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
While no specific date can be identified for the discovery of Mars, knowledge of the planet dates back to ancient civilizations. Ancient Romans, Egyptians and Chinese astronomers independently discovered and named the planet.Full Answer >
Neptune has the longest orbital period of any planet within the solar system. The eighth and most distant planet from the sun, it takes Neptune approximately 165 years to complete a single orbit.Full Answer >
There is no evidence of life existing on Venus, and current scientific theories suggest that it is very unlikely that the planet can support life. The planet's high temperature and lack of water are cited as reasons for its hostility to harboring life.Full Answer >
With an average temperature of minus 288 degrees Fahrenheit and frequent, powerful storms throughout the planet, Saturn is not hospitable to life. Unlike most planets in the Milky Way, Saturn derives its heat from its core rather than from the Sun. The planet is known as a gas giant; it is primarily composed of gases, including hydrogen and molecular helium.Full Answer >