Two more planets in our Solar System: astronomers

The Solar System has at least two more planets waiting to be discovered beyond the orbit of Pluto, Spanish and British astronomers say.
      
The official list of planets in our star system runs to eight, with gas giant Neptune the outermost.
      
Beyond Neptune, Pluto was relegated to the status of "dwarf planet" by the International Astronomical Union in 2006, although it is still championed by some as the most distant planet from the Sun.
      
In a study published in the latest issue of the British journal Monthly Notices of the Royal Astronomical Society, researchers propose that "at least two" planets lie beyond Pluto.
      
Their calculations are based on the unusual orbital behaviour of very distant space rocks called extreme trans-Neptunian objects, or ETNOs.
      
In theory, ETNOs should be dispersed in a band some 150 Astronomical Units (AU) from the Sun.         An AU, a measurement of Solar System distance, is the span between Earth and the Sun -- nearly 150 million kilometres (almost 93 million miles).
      
ETNOs should also be more or less on the same orbital plane as the Solar System planets.
      
But observations of about a dozen ETNOs have suggested a quite different picture, the study says.
      
If correct, they imply that ETNOs are scattered much more widely, at between 150 and 525 AU, and with an orbital inclination of about 20 degrees.
      
To explain this anomaly, the study suggests some very large objects -- planets -- must be in the neighbourhood and their gravitational force is bossing the much smaller ETNOs around.
      
"This excess of objects with unexpected orbital parameters makes us believe that some invisible forces are altering...