These planet sized objects that orbits the sun are too small to be considered as planets with a natural satellite revolving around them. Asteroid belt also has dwarf planets Ceres and Vesta, Ceres is the biggest. Pluto is also a dwarf beyond Neptune.
Pluto was discovered in 1930 and it was considered as the 9th planet but soon with the discovery of its moon Charon it was found that it is one twentieth the size of Mercury. In the 1990s many more objects with size close to Pluto were discovered. In August 2006, with an IAU (International Astronomical Union) resolution that created an official definition for the term “planet”. Photo failed the conditions to be a planet and declared as a dwarf planet.
Natural Satellite – Moons
Just like we have a moon, other planets also have their moons revolving around them. Each is unique with different morphology and geological conditions.
Venus and Mercury have no moon. Mars has two which are Phobos and Deimos. Jupiter has 53 confirmed moons, Ganymede is the biggest moon in the solar system even bigger than planet Mercury ; other moons of Jupiter are Europa, Io, Callisto, etc. Saturn has 53 confirmed moons, Titan, Enceladus, Mimas, Tethys, Hyperion, Rhea are some of them. Uranus and Neptune have 27 and 14 confirmed moons respectively. Miranda, Ariel, Oberon, etc are moons of Uranus and Triton is one of the moons of Neptune.
Comets are frozen rocks with water and gases that are orbiting the sun. Short period comets lie in the Kuiper belt and long periods to be in the oort cloud. Their orbits are largely eccentric with perigee closer to the sun. Their size varies from a kilometer to tens of kilometers. While orbiting when it gets closer to the sun, it heats up and spews water, gas and dust and forms a tail. Some comets contain organic compounds.
A comet can eject out of the solar system, travelling fast enough or runs out of ice, and gases as a result of evaporation after numerous orbits near the sun, becoming small, dark rock that resembles an asteroid. The orbital period of Halley’s Comet is 75 and will reappear in 2061.
Cosmic dust – Solar System Dust
There is so much empty space in the solar system. Along with the empty space there is finely divided particulate matter or dust that exists between the planets. The size ranges from a few molecules to 0.1 mm, above which size they are called meteoroids.
Sources of this dust are larger meteoroids, asteroids, comets and interstellar dust passing through the solar system also they have existed since the formation of planets. They scatter the light from the sun. The density of the dust cloud through which the Earth is traveling is approximately 10−6 dust grains/m3
It is located beyond Neptune’s orbit from 30 AU to 50 AU. It is home to Pluto and other dwarf planets like Eris, Haumea, Makemake, Sedena, Quaoar, etc. These dwarf planets in the Kuiper Belt are also called Trans Neptunian objects.
Like the Asteroid belt it contains small bodies but asteroids are composed of rock and metal, on the other hand due to being so far away from the sun the temperature is very low at the Kuiper belt that the Kuiper Belt Objects (KBO) are composed of frozen gases like methane, ammonia, water and other gases along with rock.