COLIN STUART ASTRONOMER AND AUTHOR
“All eyes are on the outer Solar System right now. First, astronomers found tantalising clues of a ninth planet beyond the orbit of Neptune. But now there might be a tenth, too.
We shouldn’t really be surprised. The early Solar System was a much more chaotic place than the largely serene environment of today. Another planet is thought to have whacked into the Earth to form the Moon, for example. What’s more, computer models of Solar System formation work better if there were more than four gas planets to begin with. Today’s gas planets were the gravitational victors in the Solar System’s childhood squabbles. Planets Nine and Ten, should they be confirmed, were likely bullied into far-flung orbits.
But why is it taking until now to find them? After all, we’ve found more than 4,000 planets beyond our Solar System. We don’t spot those exoplanets directly – we look for changes in the light from their host stars to infer their presence. For us to see a distant planet in our own Solar System, light has to trek from the Sun all the way out there and back to the Earth, fading all the while. So they’re on the edge of what we can seen with current telescopes. With the potential Planet Ten, the task is even trickier due to its likely position close to the bright Milky Way.
Should the planets be found, more than a decade since Pluto was knocked off its planetary perch, the textbooks will need ripping up again.”