WHATS THE DARK MATTER?

That's a great question, and one that astronomers can't answer. Even the smartest scientists in the world don't know what dark matter is. But they know it's out there. How?

All the planets, stars, galaxies and gas that can be seen today make up just 4 percent of the universe. The other 96 percent is made of stuff nobody can see, even with the most powerful telescopes. The strange stuff is actually two things: dark matter and dark energy. Astronomers know this stuff it out there because of the effects of gravity they can see on the objects that are observed.

If that has you feeling stumped, don't feel bad. Here’s how one really smart guy, science writer Richard Panek, thinks of it: "The overwhelming majority of the universe is: who knows?"

earths nebula

This photo was taken from space, but it's not a galaxy or a nebula. It's a massive phytoplankton bloom off the coast of South Africa, just when the Atlantic and the Indian oceans meet.

Right now it's summer in that part of the world. The phytoplankton—photosynthesizing microscopic organisms that have chlorophyll in their cells—is thriving thanks to the extended light times and the release of nutrients trapped in the melting ice.

Phytoplankton is crucial for planet Earth, as they produce more than half of the oxygen in our atmosphere, fix carbon and serve food for krill and other fish. They are the foundation of the sea and our planet.

The true-color image was captured by NASA's Terra satellite using its Moderate Resolution Imaging Spectroradiometer