Why can we see “earth like” planets that are light years away but still debate how many planets are in our own solar system?
In: Technology
Our only reliable way of detecting exoplanets currently is by recording the periodic dimming of the star as the planet passes in front. This mean that the ecliptic plane of the target system has to alight with our line of sight, which does not occur every time. So basically for every exoplanet we find there are possible millions we don’t see in the same area.
As to our solar system, some of the debate is about the classification of planets which doesn’t involved knowing if a planet is there or not. But yes some debate on the existence of planets further away, so how is this unreserved. Well consider the inverse square law: the light from the suns dims by the square of the distance to it. So for objects beyond Pluto or Neptune, the light hitting them get very small. If those objects are small in size, the effect is compounded. Now consider that light has to bounce off the planet (only a small fraction is reflected) and come back to earth, and that light too follows the inverse square law. By the time this light reaches the earth it is dimmer than far away stars and gets lost in the background noise so they are near impossible to observe. Their existence is theorized as an explanation for small perturbations is the orbits of known bodies which we are able to measure with some precision.
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