Stilbon with its speedy motion, was ruled over by Hermes, messenger of the gods and god of learning and wit. [17] According to the IAU definition, there are eight planets in the Solar System, which are (in increasing distance from the Sun): [1] Mercury, Venus, Earth, Mars, Jupiter, Saturn, Uranus, and Neptune. Jupiter is the largest, at 318 Earth masses, whereas Mercury is the smallest, at 0.055 Earth masses. [151] In the Solar System, this mass is generally less than the mass required for a body to clear its orbit; thus, some objects that are considered "planets" under geophysical definitions are not considered as such under the IAU definition, such as Ceres and Pluto. [3] (In practice, the requirement for hydrostatic equilibrium is universally relaxed to a requirement for rounding and compaction under self-gravity; Mercury is not actually in hydrostatic equilibrium, [59] but is universally included as a planet regardless.) [60] Proponents of such definitions often argue that location should not matter and that planethood should be defined by the intrinsic properties of an object. [3] Bassoons - Cellos can play from this part (though in the first instance they should use their dedicated part). Several planets or dwarf planets in the Solar System (such as Neptune and Pluto) have orbital periods that are in resonance with each other or with smaller bodies. This is common in satellite systems (e.g. the resonance between Io, Europa, and Ganymede around Jupiter, or between Enceladus and Dione around Saturn). All except Mercury and Venus have natural satellites, often called "moons". Earth has one, Mars has two, and the giant planets have numerous moons in complex planetary-type systems. Except for Ceres and Sedna, all the consensus dwarf planets are known to have at least one moon as well. Many moons of the giant planets have features similar to those on the terrestrial planets and dwarf planets, and some have been studied as possible abodes of life (especially Europa and Enceladus). [255] [256] [257] [258] [259]

Trumpet in B♭ | Trombone | 2nd Trombone | Trombone (treble clef) | Horn in F | 2nd Horn in F | Tenor horn/Alto sax in E♭ The composition of Earth's atmosphere is different from the other planets because the various life processes that have transpired on the planet have introduced free molecular oxygen. [236] The atmospheres of Mars and Venus are both dominated by carbon dioxide, but differ drastically in density: the average surface pressure of Mars' atmosphere is less than 1% that of Earth's (too low to allow liquid water to exist), [237] while the average surface pressure of Venus' atmosphere is about 92 times that of Earth's. [238] It is likely that Venus' atmosphere was the result of a runaway greenhouse effect in its history, which today makes it the hottest planet by surface temperature, hotter even than Mercury. [239] Despite hostile surface conditions, temperature, and pressure at about 50–55km altitude in Venus' atmosphere are close to Earthlike conditions (the only place in the Solar System beyond Earth where this is so), and this region has been suggested as a plausible base for future human exploration. [240] Titan has the only nitrogen-rich planetary atmosphere in the Solar System other than Earth's. Just as Earth's conditions are close to the triple point of water, allowing it to exist in all three states on the planet's surface, so Titan's are to the triple point of methane. [241] a b c d "IAU 2006 General Assembly: Result of the IAU Resolution votes". International Astronomical Union. 2006 . Retrieved 30 December 2009.

The Five Dwarf Planets

Trombones - The trombone part is available in two notations - bass clef at pitch and treble clef (brass band notation). The former part can also be used by cellos (though they have their own dedicated stave too); the latter by euphoniums and baritones (ditto). Flutes - This line can also be played by violins. Because of the range of the flute, violinists attempting this line will find themselves playing in the higher positions. Violins also have their own dedicated part, so it's suggested that that part should have sufficient instruments on it before any are put on the flute line. In 2011, the Kepler Space Telescope team reported the discovery of the first Earth-sized extrasolar planets orbiting a Sun-like star, Kepler-20e and Kepler-20f. [167] [168] [169] Since that time, more than 100 planets have been identified that are approximately the same size as Earth, 20 of which orbit in the habitable zone of their star – the range of orbits where a terrestrial planet could sustain liquid water on its surface, given enough atmospheric pressure. [170] [171] [172] One in five Sun-like stars is thought to have an Earth-sized planet in its habitable zone, which suggests that the nearest would be expected to be within 12 light-years distance from Earth. [c] The frequency of occurrence of such terrestrial planets is one of the variables in the Drake equation, which estimates the number of intelligent, communicating civilizations that exist in the Milky Way. [175] This definition has not been universally used or accepted. In planetary geology, celestial objects have been assessed and defined as planets by geophysical characteristics. Planetary scientists are more interested in planetary geology than dynamics, so they classify planets based on their geological properties. A celestial body may acquire a dynamic (planetary) geology at approximately the mass required for its mantle to become plastic under its own weight. This leads to a state of hydrostatic equilibrium where the body acquires a stable, round shape, which is adopted as the hallmark of planethood by geophysical definitions. For example: [57]

The 2006 IAU definition presents some challenges for exoplanets because the language is specific to the Solar System and the criteria of roundness and orbital zone clearance are not presently observable for exoplanets. [69] The IAU working group on extrasolar planets (WGESP) issued a working definition in 2001 and amended it in 2003. [74] In 2018, this definition was reassessed and updated as knowledge of exoplanets increased. [74] The current official working definition of an exoplanet is as follows: [75] Double planet– A binary system where two planetary-mass objects share an orbital axis external to both Sources: https://solarsystem.nasa.gov/planets/overview/, https://nssdc.gsfc.nasa.gov/planetary/factsheet/ The IAU defines a true planet as a body that circles the sun without being some other object's satellite; is large enough to be rounded by its own gravity (but not so big that it begins to undergo nuclear fusion, like a star); and has "cleared its neighborhood" of most other orbiting bodies.

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The sun accumulated about 99% of the available matter and the remaining material further from the sun formed smaller clumps inside the spinning disk. Some of these clumps gained enough mass that their gravity shaped them into spheres, becoming planets, dwarf planets and moons. Other leftover pieces became asteroids, comets and smaller moons that make up our solar system. Uranus holds the record for the coldest temperature ever measured in the solar system — minus 371.56 degrees F (minus 224.2 degrees C). The average temperature of Uranus is minus 320 degrees Fahrenheit (-195 degrees Celsius).