The 40-Year Voyages

Voyager 1 and 2

This summer 2017 marks 40 years since the launch of the Voyager spacecraft, the two most distant and longest-serving spacecraft in continual operation.

On 20 August 1977, Voyager 2 launched, followed shortly by Voyager 1 on 5 September. At the time, no one was sure if these probes would survive past their first mission – a fly-by of Saturn and Jupiter – but they defied all the odds and went on to discover much more.

Before the Voyager mission, very little was known about the gas giants of the outer Solar System. Jupiter and Saturn had only been observed closely by one other mission, the Pioneer probes, and Uranus and Neptune had never been visited. In fact, to this day, Voyager 2 remains the only spacecraft to have visited Uranus and Neptune.

The Voyagers have not only given astronomers brand-new information about each of the outer planets, they are also the furthest man-made objects from the Earth. And as of 25 August 2012, Voyager 1 officially left our Solar System, probing the space beyond our Sun’s reach for the first time.

Mission timeline: A once in a lifetime alignment

A record of humanity

Attached to the outside of each Voyager probe is a Golden Record – the 1970s equivalent of a USB stick. Similar to time capsules, these records were designed to inform intelligent alien life about humanity if the space probes were ever found. This sentiment is perhaps best summarised in the words of Jimmy Carter, former President of the USA, that were included on the records:

“This is a present from a small distant world, a token of our sounds, our science, our images, our music, our thoughts, and our feelings. We are attempting to survive our time so we may live into yours. We hope someday, having solved the problems we face, to join a community of galactic civilizations. This record represents our hope and our determination, and our good will in a vast and awesome universe.”

A variety of symbols are engraved on the front of each record, mostly depicting instructions for how to play it. Although designed for aliens, these instructions would almost certainly be necessary for anyone under the age of 30 here on Earth, such has been the pace of technology!

Two other diagrams show the Sun’s position relative to other stars, for navigational purposes, and the two lowest states of a hydrogen atom, which provides a reference for all the measurements used in the images on each record.

The record gives an impression of life on Earth in different cultures and through different time periods, and illustrates scientific and mathematical ideas, such as the numerical system we use, structure of atoms, and structure of DNA. These are shown as images, alongside photographs and diagrams of all aspects of life, including a developing foetus, a mother breastfeeding, buildings and transport, and the development of the space program. Also on the record are sounds of Earth, such as bird calls and other animal sounds, sounds of machinery, and noises of nature like wind and waves. There are greetings to whomever finds the space probes, given in 55 spoken languages, and music, ranging from traditional chants, to opera, to Chuck Berry’s ‘Johnny B. Goode’.

Planetary Voyage

The first leg of the Voyagers’ journey took them to Jupiter and its moons. In 1979, Voyager 1 made its closest approach of Jupiter, followed by Voyager 2 later in the year. Voyager was only the second mission to visit, so there were many unexpected discoveries. Three new moons were found – Thebe and Metis by Voyager 1, and then Adrastea by Voyager 2. Voyager also discovered that Jupiter had rings – a thin, icy band that had been never been seen before. And the Voyagers witnessed phenomena in the Jupiter system that had previously only ever been seen on Earth: lightning in Jupiter’s atmosphere, suggestions of an ocean on the moon Europa, and the biggest surprise of all, volcanoes on the moon Io, which was thought to be an inactive moon much like ours.

In November 1980, Voyager 1 passed by Saturn, followed in August 1981 by Voyager 2. In the Saturn system, four new moons were discovered. The temperature and weather conditions on Saturn were measured and the rings examined. Voyager showed the rings in better detail than ever before, and discovered a new ring and many smaller ringlets in the process.

After visiting Saturn, the paths of the two spacecraft diverged. Voyager 2 visited Uranus and Neptune, while Voyager 1 started its long journey to the edge of the Solar System and beyond.

After 40 years, Voyager 2 is still the only spacecraft to have visited the outer two gas giants, and there are currently no concrete plans for a trip in the near future. At Uranus, Voyager 2 showed the varied surfaces of the five known moons, including Umbriel, the mysteriously dark moon with one bright ring on the surface, and a bizarre patchwork moon, Miranda, which looks like it was possibly destroyed and later reformed. Eleven new moons were also discovered by the mission, and two new rings around Uranus.

Twelve years after leaving Earth, Voyager 2 arrived at its final planetary stop: Neptune.

Voyager 2 discovered six new moons orbiting Neptune, and it was the first spacecraft to image Neptune’s rings. Voyager discovered very dynamic weather on the planet, contrary to what was expected for such a serene-looking sphere. The winds on Neptune are the strongest in the Solar System, three times stronger than Jupiter’s famous storm, and a large anticyclone was observed in the atmosphere which astronomers called the Great Dark Spot. It has since disappeared.

On Valentine’s day, 1990, Voyager 1 took its last images: portraits of Neptune, Uranus, Saturn, Jupiter, Earth and Venus, from 6 billion kilometres away from the sun. The most iconic of these images is the one of our home planet and is commonly known as ‘The Pale Blue Dot‘.

After this, the camera was permanently switched off, and the interstellar mission began.

Into Interstellar Space

The aim of the interstellar mission is to find out more about what space is like outside of the Sun’s influence. In the Solar System, the Sun’s magnetic field and the plasma of the solar wind can be detected throughout, but the Voyager probes are making their way towards the parts of space where the Sun can no longer reach.

The boundary between the Solar System and interstellar space is called the heliopause, and marks the point where the pressure between the solar wind and the interstellar wind is balanced. Currently, Voyager 1 is the only man-made object to have passed this boundary, a feat it achieved on 25 August 2012 (listen to the sounds it heard of interstellar space). However, this is not universally agreed upon, as Voyager 1’s instrument for directly measuring the boundary is broken. Luckily, Voyager 2 still has a working instrument and when it passes through the boundary in about four years’ time, it will be clear. Voyager 1 and 2 are currently at around 20.8 and 17.2 billion kilometres from the Sun respectively, but are moving at very high speeds so these distances change rapidly.

To see where they are right now, explore NASA’s dedicated page.

Due to the old age and power consumption of the Voyager instruments, they will be gradually switched off one-by-one to save energy. The Voyagers are predicted to keep operating until 2020. After that, they will be left to drift silently. Voyager 1 is expected to pass within 1.6 light-years of a star in the constellation of Camelopardalis in 40,000 years. At this time, Voyager 2 will pass within 1.7 light-years of the star Ross 248, and in 296,000 years, it will pass within 4.3 light-years of the brightest star in the sky, Sirius.

For future billions of years, the Voyagers will continue to circle our Milky Way galaxy, beacons of humanity from a small, rocky planet called Earth.