Flexi Says: Actual humans have not made it very far into space. While astronauts live and work in orbit on the International Space Station, the only other body in space that humans have walked on is Earth's Moon. So far, humans have only explored to just past the edge of own solar system with space craft and probes. Scientists have used telescopes to observe much farther into space. However, the percent of known space that humans have observed with telescopes and other instruments is difficult to estimate. Scientists estimate that the radius of the universe could be as large as 46.5 billion years, so the distance into space humans can currently observe would represent a little less than one-third of the total distance. However, evidence from gravitational interactions suggests that observable matter and energy, such as stars and the light they produce, make up only a small fraction of the total mass and energy of the universe. Scientists have not yet been able to observe this "dark matter" and "dark energy" which may account for as much as 96% of the universe.