Voyager 2
- 18th Aug 2022
- Author: Dhara Patel
The Voyager probes defy belief. In the early days of space exploration, twin spacecrafts were typically launched as there was such a high rate of failure, but amazingly, both continue to operate 45 years later. Originally planned for exploring the outer gas planets, the Voyager probes have now passed the heliopause, the boundary where the Sun’s solar wind becomes impeded by the interstellar medium.
Voyager 2’s Journey
Voyager 2 (about the size of an old Volkswagen Beetle) was launched on 20 August 1977, about a fortnight before its twin Voyager 1 set off on its journey. An alignment of the outer planets that occurs just once every 175 years made it possible to explore all the gas giant planets using a series of gravitational assists – whereby a spacecraft slingshots out to its destination using the gravitational attraction of a celestial body.
Voyager 1 visited Jupiter and Saturn before heading further out into the solar system. For some time, it held the record for the fastest speed achieved by a spacecraft – a whopping 61,500km/h, so although it left the Earth after Voyager 2, it crossed the boundary into interstellar space first, in August 2012.
Meanwhile, Voyager 2 flew by Jupiter and Saturn too, but also caught glimpses of Uranus and Neptune on its way out the solar system. As of 2022, Voyager 2 remains the only spacecraft to have ever visited the most distant planets of Uranus and Neptune and following in the footsteps of its twin, Voyager 1, it passed beyond the heliopause in November 2018.
Technically both spacecraft remain in the confines of the solar system and aren’t expected to pop out beyond the Oort cloud for another 14,000-28,000 years. The Voyager spacecraft are the most distant human-made objects, having surpassed the now-defunct Pioneer 10 and 11 probes launched in the early 1970s and they have the New Horizons spacecraft trailing in their footsteps.
Flyby of Jupiter
The primary aim of Voyager 2 was initially to explore Jupiter and Saturn (alike to its twin), but its mission was extended to then visit the distant ice giant worlds of our solar system – Uranus and Neptune. As such it became the first spacecraft to fly by all four planets in the outer solar system.
Voyager 1, although launched later, was on a faster trajectory so actually arrived at Jupiter months before Voyager 2. As such of its flyby in July 1979, Voyager 2 was able to observe changes in the planet compared to photographs taken by its twin and the Pioneer program. Viewing Jupiter from its shadowed side as it departed, allowed Voyager 2 to confirm the existence of thin rings around Jupiter that voyager 1 had seen.
It also discovered a new moon, later named Adrastea, which orbited Jupiter just outside its rings. And it saw cracks on the surface of its moon Europa, the first signs of the subsurface ocean of this moon, which was only hypothesised after the Galileo mission (1995-2003) once there was enough evidence to make the case.
Observations at Saturn
After a gravitational assist from Jupiter, Voyager 2 swung by Saturn in August 1981 to intensively study the planet, its rings, and moons. Because Voyager 1’s photopolarimeter instrument had failed by the time it reached Saturn, it was Voyager 2 that was able to observe and photograph the planet’s rings and ringlets at a much higher resolution.
In particular, it looked at the narrow, outermost “F” ring and helped to reveal that the Saturnian ring system is an intricate, detailed, and dynamic structure.
Voyager 2 also observed Enceladus – one of Saturn’s moons now known to harbour a global liquid ocean beneath its icy crust. Scientists noted how bright and pristine it looked with evidence of tectonic fractures. Before observations from Voyager, scientists weren’t sure the tiny 500km-wide world would be geologically active – a requisite for life to exist.
During its encounter with Saturn, Voyager 2 also imaged some of its other moons including Hyperion (the “hamburger moon”), Tethys, and Phoebe along with the more recently discovered satellites of Helene, Telesto, and Calypso.
Discovering Uranus and Neptune
After studying Saturn, the Voyagers departed company – Voyager 1 studied Saturn’s largest moon Titan before heading out of the solar system, whilst Voyager 2 continued on a path that would have it flyby Uranus in January 1986 – becoming the first and only spacecraft to visit this distant ice world.
It discovered ten new moons around Uranus (named after literary characters from Shakespeare’s works like Juliet, Desdemona, and Ophelia) along with two new rings on top of the nine previously known ones, and a tilted magnetic field. Interestingly it found that the average temperature of Uranus’ sun-facing pole was the same as that of the equatorial regions.
Continuing on from Uranus, Voyager 2 flew by Neptune in August 1989, and discovered five moons, four rings, and its Great Dark Spot – a huge spinning storm about the size of the entire Earth. The spacecraft studied Triton (Neptune’s largest moon) – the coldest known planetary body in the solar system – finding nitrogen ice volcanoes on its surface.
Voyager 2 helped to solve several questions that scientists had about the planet’s rings which were at the time believed to be arcs or partial rings. But observations revealed that Neptune’s rings actually are complete, it’s just that they’re so diffuse and made of such fine material that from Earth they could not be properly resolved.
Bon Voyage
As of August 2022, Voyager 2 lies roughly 19.5 billion km away (about 4.5 times further than the Sun-Neptune distance). It continues to fly out of our solar system at over 55,000km/h, but as it gets more distance the communication time delay increases (currently the one-way light time is 18 hours), and its power is dwindling.
All of the Voyager instruments are powered by a device known as a radioisotope thermoelectric generator (RTG) that converts heat from the radioactive decay of plutonium, into electricity. But because the material inside the RTG naturally decays, the fuel source has been diminishing over time.
Five of out 10 of Voyager 2’s instruments remain working but in the coming years, due to the power output falling by about 4 Watts a year, it’s likely that a few of those instruments will be turned off one-by-one in the hope that the remaining instruments can continue to ‘call home’ until 2030.
When there’s not enough power for even the last instrument, Voyager 2 will simply come to the end of its magnificent mission and continue its silent and eternal journey in the darkness of space.
They’ll eventually be able to escape the gravitational tug of our Sun and then head outwards across the galaxy years from now long after our Sun reaches the end of its life in about 4.5 billion years’ time.
Placed on the Voyager probes were golden records containing sights and sounds from Earth – perhaps if the spacecraft are ever intercepted by extra-terrestrial civilisations, they may come to know of our existence on Earth (we could be long gone by then)!
A Voyager Love Story
Cheers and celebrations to the longest continuously operating spacecraft in history.
Full image credits / references
(Banner image) The front of the 'Golden Record' aboard the Voyager spacecraft containing information about Earth and humanity. Credit: NASA
(1a) A model of the Voyager spacecraft. Credit: NASA
(1b) An illustration of the trajectories of Voyager 1 and Voyager 2. Credit: NASA/JPL-Caltech
(1c) This illustration shows the position of NASA's Voyager 1 and Voyager 2 probes, outside of the heliosphere, a protective bubble created by the Sun that extends well past the orbit of Pluto. Credit: NASA/JPL-Caltech
(1d) The five spacecraft whose trajectories have allowed them to escape the Sun's orbit. Credit: NASA/Johns Hopkins APL/SwRI
(2a) Voyager 2 image of Jupiter and its Great Red Spot. Credit: NASA
(2b) Voyager 2 image of Jupiter's thin ring system. Credit: NASA
(2c) Io with two volcanic eruptions, image taken by Voyager 2. Credit: NASA/JPL
(2d) Europa seen by Voyager 2. Credit: NASA
(3a) Voyager 2's view of Saturn as it flew past at a distance of 2.1 million miles. Credit: NASA
(3b) 'Spoke' features observed in the rings of Saturn. Credit: NASA/JPL
(3c) Saturn's moon Enceladus imaged during Voyager 2's closest approach to the planet. Credit: NASA
(3d) Atmosphere of Titan imaged by Voyager 2. Credit: NASA/JPL
(4a) An image of the planet Uranus taken by the spacecraft Voyager 2 in 1986. Credit: NASA/JPL
(4b) The rings of Uranus imaged by Voyager 2. Credit: NASA
(4c) The Great Dark Spot captured by Voyager 2 as it approached Neptune. Credit: NASA/JPL-Caltech
(4d) A colour mosaic of Neptune's moon Triton using data from Voyager 2. Credit: NASA/JPL/U.S. Geological Survey
(5) The back of the 'Golden Record' aboard the Voyager spacecraft containing information about Earth and humanity. Credit: NASA
(6) Video: A Voyager Love Story. Credit: The National Space Centre
