The Solar System’s outer limits
Thanks to recent discoveries, we now have a clearer picture of what lies beyond Pluto
Words by Andrew May
For 60 years after its discovery in 1930, Pluto – together with its largest moon Charon, discovered in 1978 – marked the outermost limit of the Solar System. With an average distance from the Sun of 39 astronomical units (AU) – with one AU the distance from Earth to the Sun – that’s pretty far out. But the 1990s saw the discovery of numerous other ‘trans-Neptunian objects’ beyond the orbit of Neptune, the most distant of the major planets, 30 AU from the Sun, with further discoveries coming in ever since.
Pluto actually resides in a relatively populous neighbourhood called the Kuiper Belt –a doughnut-shaped region extending from around 30 to 50 AU which contains hundreds of thousands of bodies larger than 62 miles in size.