What did my dream mean, it was about a planet nearing Earth?

I think you saw another world in life, approaching you.

A whole new world of experience or something like that.

It's not a disaster dream or negative, because it was peaceful, which is the nature of what the world represents.

But it was colourless, or grey, for some reason. So it may even be something new approaching you that you perceive as colourless or lifeless.

That it appeared with your mother suggests she is in with it, or it happened when she was there or because of her. But she spotted it suggests she saw it first.

You knew then exactly what it was, but of unknown origin suggests the unknown associated with anything new, or else the cause is unknown.

It passed the Earth must mean it passed quickly, not an ongoing thing.

The many moons orbiting must mean the parts to this main thing that come from it, or things that relate to it perhaps, that surround it, or orbit it so to speak.

What is it - or was it?

It sounds just like that film 'Melancholia'. That film was about depression. A good metaphor for depression is living on a Earth that is soon to collide with another planet. Maybe you are depressed, but this planet passed straight past so I'm not sure, are you just leaving a period of depression.

This may not have been the answer you were looking for, but its just my interpretation of your dream, hope it helps.

Apocalypse! 2012! The End Is Near! Rapture ! Your the chosen one ! End Of The World !

Just kidding :P

but maybe it can be interpreted as that something in your waking life that you see is a threat or a big event really isn't that big of a deal after all.

Intense dream. Are you sure your not high? IF not, you have a really good imagination. Mostly dreams come from what you watched the previous night or the night before.

I like cheese.

That u r werid