THE PLANETS THAT SHOULDN'T EXIST

With sapphire waterfalls, lava rain and orbits around dead stars, these distant worlds push the limits of what's possible

- by DR GEORGE DRANSFIELD

Isn’t it amazing that astronomy – humanity's oldest science – continues to generate such a delightful amount of new knowledge? Seeing as we've been studying the motion of the stars for a good long while, you'd be forgiven for thinking that, by now, we would be long past the point of saying “Astronomy? Completed it, mate.”

Fortunately, the Universe is vast and unknowable. However big our telescope mirrors and however sensitive our detectors, there will always be some light that's too faint to see and signals that are too weak to detect. This is good; for one thing, it means I still have a job; more importantly, however, it means the sky is still full of wonder.

Planets are one such wonder. The word 'planet' comes from the Greek 'planētēs', meaning 'wanderer'. They were so named because our closest planetary siblings in the Solar System appeared to wander across the night sky. Alas, detecting our distant planetary cousins – the exoplanets that lie beyond the Solar System – takes far more effort than glancing skyward once the Sun has set. It requires enormous telescopes, long observing campaigns and a lot of computing. But believe me when I tell you, it's worth the effort.

Exoplanet detection is booming. At the time of writing, astronomers have discovered almost 6,000 of them and we think that most stars have them. But of course, in a field characterised by so many discoveries, occasionally truly extraordinary things turn up. There have been planets that flirt with the line separating science and science fiction; planets that force us to revisit our theories of how they form; and planets that, in all fairness, feel like they shouldn't exist. Planets like the 10 that follow…

THE PLANET TOO BIG FOR ITS STAR