2, which was in fact the first of the two Voyager spacecrafts to be launched, made use of exactly this. By making use of the gravity of one planet to sling itself to the next planet, Voyager 2 not only visited its initial targets of Jupiter and Saturn, but also made its way to Uranus and Neptune as well.
Image from August 1977 shows engineers working on the Voyager 2 spacecraft weeks before its launch on August 20.
| Photo Credit:
AP Photo/NASA
Launched on August 20, 1977, Voyager 2 sped past the asteroid belt between December 1977 and October 1978. During this period, its primary radio receiver failed in April 1978, and Voyager 2 has been operating using its backup receiver since then.
Jupiter encounter
Months after Voyager 1 made its closest approach to Jupiter, Voyager 2 made its closest approach of the planet on July 9, 1979 as part of a four-month encounter with the solar system’s largest planet. It then set out on its 29-month journey to Saturn, using Jupiter for a gravity assist.
As Voyager 1 had already had its successful encounter with Saturn, Voyager 2 was put to the task of studying some of Saturn’s moons that its twin couldn’t, before speeding towards Uranus and then Neptune. Long-range observations of Saturn began on June 5, 1981. As it got closer, the quality of images sent back kept getting better, including those of Saturn’s satellites Prometheus, Pandora, Iapetus, Hyperion, Titan, Enceladus, Janus, and Tethys.
Voyager 2’s view of Saturn and its ring system taken on August 11, 1981, when the spacecraft was 8.6 million miles away from the planet. The ring system’s shadow is clearly cast in the equatorial region.
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AP / THE HINDU ARCHIVES
Looks back at Saturn
Three days after making its closest approach – on August 25, 1981 – Voyager 2 turned its cameras on Saturn and returned spectacular images of the partially backlit planet. By September 28, when Voyager 2’s observations of the Saturn system was completed, the spacecraft had returned 16,000 images that included those of the planet, its rings and satellites.
The next day, Voyager 2 fired its thrusters, which enabled a course correction to send it towards Uranus. More than four years later, in January 1986, Voyager 2 became the first, and so far only, spacecraft to visit Uranus and its system, coming within 81,500 km of the planet’s cloud tops during closest approach. Before picking up a gravity assist from Uranus and heading off towards its final planetary encounter, Voyager 2 had discovered 10 new moons for Uranus, to go along with two new rings and magnetic field stronger than that of Saturn.
Low light challenge
Nearly 30 times as far from the sun as the Earth is, Neptune receives about one-thousandths the amount of sunlight that the Earth does. This posed a challenge for Voyager 2, as its camera would require longer exposures to get good images in such low light. The spacecraft’s speed meant that such long exposures would make the image blurry. To tackle this problem, the team programmed Voyager 2’s thrusters to fire gently during the close approach, in addition to rotating the spacecraft to allow the camera to stay focussed on its target, without actually changing the spacecraft’s speed and direction.
The “Great Dark Spot”, a storm in the atmosphere and the bright, light-blue smudge of clouds that accompanies the storm is seen on the planet Neptune, taken by the Voyager 2 less than five days before its closest approach of the planet on August 25, 1989.
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NASA/JPL-Caltech/Handout via REUTERS
With the Deep Space Network that was used to communicate with the Voyagers expanding its dishes, engineers could not only hear Voyager 2 clearly despite the huge distance, but also receive more data from the spacecraft during the Neptune flyby. Despite coming in the pre-internet era, the team involved made it a point to give the public frequent updates in the week leading up to the historic August 1989 flyby. What’s more, a programme called “Voyager All Night” broadcast regular updates on the day it made its closest approach.
First to Neptune
On August 25, 1989 – exactly eight years after a similar flyby with Saturn – Voyager 2 made its closest approach of Neptune, giving us humans the first glimpse ever of the eighth, and now, farthest planet, in the solar system. Voyager 2 showed that Neptune was a lot like Jupiter and Saturn, just with a blue-hue owing to the presence of methane. Six new satellites and four rings were discovered, in addition to a massive storm that was called the “Great Dark Spot,” similar to Jupiter’s Great Red Spot. Voyager 2 also made a close flyby of Triton, Neptune’s largest moon.
Two 10 minute exposures of Neptune’s rings clearly show the two main rings , as well as the inner faint ring and the faint band that extends planetward from roughly halfway between the two bright rings. These images were taken 1 hour and 27 minutes apart, using the clear filter on Voyager 2’s wide angle camera.
| Photo Credit:
Voyager 2 for NASA
The success story of Voyager 2 stretches way beyond August 25s and the flyby of Saturn and Neptune. The only spacecraft to visit each of the gas giants, Voyager 2 has now entered interstellar space to join its twin in an uncharted space. Both probes continue to report back to Earth, helping humanity to learn about a region where no other spacecraft have flown.
