In case you missed it, there was an extremely interesting discovery made recently. Scientists were able to recently find yet another example of Dark Matter, that seems to confirm earlier observations.
What is Dark Matter? This is a fairly good article explaining it. Suffice it to say that if our current models of astrophysics are correct (i.e. Einstein etc.) then the observed matter out there cannot really explain what we see . Galaxies are moving too fast, spinning too fast and the Universe is expanding too slowly for ordinary matter to explain it all. If the models are correct, there must be more unknown kinds of matter (i.e. matter that must be there, but which we haven't directly detected) as there are known kinds, in fact much much more. These exotic kinds of matter make up over 90% of all matter, yet we know nothing about it.
So, either we know nothing about 90% of matter, or our current models are wrong - which would be equally as troubling.
It's pretty heartening that we have found evidence that brings us closer to an understanding of these elusive unknown quantities.