The Kuiper Belt is a region beyond the Solar System that’s 20-times larger and up to 200-times heavier than the asteroid belt. It’s also littered with small icy bodies of volatile methane, ammonia and water. Here the number of large objects should be increasing the further through the belt you move, however, that’s really not the case at all. In fact the complete opposite happens – the belt all of a sudden drops off, quite drastically, just like a cliff. Meet the Kuiper Cliff – the unexpected outcome with no answer.
The Kuiper Belt isn’t just home to small bodies – dwarf planets Pluto, Makemake and Haumea are also thrown into the mix. However some scientists, including Patryk Lykawka of Kobe University in Japan, think that the Kuiper Cliff can be explained by some planet, perhaps the size of Earth or Mars, lurking somewhere as yet unseen by us, whose gravitational attraction is causing the Kuiper Belt to behave in such a way. The idea of a Planet X turned up the discovery of Pluto and for many years it was thought that a world, larger than Pluto, must exist undiscovered beyond it. Suggestions that this so-called Planet X was influencing Neptune’s orbit were quickly put to bed. However, the Kuiper Cliff has reopened the whole Planet X question once again.
With the likes of Voyager and Pioneer leaving the Solar System empty-handed – failing to find another planet – experts are once again becoming sceptical of the elusive planet. However, the chances of a spacecraft happening to fly past undiscovered worlds in such a vast amount of space are extremely unlikely, which means the jury is still out for Planet X until the Kuiper Cliff is finally explained.
Image Credit: John Hopkins University