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
In 2006, the International Astronomical Union defined a planet as a body that is in orbit around the sun, has enough mass to establish a round shape, and has cleared other debris from the neighborhood of its orbit. This ruling famously resulted in the demotion of Pluto to dwarf planet status, since Pluto did not have the gravitational influence to clear other bodies from its orbital path.Full Answer >
The lowest temperature on Venus is minus 175 degrees Celsius, found at an atmospheric layer 125 kilometers above the surface of the planet. The planet's average temperature, however, stands at 464 degrees Celsius, making it hotter than Mercury despite being farther away from the sun.Full Answer >
An exoplanet is a planet that orbits a star other than the sun. The first exoplanet found, 51 Pegasi B, was discovered in 1992, and over 800 have been discovered since.Full Answer >
The planet Uranus was discovered on March 13, 1781, by British astronomer William Herschel. While Uranus is visible from Earth with the naked eye under optimal conditions, it was long assumed to be a star due to its dimness and slow orbit.Full Answer >