This artist's conception illustrates a giant planet floating freely without a parent star. Astronomers recently uncovered evidence for such lone worlds, thought to have been booted from developing star systems. The sun may have captured such a planet, which new work shows may reside at the edge of the solar system.
This artist's concept illustrates the preferred model for explaining ALMA observations of Beta Pictoris. At the outer fringes of the system, the gravitational influence of a hypothetical giant planet (bottom left) captures comets into a dense, massive swarm (right) where frequent collisions occur.
This illustration summarizes the almost 14-billion-year-long history of our universe. It shows the main events that occurred between the initial phase of the cosmos %u2014 where its properties were almost uniform and punctuated only by tiny fluctuations %u2014 to the rich variety of cosmic structure that we observe today, ranging from stars and planets to galaxies and galaxy clusters. Image released March 21, 2013.
Scientists have only searched through a tiny fraction of our galaxy, and with the fast advances in technology, we can expect many more interesting discoveries in the future. But for now, check out the handy infographic below, courtesy of Space.com, displaying all known types of alien worlds.