Will We Recognize Extraterrestrial Life When We See It?
The Milky Way is a barred spiral galaxy, one of hundreds of billions in the observable universe. It's also our home. Like other galaxies, the Milky Way is an isolated collection of stars and other material bound together by their common gravity. In addition to the 100 billion to 400 billion stars in our galaxy, a similar number of planets likely exist in the Milky Way  some of them part of solar systems and some floating freely. Between the stars sit innumerable nebulas, which are clouds of gas and dust. The vast majority of the interstellar gas is hydrogen and helium.