Planets of our Solar System
Have you ever stopped to marvel at the beauty of our solar system?
The true nature of the cosmos remains a mystery to those who do not tune in to its magical insight and incalculable wisdom. The planets of our solar system join together to compose a harmonic symphony defining the universe as an ever changing single living organism.
Each planet and celestial body is but one instrument in this orchestra, each of which is rich with history through the ages with regard to its meaning and intellectual reference.
To some ancients the precision of the geometry of planetary movements marked the existence of gods and the intentions of mythological overseers.
Our site has teamed up with one of Europe’s top astrological researchers, to provide an insight into the physical nature of each planet and how we may have come about our astrological character definitions. It’s no secret but a little known fact that great men such as Hippocrates and Astrology, Plato and Astrology, Ptolemy and Astrology, Kepler and Astrology and Jung and Astrology all saw the relevant importance of Astrology and the planets toward finding a deeper understanding of how the heavens reflect our own lives.
Planet, a round body in space that orbits a star. To be a planet, a body must be big enough to settle into a rounded shape from the inward pull of its own gravitation. A planet shines by reflecting light and not by releasing nuclear energy the way a star does. Our solar system has eight major planets—Mercury, Venus, Earth, Mars, Jupiter, Saturn, Uranus, and Neptune—and a number of small, dwarf planets, including Eris and Ceres. A planet-like body that revolves around a larger planet is called a satellite or moon rather than a planet. Planets are distinct from asteroids and comets, smaller bodies that also orbit stars.
The study of planets is called planetary science. Areas of research include the composition, structure, and evolution of planets and planetary systems. New discoveries have made scientists rethink the best way to define what objects should be called planets. Important properties that help determine what should be called a planet include the object’s size, its shape, its location, what it is made of, and the way it formed.
Ideas about planets have changed many times in the history of science. For thousands of years, most people thought that planets circled around Earth instead of the Sun. Many people also believed that planets gave off their own light and were made of a substance called ether that was different from ordinary matter found on Earth. The modern understanding of planets began with the pioneering scientists Nicolaus Copernicus and Galileo in the 16th and early 17th centuries. They showed that planets orbit the Sun and are made of ordinary matter like the Earth.
SOLAR SYSTEM PLANETS
Astronomers have changed the count of official planets in our solar system several times. Copernicus counted six planets: Mercury, Venus, Earth, Mars, Jupiter, and Saturn. Using telescopes, astronomers discovered Uranus in 1781 and Neptune in 1846. Pluto was thought to be a planet when it was discovered in 1930.
For most of the 20th century scientists counted nine planets in our solar system: Mercury, Venus, Earth, Mars, Jupiter, Saturn, Uranus, Neptune, and Pluto. Beginning in the 1990s, astronomers began finding additional small Pluto-like bodies in the outer solar system in a region called the Kuiper Belt. One of these so-called Kuiper Belt Objects (KBOs) turned out to be larger than Pluto and so seemed to qualify as the tenth planet in the solar system. Discovered in 2005 and now called Eris, the distant body forced scientists to find a clearer definition of a planet. The responsibility for defining a planet fell to the International Astronomical Union (IAU), a body of astronomers and other scientists that decides on official names for objects in the solar system and beyond.
According to resolutions passed by the IAU in 2006, a “classical planet” orbiting the Sun must have a rounded shape from effects of its own gravity and must be the dominant object in its region of space. To be the dominant object, the planet must have been massive enough for its own gravitation to clear away other objects in the neighborhood of its orbit. Such objects were either drawn into the planet as the planet formed or were sent off into completely different orbits. The IAU now recognizes eight classical planets in our solar system: Mercury, Venus, Earth, Mars, Jupiter, Saturn, Uranus, and Neptune.
The IAU put Pluto in a new category called “dwarf planets.” Like “classical planets,” dwarf planets orbit the Sun and have rounded shapes. However, dwarf planets are not massive enough for their gravity to clear other bodies from the neighborhoods of their orbits. Dwarf planets are found in regions of the solar system that contain swarms of smaller objects. The asteroid belt between Jupiter and Mars is filled with small rocky bodies, while the Kuiper Belt beyond Neptune and much more distant Oort Cloud contain icy comet-like bodies. Official dwarf planets now include Ceres in the asteroid belt and Eris in the Kuiper Belt. More dwarf planets will be formally recognized in the future.
The IAU’s official definitions of “classical planet” and “dwarf planet” are not meant to apply to bodies outside our solar system. The new definitions are also controversial and have met opposition from a large number of astronomers and planetary scientists. Other researchers, however, have supported the downgrading of Pluto to a dwarf planet as recognition of its origin among the comet-like bodies orbiting the Sun beyond Neptune.
Another resolution passed by the IAU in 2006 designated bodies that are smaller than planets and dwarf planets as “small solar system bodies.” Such objects include asteroids and comets. The IAU keeps an official numbered catalog of “minor planets,” which include dwarf planets, Kuiper Belt Objects (KBOs), and asteroids—but not comets—in the solar system.
In addition to the official definitions decided on by the IAU, scientists use a number of other terms for solar system bodies that share some properties with planets. The term planetoid has been used for objects too small to be planets, most commonly asteroids but also some KBOs. Such smaller objects are also sometimes called planetesimals. The term planetesimal is a broad term that can include comets and is widely used to refer to the objects from which planets are thought to form by accretion—the process of collecting together into larger and larger bodies. A forming planet is called a protoplanet. The general term planetary body can refer to both major and minor planets (asteroids, KBOs), as well as to natural satellites (moons) that are similar to planets in composition but orbit around larger planets.
The planets in our solar system are commonly grouped by their composition and their sizes. The major inner planets Mercury, Venus, Earth, and Mars are called terrestrial (meaning “Earth-like”) or rocky planets, referring to a rocky outer crust around a mantle and a core. The major outer planets Jupiter, Saturn, Uranus, and Neptune are called giant planets, referring to their large size—the term Jovian (meaning “Jupiter-like”) planets is also used for such planets. Jupiter and Saturn are also classified as gas giant planets for their massive atmospheres of hydrogen and helium around a rocky core. Uranus and Neptune are classified as ice giant planets, composed mostly of water in the form of a hot, high-pressure slushy solid or “ice” under an atmosphere of hydrogen and helium and surrounding a rocky core. Pluto and other rounded icy bodies in the Kuiper Belt (KBOs) have been called ice dwarfs, referring to their small size and outer layers of solid ice around a rocky core.
PLANETS BEYOND OUR SOLAR SYSTEM
Scientists have long thought that other stars may have planets the way the Sun does. Beginning in the mid-1990s astronomers began finding planets that orbit other stars, thanks to powerful telescopes and computers to analyze data. Known as extrasolar planets or exoplanets, over 200 of these distant planets have been detected. For more information, see Extrasolar Planets.
There is currently no official scientific definition of a planet that includes the known range of extrasolar planets. An upper size limit on exoplanets can be set, however. Bodies that have about 13 times the mass of Jupiter but less than 8 percent the mass of the Sun are called brown dwarfs. Brown dwarfs are considered a kind of failed star. Anything less massive than a brown dwarf might be considered a planet if it orbits a star.
Objects called planemos (short for “planetary mass objects”) are too small to be brown dwarfs and are similar to giant extrasolar planets—except that they float free in space rather than orbiting a star.
Even stranger kinds of planets have been detected orbiting pulsars, a kind of dense neutron star left by supernova explosions. The planets may have formed from debris created in the catastrophic explosion of a massive star. What such planets are made of is not known.
FORMATION OF PLANETS
According to current theories, stars and planets form in different ways. Stars result from the gravitational collapse of a cloud of gas and dust that is drawn in toward a central body that becomes more and more massive until it begins to fuse hydrogen in its core. When a star forms it may be surrounded by a rotating disk of leftover debris made of gas, dust, and ice.
Planets are thought to take shape by accretion (clumping together) of the tiny dust and ice grains in the disk. The objects collect into planetesimals. The planetsimals gradually accumulate into larger and larger bodies that can build into protoplanets that have a spherical shape from the effects of their own gravity. When a planet is large enough to have settled into a rounded shape, it is said to be in hydrostatic equilibrium.
Last updated on February 25, 2018 at 8:55 pm. Word Count: 1651