In the Star Trek universe, a Class M planet is one habitable by humans and similar life forms. Earth, Vulcan, Romulus, and Qo'noS are examples of Class M planets. The planet needs an atmosphere of oxygen and nitrogen, should be close to a stable star, and have fertile soil and a generally pleasant climate. Most planets shown in the franchise are Class M planets; occasionally another alphabetically named class of planet is shown, each hostile to humanoid life in one or more ways. As a story device, this allowed for easy filming without restriction by environmental suits, but Science correspondent Gretchen Vogel called it a "failure of imagination" when thinking about the limits of the zone capable of supporting life. The origin within the fictional universe is implied to be the Vulcan word Minshara.