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For the giant planets, the "radius" is defined as the distance from the center at which the atmosphere reaches 1 bar of atmospheric pressure. [11] Because Sedna and 2002 MS 4 have no known moons, directly determining their mass is impossible without sending a probe (estimated to be from 1.7x10 21 to 6.1×10 21 kg for Sedna [12]).
A theoretical planet that may form via mass loss from a low-mass white dwarf. Helium planets are predicted to have roughly the same diameter as hydrogen–helium planets of the same mass. Hycean planet: A hypothetical type of habitable planet described as a hot, water-covered planet with a hydrogen-rich atmosphere. TOI-270 d, K2-18b (candidates)
The choice of solar mass, M ☉, as the basic unit for planetary mass comes directly from the calculations used to determine planetary mass.In the most precise case, that of the Earth itself, the mass is known in terms of solar masses to twelve significant figures: the same mass, in terms of kilograms or other Earth-based units, is only known to five significant figures, which is less than a ...
The four outer planets, called giant planets or Jovian planets, collectively make up 99% of the mass orbiting the Sun. [h] All four giant planets have multiple moons and a ring system, although only Saturn's rings are easily observed from Earth. [91]
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.
Up to a certain mass, an object can be irregular in shape, but beyond that point, which varies depending on the chemical makeup of the object, gravity begins to pull an object towards its own centre of mass until the object collapses into a sphere. [98] Mass is the prime attribute by which planets are distinguished from stars.
Euler diagram showing the types of bodies orbiting the Sun. The following is a list of Solar System objects by orbit, ordered by increasing distance from the Sun.Most named objects in this list have a diameter of 500 km or more.
These are lists of planets.A planet is a large, rounded astronomical body that is neither a star nor its remnant. The best available theory of planet formation is the nebular hypothesis, which posits that an interstellar cloud collapses out of a nebula to create a young protostar orbited by a protoplanetary disk.