Voyager 1, distant ambassador….Credit: NASA
Take a brief moment to think about Voyager 1, the very first human-made thing to leave our Solar System. Voyager 1 is a probe launched by the American space agency NASA in 1977 (make that 34 years and 9 months ago), which is now tootling along through the heliosheath, the outermost layer of the heliosphere, the last vestige of space influenced by the particles emitted from our Sun. From the perspective of Earth our Solar System is a big place. Where Voyager is now is about 11 billion (yes, billion) miles (more than 17 billion kilometers) from Earth. In scientific jargon, that’s 120 AU, (astronomical units or the distance from Earth to Sun) and puts it – possibly – outside the Solar System. I say possibly because the ‘boundary’ is difficult to measure, in fact, more or less theoretical. Also the heliosphere is irregular; we know there are thicker and thinner portions, so Voyager could be said to be ‘on average’ outside this Solar System, but in reality still be in a bump of the heliosphere. A mere quibble, really, compared to the vastness of outer space. The main point is that we’re still communicating with Voyager, still learning from it, after all this time and distance. It’s a bit of a human achievement worthy of a moment’s acknowledgement.