& McNeil (1989) listed HD 10647 as their F9 V standard instead. Eta Cassiopeiae A should probably be avoided as a standard star, but maybe as a boundary star, because it was often considered F9 V in Keenan's publications, but G0 V in Morgan's publications. Life cycle F-type stars have a life-cycle similar to G-type stars. They are hydrogen-fusing and will eventually grow into a red giant that fuses helium instead of hydrogen once their supply of hydrogen is depleted. After the helium too runs out, they begin to fuse carbon. When that also runs out, they shed their outer layers, creating a planetary nebula, and leaving behind, at the center of the nebula, a hot white dwarf. These stars remain stable for ~2-4 billion years. In comparison, G-type stars, like the Sun, stay stable for ~10 billion years. Planets Some of the nearest F-type stars known to support planets include Upsilon Andromedae, Tau Boötis, HD 10647, HD 33564, HD 142, HD 60532, and KOI-3010. Habitability Some studies show that there is a possibility that life could also develop on planets that orbit an F-type star. It is estimated that the habitable zone of a relatively hot F0 star would extend from about 2.0 AU to 3.7 AU and between 1.1 and 2.2 AU for a relatively cool F8 star. However, relative to a G-type star the main problems for a hypothetical lifeform in this particular scenario would be the more intense light and the shorter stellar lifespan of the home star. F-type stars are known to emit much higher energy forms of light, such as UV radiation, which in the long term can have a profoundly negative effect on DNA molecules. Studies have shown that, for a hypothetical planet positioned at an equivalent habitable distance from an F-type star as the Earth is from the Sun (this is farther away from the F-type star, inside the habitable zone of a G2-type), and with a similar atmosphere, life on its surface would receive about 2.5 to 7.1 times more damage from UV light compared to that on Earth. Thus, for its native lifeforms to survive, the hypothetical planet would need to have sufficient atmospheric shielding, such as a denser ozone layer in the upper atmosphere. Without a robust ozone layer, life could theoretically develop on the planet's surface, but it would most likely be confined to underwater or underground regions