Question: how do we know there isnt any more planets in space?

Enda O'Connell answered on 13 Nov 2012:

Hi Aoife

Astronomers and humans in general have been looking at the night sky for thousands of years and lots was known about our solar system before modern times. The Earth, Sun, Moon, Mercury, Venus, Mars, Juptier and Saturn were observed prehistory, while Uranus and Neptune were discovered in the past 250 years. Pluto was discovered in 1930, and was called a planet until 2006, when it was renamed a “Dwarf Planet”. For the past 150 years then, no new planets have been found in our Solar System and it is unlikely any more will be. Astronomers have searched the sky using telescopes, radio telescopes, satellites and using calculations which say that it is unlikely that any other planets are there as their size and gravitational pull would have an effect on the orbit of existing planets, which just isn’t seen.

However, if you are talking about exoplanets found outside our solar system, this is where it gets really interesting as a whopping 843 have been found, as of last week! In astronomy, one of the latest projects is the search for planets which might support human life, and a space observatory called Kepler was launched by NASA in 2009 to do just this http://kepler.nasa.gov/. As you’d imagine, the area where most people are looking is similar to where the Earth is found, orbiting a star like our Sun. The area where a habitable planet is most likely to be found is called the “Goldilocks Zone” and is not too far from the star to be too cold or too near which would be too hot, but is just right for life!