The heliosphere- the protective bubble of particles and magnetic fields created by the sun has been fired up by NASA’s Voyager 2 probe. The probe crossed the outer edge of the heliosphere on 5th Nov. The boundary where the tenuous, hot solar wind meets the cold, dense interstellar medium is termed as heliopause. Voyager 1 crossed the heliopause in 2012.
In 1980, an instrument (Plasma Science Experiment) stopped working on Voyager 1 long before that probe crossed the boundary but Voyager 2 carries a working instrument that will provide first-of-its kind observations of this gateway into interstellar space. Voyager 2 is slightly more than 11 billion miles i.e. 18 billion kilometers from earth, therefore it takes about 16.5 hours to travel from spacecraft to earth as light travels from the sun about eight minutes to reach earth.
Until now the space around Voyager 2 was filled fully with plasma flowing out from the sun. This flow is termed as solar wind which creates a bubble that involves the planets of the solar system. The PLS uses the electrical circuit of the plasma to detect the speed, density, temperature, pressure, and flux of the solar wind.
The PLS abroad Voyager 2 observed a steep decline in the speed of the solar wind particles on 5th November. Since then plasma instrument has observed no solar wind in the environment around Voyager 2 which makes to believe that the probe has left the heliosphere.
The two Voyagers provide a detailed glimpse of how our heliosphere interacts with the constant interstellar wind flowing from beyond. The boundary of the solar system is considered beyond the outer edge of the Oort cloud, a collection of small objects that are still under the influence of sun’s gravity.
Since the width of the Oort cloud is not known precisely but is estimated to begin about 1,000 astronomical unit(AU) from the sun and to extend about 100,000 AU. The Voyager probes are powered using heat from the decay of radioactive material. It is contained in a device known as RTG(Radioisotope Thermal Generator). The cameras on both spacecraft are turned off time to time to manage power since the power output of RGT decreases about 4 watts per year. The Voyager Interstellar Mission is a part of NASA’s Heliophysics System Observatory, sponsored by the Heliophysics Division of NASA’S Science Mission Directorate in Washington.
By: Karuna Aryal