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The sizes and masses of many of the moons of Jupiter and Saturn are fairly well known due to numerous observations and interactions of the Galileo and Cassini orbiters; however, many of the moons with a radius less than ~100 km, such as Jupiter's Himalia, have far less certain masses. [5]
The radii of these objects range over three orders of magnitude, from planetary-mass objects like dwarf planets and some moons to the planets and the Sun. This list does not include small Solar System bodies , but it does include a sample of possible planetary-mass objects whose shapes have yet to be determined.
The remaining objects of the Solar System (including the four terrestrial planets, the dwarf planets, moons, asteroids, and comets) together comprise less than 0.002% of the Solar System's total mass. [h] The Sun is composed of roughly 98% hydrogen and helium, [41] as are Jupiter and Saturn.
The second resolution, 5B, defined dwarf planets as a subtype of planet, as Stern had originally intended, distinguished from the other eight that were to be called "classical planets". Under this arrangement, the twelve planets of the rejected proposal were to be preserved in a distinction between eight classical planets and four dwarf planets.
Determining the length of a single day on a planet is usually pretty easy. You just pick a landmark and wait for it to reach the exact same point twice in its rotation and you have your answer ...
The yellow ellipses represent the orbits of each planet and the dwarf planet Pluto. The terametre (SI symbol: Tm) is a unit of length in the metric system equal to 1 000 000 000 000 meters (10 12 m). To help compare different distances, this section lists lengths starting at 10 12 m (1 Tm or 1 billion km or 6.7 astronomical units).
The outer atmosphere is generally bland and lacking in contrast, although long-lived features can appear. Wind speeds on Saturn can reach 1,800 kilometres per hour (1,100 miles per hour). The planet has a bright and extensive system of rings, composed mainly of ice particles, with a smaller amount of rocky debris and dust.
Additionally, astronomers have found 6 white dwarfs (stars that have exhausted all fusible hydrogen), 21 brown dwarfs, as well as 1 sub-brown dwarf, WISE 0855−0714 (possibly a rogue planet). The closest system is Alpha Centauri , with Proxima Centauri as the closest star in that system, at 4.2465 light-years from Earth.