No Dark Matter Here

Dark matter is a concept, not a thing. When astronomers add up all the mass they can see in a galaxy -- stars, glowing dust -- and compare it to the gravitational effect galaxies have on each other, they find that 90 percent of the mass is "missing." Something we can't see dominates the gravitational universe. We call that "dark matter," but we have no idea what it is.

Now one group of astronomers has undertaken an exhaustive search for dark matter in our own solar system. They measured the gravitational effect that our system has on nearby stars and concluded that what we can see accounts for most if not all of the observed mass. According to their measurements, no more than 20 percent of the matter in our solar system can be "dark."

Some models of dark matter assume that it should be evenly distributed through space, or at least through galactic space. But if this finding holds up and there is no dark matter in our solar system, it's bye-bye to those models and back to wondering if the dark matter is in black holes or invisible clouds, none of which happen to be near us. Or some effect that is only observable at very large distances, or something even weirder.

Our ignorance of the universe is profound.