The Giant Planet Hiding in Our Backyard

Despite our tech-savvy telescopes and galaxy-spanning observations, we might have missed something massive right here in our own solar system. No offence, Pluto.

Planet Nine, if it exists, could be ten times the mass of Earth and four times its radius. A heavyweight hiding in the shadows, tugging at distant asteroids with its invisible gravitational tentacles like some kind of celestial puppet master.

So why haven’t we seen it? Well, it’s far—600 AU from the Sun, to be precise. That’s twenty times further than Neptune. And although we've spotted exoplanets millions of times further away, the irony is that our methods for doing so—like transit photometry—don’t work well within our own solar system. It's like finding a yeti in the Himalayas while being oblivious to the one in your garden.

The hunt began over a century ago with a chap named Percival Lowell. He thought Uranus and Neptune were being pulled slightly off course. Turned out they weren’t—we’d just miscalculated Neptune’s mass. Classic.

But modern astronomers like Konstantin Batygin and Mike Brown (yes, the very man who got Pluto demoted) noticed oddities in the orbits of objects beyond Neptune—ETNOs. They’re oddly aligned and weirdly behaved, possibly thanks to Planet Nine.

Sceptical? So are many scientists. Some even suggest a tiny black hole could be responsible instead. But whether it's a mystery planet or a grapefruit-sized black hole from the dawn of time, one thing’s clear—we still don’t know everything about our own solar system.

So, is Planet Nine out there? No one knows for sure. But we’re watching the skies. Closely.
...
https://www.youtube.com/watch?v=baAkptnBGV8