The transit of Kepler 22-B...

[sandyRoe]

The light from a distant stat appears to dim as a planet crosses between it and Earth.
How can the scientists know that it's similar in size to earth, might have liquid water, and might even have life on it?

[albaqwerty]

I can't prove or disprove either way, but it might have something to do with all these wonderful telescopes and satelites which have been sent into space.

[McMouse]

If life is discovered on a distant planet our scientists will be wetting themselves in an effort to communicate. I think their time would be better spent perfecting conversation, here on earth, with goldfish.

[john1066]

will they be driving around in Bmw's and Mercs?

[jake-the-peg]

They can tell it's of similar size by it's orbital characteristics.

If you know the mass of the star and it's size you can tell how far away the planet is from the star by thingslike how long it takes to transit and that tells you the planets mass.

You know how hot the star is from the characteristics of it's light so you have a pretty good idea from that how much heat the planet is intercepting.

That can be significantly out from atmospheric conditions - eg Venus is hotter than Mercury due to it's atmosphere.

After that it becomes more speculative. Water is pretty common sogien the right temperatures there should be liquid water.

Life arose very rapidly on Earth almost as soon as it could so the smart money is that it's pretty common.

Complex life's ntherissue - the life could just be slime