The Voyager Legacy: How Two Spacecraft Changed Our View of the Cosmos
Have you ever wondered what lies beyond the planets of our solar system? How far can we explore the vastness of space? What mysteries await us in the interstellar medium? These are some of the questions that motivated the Voyager 1 and 2 missions, two twin spacecraft that were launched in 1977 and are still operating today, more than 45 years later. In this blog post, we will review some of the most amazing scientific discoveries that these spacecraft have made, and how they have transformed our understanding of the cosmos.
The Grand Tour of the Outer Planets
The Voyager 1 and 2 spacecraft were designed to take advantage of a rare alignment of the four giant planets of our solar system: Jupiter, Saturn, Uranus and Neptune. This alignment occurs only once every 175 years, and it allows a spacecraft to use the gravity of each planet to boost its speed and change its trajectory, enabling it to visit all four planets in a single mission. This is known as the Grand Tour, and it was a unique opportunity to explore the outer solar system in detail.
The Voyager 1 and 2 spacecraft were launched in 1977, two weeks apart from each other. Voyager 2 was actually launched first, on August 20, followed by Voyager 1 on September 5. The reason for this was that Voyager 1 had a faster and shorter trajectory, and it would reach Jupiter and Saturn before Voyager 2. This way, Voyager 1 could test the instruments and the communication system, and send back valuable data that could help Voyager 2 adjust its course and optimize its observations.
The first destination of the Voyager spacecraft was Jupiter, the largest and most massive planet in our solar system. Voyager 1 arrived at Jupiter in March 1979, followed by Voyager 2 in July. The spacecraft took thousands of images and measurements of the planet and its moons, revealing many surprising features. For example, they discovered that Jupiter has a powerful magnetic field and a complex system of rings, composed of dust and debris from its moons. They also found that Jupiter's atmosphere is turbulent and stormy, with winds reaching up to 600 km/h and a giant red spot that is actually a persistent hurricane larger than Earth.
But perhaps the most astonishing discovery was that one of Jupiter's moons, Io, has active volcanoes that spew sulfur and other materials into space. Io is the most volcanically active body in the solar system, and its eruptions are caused by the intense gravitational pull of Jupiter and its other moons, which deform and heat up Io's interior. The Voyager spacecraft captured stunning images of Io's volcanoes, some of which were erupting at the time of the flyby.
The next stop of the Voyager spacecraft was Saturn, the second-largest and the most beautiful planet in our solar system. Voyager 1 reached Saturn in November 1980, followed by Voyager 2 in August 1981. The spacecraft took spectacular images and measurements of the planet and its rings, which are composed of billions of ice and rock particles of different sizes and shapes, ranging from dust grains to boulders. The rings are divided into several sections by gaps and resonances with Saturn's moons, and they exhibit complex structures and patterns, such as waves, braids, spokes and arcs.
The Voyager spacecraft also discovered several new moons of Saturn, bringing the total number to 22 at the time. One of the most intriguing moons was Titan, the largest and the only one with a thick atmosphere. The atmosphere of Titan is mostly nitrogen, with traces of methane and other organic compounds. The Voyager spacecraft could not see through the dense clouds of Titan, but they detected that the moon has a surface pressure of about 1.5 times that of Earth, and a surface temperature of about -180°C. They also found that Titan has a weak magnetic field and a possible subsurface ocean of water and ammonia.
The Voyager 1 spacecraft ended its planetary tour at Saturn, as it was diverted to fly close to Titan and obtain more data. This maneuver caused Voyager 1 to leave the plane of the solar system and head towards interstellar space. The Voyager 2 spacecraft, however, continued its journey to the next two planets: Uranus and Neptune.
Uranus is the third-largest and the most tilted planet in our solar system. Its axis of rotation is almost parallel to the plane of its orbit, which means that it rotates on its side. This causes extreme seasons on Uranus, with each pole facing the Sun for 42 years, followed by 42 years of darkness. Voyager 2 arrived at Uranus in January 1986, and it was the first and only spacecraft to visit this planet. The spacecraft took images and measurements of Uranus and its moons, revealing a bland and featureless planet with a faint ring system and a weak magnetic field that is tilted 60 degrees from its axis of rotation. The spacecraft also discovered 10 new moons of Uranus, bringing the total number to 15 at the time. One of the most interesting moons was Miranda, which has a bizarre and varied terrain, with ridges, valleys, cliffs and craters, suggesting a violent and complex geological history.
Neptune is the fourth-largest and the most distant planet in our solar system. It is a cold and windy world, with the fastest winds in the solar system, reaching up to 2,100 km/h. Voyager 2 reached Neptune in August 1989, and it was also the first and only spacecraft to visit this planet. The spacecraft took images and measurements of Neptune and its moons, revealing a beautiful blue planet with a dynamic atmosphere and a powerful magnetic field that is tilted 47 degrees from its axis of rotation. The spacecraft also discovered six new moons of Neptune, bringing the total number to eight at the time. The most fascinating moon was Triton, which is the largest and the only one that orbits in the opposite direction of Neptune's rotation. Triton has a thin nitrogen atmosphere and a frozen surface covered with ice, snow and geysers that spout nitrogen gas and dust.
The Voyager 2 spacecraft completed its Grand Tour of the outer planets at Neptune, and it also left the plane of the solar system and headed towards interstellar space. The Voyager 1 and 2 spacecraft have visited more planets than any other mission in history, and they have made countless discoveries that have revolutionized our knowledge of the solar system and its diversity.
The Interstellar Mission
After their planetary encounters, the Voyager 1 and 2 spacecraft continued their journey to the edge of the solar system and beyond. Their new mission, called the Voyager Interstellar Mission (VIM), is to explore the outermost regions of the Sun's influence and to enter the interstellar medium, the space between the stars. The spacecraft are still communicating with Earth and sending back valuable data, despite being more than 20 billion kilometers away from us.
The Sun is the source of light and heat for our solar system, but it also produces a stream of charged particles called the solar wind, which flows outward in all directions. The solar wind creates a bubble around the Sun and the planets, called the heliosphere, which protects us from the interstellar radiation and cosmic rays. The heliosphere has several layers and boundaries, which the Voyager spacecraft have been exploring and crossing.
The first boundary is the termination shock, where the solar wind slows down abruptly as it encounters the pressure of the interstellar medium. The Voyager 1 spacecraft crossed the termination shock in December 2004, followed by Voyager 2 in August 2007. The second boundary is the heliopause, where the solar wind stops completely and the interstellar medium begins. The Voyager 1 spacecraft crossed the heliopause in August 2012, becoming the first human-made object to enter interstellar space. The Voyager 2 spacecraft crossed the heliopause in November 2018, joining its twin in the interstellar realm.
The third boundary is the bow shock, where the interstellar medium is compressed and heated by the motion of the heliosphere through the galaxy. However, the Voyager spacecraft have not detected this boundary yet, and some scientists think that it may not exist at all, as the heliosphere may be moving too slowly to create a shock wave.
The Voyager spacecraft are now exploring the interstellar medium, which is not empty, but filled with gas, dust, magnetic fields and cosmic rays. The spacecraft are measuring the properties and variations of these components, and comparing them with the conditions inside the heliosphere. The spacecraft are also searching for signs of other stars and their heliospheres, which may be nearby or far away.
The Voyager spacecraft are expected to keep operating until the mid-2020s, when their power sources will run out and they will go silent. However, they will continue to travel through the interstellar medium, carrying a message for any potential alien civilization that may encounter them. The message is a golden record, attached to each spacecraft, which contains sounds and images of Earth and its life forms, as well as greetings in 55 languages and music from different cultures. The golden record is a time capsule and a testament of our existence and our curiosity, as we reach out to the unknown.
The Voyager Legacy
The Voyager 1 and 2 spacecraft are the most successful and the longest-running missions in the history of space exploration. They have traveled farther than any other spacecraft, and they have visited more worlds than any other mission. They have made countless discoveries that have changed our view of the solar system and the cosmos, and they have inspired generations of scientists.
