Voyager 2 enters Interstellar space

On November 5, 2018, after 41 years from launch, Voyager 2 left the area of the Sun's influence and joined Voyager 1 in a joint interstellar mission. Voyager 2 thus became another cosmic ship that reached the interstellar space. However, in order to understand the significance of this event, it is necessary to return to 1977 when both spacecraft were launched from Cape Canaveral.

Their mission was unprecedented, with the goal of touching the space outside the Solar System. First, Voyager 2 was launched, and after one month Voyager 1. However, since Voyager 1 fled the inner orbital path, he overtook Voyager 2 and first reached Jupiter. For this reason, it was named "Voyager 1". Both spacecraft left Jupiter and his moons in 1979, and then in 1980 they visited Saturn and its moon's system. During the encounter with Saturn, Voyager 1 gained acceleration upward leaving the planet and the solar system while Voyager 2 continued its flight to Uranus and Neptune, arrived in 1986 and 1987 respectively. While the spacecrafts were moving towards the end of the Solar System, they were within the heliosphere. The heliosphere resembles a huge protective balloon packed with plasma particles that throws out of the Sun in the form of jets. These particles form an integral part of the solar wind that surrounds the Sun and most of the Solar System's planets. The solar wind is expanding at a speed of 2 million kilometers per hour, far beyond the orbit of Pluto, until it collides with an upcoming interstellar wind. The boundary where this occurs is called heliopause, which separates the heliosphere from the interstellar environment. By the way, Voyager 2 are able to record the magnitude of the solar wind using the Plasma Science subsystem or PLS. Voyager 1 also carries its own PLS system, which unfortunately broke down in 1980, so only Voyager 2 gives scientists the ability to directly monitor the solar wind until the end of the heliopause.

On November 5, 2018, Voyager 2 detected a sharp drop of solar wind particles, while at the same time detecting a sudden increase in galactic cosmic rays. Cosmic rays are high energy protons that move extremely fast and they carry a lot of energy. These cosmic rays were accelerated by explosions of massive stars 10 or 20 million years ago. The sudden increase in the presence of cosmic rays, and the decline in the presence of solar wind particles, is evidence that Voyager 2 joined Voyager 1 in the interstellar space. Both spacecraft have now found themselves in a local interstellar cloud, which is about one hundred thousand times larger than the heliosphere. However, this cloud is incredibly weak - about a hundred trillion times less than clouds in our atmosphere. He is deserving that the solar heliosphere takes on the shape of a comet, as a result of the movement of the Sun and the Solar System through it.

Thanks to the correct PLS device which wear Voyager 2, scientists are able to determine whether the Sun has left or is not left a local cloud, or is it just moving to the neighboring so-called G cloud. These readings will literally help us to understand our place in the galaxy. Both spaceships continue to function and will continue to work as long as they have energy. Both spacecraft powered by a radio-isotopic thermal generator, which is a simple block of radioactive plutonium that breaks down over time. As plutonium decays, it produces heat that can then be used to start other spacecraft systems. However, the disintegration of plutonium by time, its strength weakens. Today, both spacecraft send signals with an output of about 20 watts. This is equivalent to the power needed to turn on the bulb in the fridge. Over time, their signals come to Earth but are extremely weak. To preserve the strength of Voyager 2, mission managers turned off the external camera on a spacecraft after passing next to Neptune in 1989. However, the output power of both spacecraft continues to decrease by about 4 watts each year. This means that mission managers will have to decide which instruments will have to exclude in the future in order to extend the interstellar mission of spacecraft.

Although both spacecraft have entered the interstellar space, they are in fact a long way to completely abandoning the Solar System. Both Voyager are 144 or 120 astronomical units away from the Sun. An astronomical unit is a measure that represents the distance from the Earth to the Sun. Thus, Neptune is about 30 astronomical units far away from the Sun. So, both spacecraft are 4 and 4.8 times away from the Sun than Neptune. But even this distance traveled is nothing compared to 1000 astronomical units, how much is the diameter of the Oort cloud - gigantic spheres full of small ice comets that have quietly orbiting around the Sun for millions of years. Our spacecrafts will take 300 years to reach the edge of the Oort cloud, and another 30,000 years to reach its other side. From that point of view, both spacecraft will be distant from Earth for more than one light year, and the Solar System will barely be seen from that distance. Their ultimate destiny is to orbital the Milky Way among its 400 billion stars. But even then the Voyager mission will be ready for its most important task. Each spacecraft carries a gold plate with music, sounds, images and greetings of people in 55 languages from the planet Earth. Plates represent a kind of message of humanity in the bottle, which the spacecrafts carries with them.

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Foto:Youtube printscreen / Launch Pad Astronomy