posted on Mar, 6 2006 @ 04:30 PM
The problem is that once you get out to that far reaches, you can consider planetoids to be "Dark Matter". We can see far away galaxies because the
galaxies, for the most part, give off TONS of light. However, planets like Pluto, the earth, and all planets actually, DON'T give off light, but
instead reflect it.
This means that for us to see it, we have to have a close enough light source to it to reflect light off it. The smaller something is, the less light
is reflecting off of it, the harder it is to see. Also, as you get further and further away from a light source, fewer and fewer photons per area are
hitting it. After it reflects, then it also depends how far away WE are from that object, and how many photons reflect off of our mirrors into
In the end, you're left with VERY few photons per area for nonluminous objects. So much so that other stars lightyears away will overpower the light
that's being reflected - and so we can't spot the planets in the pictures.
Now, we can determine where planets "should be" by means of measuring the energy levels of a star system to the star, by measuring the "wobble" of
a star, and by other indirect means. This is why a planet can, for most purposes, be considered Dark Matter - because it's matter that doesn't emit
electromagnetic radiation (ie, light).
This is why it's so hard to see planets, even in our own solar system.