Planets and stars differ in their mass, composition and life cycle. Stars are usually structurally simple bodies of high mass that produce energy by way of nuclear fusion of hydrogen into helium. Planets are much smaller, do not generate light and usually orbit stars.Know More
Solar systems form when clouds of gas and dust coalesce into protostellar accretion disks. Most of the mass in such a disk falls toward the center, which provides the mass and energy required to drive the nuclear fusion engine that powers a star throughout its life. Outside the star, small eddies in the accretion disk collapse locally to form small bodies. These small objects grow in size as they collide with one another over millions of years. The largest of these bodies become planets.
Unlike stars, planets can be gaseous or rocky. Some worlds, such as the dwarf planet Pluto, incorporate ice as a major component of their makeup. At the lower size range, dwarf planets can resemble comets, which are formed in ways similar to planets. The largest possible planet would have a mass 75 times that of Jupiter. Above that threshold, the world's mass is sufficient to sustain fusion, and it is, by definition, considered a brown dwarf star.Learn more about Planets
It would be impossible for humans or any other life to live on Jupiter, as the planet is made up primarily of gases almost the all the way to its core. NASA speculates that it might be possible for a very secure spacecraft to visit Jupiter, but it couldn't land, as the planet does not have any solid surfaces.Full Answer >
Earth is unique in that scientists have found the planet to be the only one to have liquid water on its surface, intelligent life forms living on it, a moon that helps regulate surface temperatures, an atmosphere with 21 percent oxygen and plate tectonics, according to Space.com. Scientists believe Earth exists in a "Goldilocks zone" where conditions are just right to support life.Full Answer >
Because Mars with its famous red coloration is readily visible from Earth, it is unknown who first discovered it; NASA lists the planet as "known by the ancients." There are records of its existence as far back as ancient Egypt.Full Answer >
Saturn formed according to one of two models: the core accretion model, which states that planets formed over time through gravitational forces drawing materials together, or the disk instability model, which states that clumps of dust and gas fused together quickly and progressively formed a planet.Full Answer >