Beyond the reach of the Sun is a fascinating region of the cosmos that we’re only just beginning to explore

Reported by Robert Lea

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The importance of the Sun to our little region of space is immeasurable, providing the light and energy that made life on T Earth possible billions of years ago and that continue to sustain us today. However, our star’s influence only extends so far. Beyond the reach of the Sun is a region of the cosmos called interstellar space. Though the first impression of this region may be a cold, empty stretch of space, the truth is that interstellar space is fascinating, exciting and not totally empty.

In many ways, interstellar space represents the ‘final frontier’ for space exploration, the dream of humanity extending its reach further than its own star and beyond its home planetary system. The distance to interstellar space and the distance to the next star is also a stunning example of how vast the cosmos truly is, highlighting humanity’s small place within it. And yet, our species, on a ball of mud and rock around a very average star, has already tested the waters of interstellar space with two active spacecraft.

Launched in 1977, the NASA spacecraft Voyager 1 and 2 left the Solar System in 2012 and 2018 respectively. Since then, the two missions have been collecting data from beyond the influence of the Sun. Voyager 1 is now the furthest human-built object from Earth at a whopping 24 billion kilometres (15 billion miles) away. That’s over 161 times the distance between Earth and the Sun, which is around 150 million kilometres (93 million miles), which is the basis of a unit of measurement called an astronomical unit, or AU. That means at a distance of around 161 AU, it takes about 20 hours for a signal travelling at light speed to journey between NASA’s Voyager team and the Voyager 1 spacecraft.

William Kurth is part of that team, serving as the principal investigator for the Voyager Plasma Wave Science investigation, whose work involves measuring naturally occurring waves in the charged particle environments of space. “Interstellar space is the stuff between the stars and the medium that pervades much of our galaxy. Voyager is making the first direct exploration of what is beyond our star’s own environment,” Kurth tells All About Space. “Specifically with Voyager, we are detecting a spectral feature that is directly related to the number of electrons per unit of volume, or the ‘plasma density,’ in the interstellar medium beyond the heliosphere, which is the volume of space dominated by the Sun’s plasma and magnetic fields.” He adds that plasma density is a fundamental property of various regions of space, and the observations made by the Voyager missions were the first direct measurements of this property in the interstellar medium. The Sun’s ‘bubble of influence’, the heliosphere, surrounds the entire Solar System. Its outer boundary, which marks the beginning of interstellar space, is called the heliopause.