Planet nine is the hypothetical planet that we believe may be hiding in the solar system. Its existence is assumed based on the witnessed gravitational influence on a group of small, very distant objects with elongated, clustered orbits.
However, due to how far away planet Nine would be from the sun, it's likely that it would reflect very little sunlight thus can evade telescopes.
In order to defined as a planet, it must meet three criteria:
1. It must orbit a star, and not another planet
2. It must be spherical
3. It must clear its orbit, meaning that when it orbits it can push all the smaller bodies out of it's way making in the primary gravitational force in that ring
Pluto, for example, didn't meet this third criteria meaning its not longer considered out ninth planet.
For centuries, we have been looking up to the sky to understand the mysteries that surround us. The sky might hold the answers to some of our deepest questions such as where we came from. But what do we know so far?
Take a wander through human imagination, creativity & the designed world around us
Explore Planet Earth’s diverse environments & ecosystems, from rainforests to cities
Look back on key events, trends & people to shed new light on the world we live in today
Focus your attention inwards to one of the most complex systems of all: the human body
Immerse yourself in the world of words, written & spoken, from mythology to the media
Ask the knotty questions about knowledge, reality, existence, morality & what we believe
Delve into what drives us as humans, from communication & memory to thought & emotion
Journey through the natural world and the experiments & observations that illuminate it
Examine the ties that bind us as communities and the customs & structures we create
Investigate the most exciting applications of the cutting edge of research & thinking