What makes life in the universe possible? There are many different factors that play into the possibility of life. Out of the billions of galaxies, it’s estimated that only one out of every ten are able to harbor life and only 44 percent of F6-k3 of main sequences stars around our galaxy have the possibility of sustain life (solstation.com). There are certain molecules needed to create and sustain life and only certain stars can harbor life. The possibility of life in the universe has many different factors. Life requires usable energy sources. For organisms on earth, they must be able to metabolize or use these energy sources. The earth organisms are able to assimilate energy from organic and inorganic sources and some are even able to metabolize sunlight and turn it into energy (text book). If earth did not receive sunlight from the sun it would not be able to continue to make the energy needed; this would result in equilibrium and there would no longer be a way for energy to be made. Life also needs carbon for its most basic functions; such as metabolism, reproduction, and evolution (text book). There are other molecules, nitrogen, oxygen, hydrogen, phosphorus, and sulfur to name a few, that play important roles (text book). Without an abundance of hydrogen and oxygen water would not exist. Water plays an important role as a solvent, which allows for chemical reactions to take place (text book). For there to be life there must be a source of energy, a star, and somewhere for life to thrive, such as a planet. There are different types of planets that are thought to be habitable. These planets are: Super-Earths, which are two ties the size of Earth; water worlds, which range in size but have deep oceans and the possibility of habitable land; and Earth-like planets, these planet are found in their host stars habitable zone, have the possibility of liquid water, and range in size from one half the size of the Earth’s mass to double in mass (solstation.com). For a star to be able to have a planet or planets that can harbor life, it must be the right size. The star cannot be too large or it would burn out before life could take hold on the planet; if it were too small it would be too cool and dim for life to be able to start (solstation.com). Stars in the spectral type O, B, or A dwarfs age too fast for the planet to support the development of Earth-like life; other stars may only be able to support earth-like life for a few billion years, which would not be enough time to develop complex life on land. (solstation.com). Stars that are less than half of our suns mass, stars in the spectral type M, tend to tidally lock planets before life can begin and force any (solstation.com). Once a planet is tidally locked it could lead to the destruction of the planets atmosphere. Most spectral type M stars are likely to harm life on the Earth-like planet because they tend to throw out stellar flares (solstation.com). Although the stars must be within the right range, habitable planets must also be within the right range. For planets to be habitable there must be a source of “energy that can sustain metabolism, liquid water, and the conditions on the planet must be favorable for the assembly of complex organic molecules” (Wikipedia.org). There are more than 1800 recorded planets that orbit other stars in the universe, these are called exoplanets; about 1 in 5 sun-like stars have an earth-like planet within the habitable zone (Wikipedia.org). The habitable zone is an area around a star that “planetary-mass objects with sufficient atmospheric pressure” that can support liquid water on the surface (Wikipedia.org). For there to be life on a planet, the conditions must be perfect. The planet must have the right mix of chemicals and an atmosphere all while being close enough to a star for it to provide life-sustaining energy. There are thousands of possible life sustaining planets, but with the technology that we have now we will not be able to know if these plates actually harbor life.