Last week we covered multiple star systems, but what if we added thousands or even millions of stars to the mix? A star cluster. There are different kinds of clusters, though. Open clusters contain hundreds or thousands of stars held together by gravity. They’re young, and evaporate over time, their stars let loose to roam space freely. Globular clusters, on the other hand, are larger, have hundreds of thousands of stars, and are more spherical. They’re very old, a significant fraction of the age of the Universe itself, and that means their stars have less heavy elements in them, are redder, and probably don’t have planets (though we’re not really sure).
The Ship of the Imagination embarks on a journey through space and time to grasp how the autobiography of the Earth is written in its atoms, its oceans, its continents and all living things. Later, American geologist Marie Tharp creates the first true map of Earth's ocean floor, and discovers microscopic life that exists deep beneath the ocean.
Is it possible that there is a hidden planet within our own solar system? New evidence suggests that the fabled Planet X, or Planet 9, may indeed exist… but where? Meet the teams racing to discover and redefine our planetary neighborhood.