At a distance of nearly 19 billion kilometres, the space probe Voyager 1 is the furthest manmade object from Earth and, as has recently been announced, is the first manmade object to leave our solar system – an astounding achievement that stands testament to mankind’s ingenuity.
Launched on 5 September 1977, Voyager 1 has spent the past 36 years sending back information from the outer solar system, along with its twin, Voyager 2. Taking advantage of an alignment of the four gas giant planets - Jupiter, Saturn, Uranus and Neptune - which occurs roughly every 175 years, the Voyager missions were officially designated to make close flybys of Jupiter and Saturn along with their respective moons, Io and Titan. After three years, Voyager 1’s path would, after visiting Titan, fling it out of the plane of the planets’ orbits and end its primary mission stage. Voyager 2 would carry on from Saturn, and make flybys of Neptune and Uranus, before it too started on a path out of the solar system after 12 years exploring the planets.
The Voyager mission’s planetary stage alone was a triumph – collecting astounding images and data, revealing hitherto unknown details of these distant bodies. Some of what was achieved includes: the discovery of volcanic activity on Jupiter’s moon Io (the first time such activity had been seen outside of planet Earth); observations of another of Jupiter’s moon, Europa, indicating the existence of an ocean beneath its crust; the discovery of 10 new moons around Uranus; the sending back of unprecedented detail of the rings around Saturn; and the atmosphere and weather of all four gas giants being studied in greater detail than ever before.
Since then, the Voyager probes have been on a heading out of the solar system, and have been collecting data on the Sun’s magnetic field, the make-up and direction of the solar wind, seeking to discover the details of a number of features thought to exist at the far reaches of the heliosphere – the region of space dominated by our Sun, a magnetic ‘bubble’ in which the solar system, the solar winds and the magnetic field of the Sun are contained.
In 2004, Voyager 1 reached the first of these features: the termination shock. This is the point at which solar winds, interacting with the interstellar medium (the gas, dust and cosmic rays that exist between star systems), are slowed down from supersonic to subsonic speeds (in other words, slowed down to below the speed of sound in the interstellar medium). Since then, it has been travelling in what is known as the heliosheath – a turbulent area in which the solar wind is further slowed as it encounters the interstellar medium.