What is Planet Nine?

Hypothesised undiscovered planet, 5–10 times the Earth’s mass, inferred from clustered orbits of distant icy objects.

Can you see it?

No — if Planet Nine exists at all, it is far too faint for any telescope you could point at it. Nobody has seen it yet.

Why it stands out: Not confirmed — still just a hypothesis; some scientists think the clustering could be a coincidence or an effect of which objects we happen to have found. A brand-new telescope in Chile, the Vera C. Rubin Observatory, started scanning the whole southern sky in 2026 and is considered the best chance yet to finally spot Planet Nine — or rule it out.; How we know: A small group of very distant icy objects have oddly similar, clustered orbits, as if something big and unseen is tugging on them with its gravity — first noticed in 2014 by Chad Trujillo and Scott Sheppard. Rung 3 of the cosmic ladder — how the solar system is arranged

The numbers

Distance from the Sun	possibly 400–800 AU