The American space agency NASA (National Aeronautical and Space Agency) launched two space probes back in 1977. The twin spacecraft Voyager 1 and Voyager 2 were launched on 5 September 1977 and 20 August 1977 respectively from Cape Canaveral, Florida.
In 2012 NASA’s Voyager 1 became the first human-made or the first Earth object to cross the heliosphere and enter interstellar space. According to research published in “Nature Astronomy”, Voyager 2 became the 2nd earth object to enter the interstellar medium (ISM) by crossing the Heliosphere.
The Voyager 1 entered the interstellar space in August 2012 followed by Voyager 2 on 5th November 2018. However, the system instruments of Voyager 2 are in somewhat better shape than those of Voyager 1, so scientists were able to observe the transition from the heliosphere to the interstellar medium (ISM). Voyager 1 and Voyager 2 are still sending scientific information about their surroundings through the Deep Space Network, or DSN.
Scientists have confirmed Voyager 2’s locus into the Interstellar Medium (ISM) by noting a huge decline in heliospheric particles carried by the sun’s solar wind and a peculiar spike in plasma density detected by a plasma wave instrument on the Voyager 2.
The interstellar space is filled with high energy plasma and other cosmic rays which are left after the formation of the stars and solar systems. The heliosphere created by the sun’s solar wind protects us and our solar system from the interstellar wind with high energy cosmic rays coming from the rest of the Milky Way Galaxy.
What is Heliosphere, Heliosheath, and Heliopause?
The heliosphere is the final frontier of the influence of the sun, its giant plasma bubbles formed far beyond the dwarf planet Pluto and at the edge of the solar system. The heliosphere acts as a shield that protects the solar system including planet Earth from galactic cosmic radiation. The heliosphere is formed by the encounter of interstellar wind and the constant burst of the solar wind.
What are Solar Wind and Solar Storms?
The outer layer of Sun called Corona bursts supersonic plasma containing mostly charged particles electrons, protons, and alpha particles in all directions from the sun. The bursting or streaming of plasma from the Corona is called the solar wind.
These rapidly moving charged particles are able to escape the Sun’s intense gravity because of the immense high temperature of the Sun’s Corona, which reaches up to a million degrees Celsius. The solar wind varies in density, temperature and speed over time and over solar latitude and longitude. The speed of solar wind may reach around 700 kilometres per second.
The solar wind carrying charged particles and magnetic clouds from the Sun can harm the earth badly with its radiations if it hits the planet directly. Luckily, Earth’s magnetic field called the magnetosphere similar to the heliosphere which serves as a shield and redirects the solar wind materials around the planet so that they stream beyond it.
The force of the wind stretches out the magnetosphere so that it is smooshed inward on the sun side and stretched out on the night side. The encounter of Earth’s magnetic field with solar wind causes the Aurora on Earth’s pole. When the sun streams out large bursts of plasma then it’s called the solar storm or coronal mass ejections (CMEs).
Termination Shock:
The termination shock is the starting area of the heliosphere. When the solar wind travels far from the Sun, even far beyond the dwarf planet Pluto’s region until it starts getting impeded by the interstellar medium. At this point, the speed of the solar wind drops abruptly as it begins to feel the effects of interstellar plasma permeating in the galaxy also called interstellar wind.
Heliosheath, Heliopause, and Bow Shock:
The outer region of the heliosphere is called the heliosheath. Here the solar wind gets denser and piles up as it presses outward against the approaching wind in interstellar space. The edge of the heliosphere is called heliopause which is the boundary between the solar wind and the interstellar wind. Here, both winds have the balance pressure and it also causes the solar wind to turn back and flow down to the tail of the heliosphere.
Bow Shock is the front nose of the Heliosphere, it is the area where the heliosphere formed by the solar wind collides with the surrounding interstellar medium (ISM).
The twin Voyager probe spacecraft have explored and entered interstellar space passing through the termination shock and the heliosheath and heliopause. Voyager 1 currently moving approx 62,140 km/h relative to the Sun and it has crossed the heliopause and entered the interstellar medium on 20 August 2012.
Now, scientists have confirmed in the journal published in Nature Astronomy that Voyager 2 crossed the heliopause on 5th November 2018, and entered interstellar medium (ISM). Both Voyager probes have launched at different trajectories, Voyager 2 crossed the heliopause at 119.7 astronomical units (AU-distance between earth and sun), or more than 11 billion miles from the Sun, however, Voyager 1 has passed the ISM at 122.6 AU.
Golden Record on Voyager Spacecraft:
Voyager 1 and Voyager 2 have made an extraordinary milestone in space exploration by entering the interstellar medium which is around ten times beyond the solar system’s dwarf planet Pluto.
Voyager 1 and Voyager 2 are not alone there in ISM or deep space, the entire human race, Earth and the solar system are with these space probes. Each Voyager space probe carries a gold-plated audio-visual disc which has all the information about us and location of our solar system in the galaxy and the location of planet Earth in our solar system.
It was an astrophysicist Carl Sagan’s idea to put the Disk called “Golden Record” on twin probes, so that if any of these spacecraft ever found by any intelligent life form from other planetary systems will come to know about us, earth and our solar system.
Astrophysicists Carl Sagan and Frank Drake collaborated with historians, artists, folklorists and ethnomusicologists to create the best first impression of our home planet via Golden Record. The Golden Record has 116 analogue-encoded images, greetings in 55 languages, 12 minutes of natural sounds from Earth, and 90 minutes of music, including the Indian classical song “Jaat Kahan Ho..” by Surshri Kesar Bai Kerkar.
However, space is so vast that even if Voyager’s twin is found by some alien world, will there be anyone on Earth to know that? The nearest star system called Alpha Century System is 4.7 light-years from us. Voyager 1 and Voyager 2 do not have the energy to run their instruments and to communicate with Earth for very long, in the next 5-7 years NASA will lose all communications with the Voyager probes.
Voyager 1 the farthest space probe will still be travelling in never-ending deep space after losing communication with the Earth. Hypothetically, even if it keeps going towards the Alpha Century System with its current speed which is 62,140 km/h (relative to the Sun) still it will take around 72,000 Earth years to reach the nearest star of the Alpha Century Star System called Proxima Century; by then a lot will be changed here on earth and in our solar system.
