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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]).
Kepler-37e is listed with a radius of 0.37 ± 0.18 R 🜨 in the Exoplanet Archive based on KOI data, but the existence of this planet is doubtful, [22] and assuming its existence, a 2023 study found a mass of 8.1 ± 1.7 M 🜨, inconsistent with such a small radius.
The number of dwarf planets in the Solar System is unknown. Estimates have run as high as 200 in the Kuiper belt [1] and over 10,000 in the region beyond. [2] However, consideration of the surprisingly low densities of many large trans-Neptunian objects, as well as spectroscopic analysis of their surfaces, suggests that the number of dwarf planets may be much lower, perhaps only nine among ...
Of the Solar System's eight planets and its nine most likely dwarf planets, six planets and seven dwarf planets are known to be orbited by at least 300 natural satellites, or moons. At least 19 of them are large enough to be gravitationally rounded; of these, all are covered by a crust of ice except for Earth's Moon and Jupiter's Io . [ 1 ]
Candidate planets around Luyten 726-8 (8.77 ly) [115] and GJ 3378 (25.2 ly) were reported in 2024. [77] The Working Group on Extrasolar Planets of the International Astronomical Union adopted in 2003 a working definition on the upper limit for what constitutes a planet: not being massive enough to sustain thermonuclear fusion of deuterium.
The following is a list of numbered minor planets (essentially the same as asteroids) in ascending numerical order. Minor planets are defined as small bodies in the Solar System, including asteroids, distant objects, and dwarf planets, but not including comets. The catalog consists of hundreds of pages, each containing 1,000 minor planets.
Flyby; discovered Selam; smallest main-belt asteroid to be visited by a spacecraft [9] [10] Notes: a A minor planet's dimensions may be described by x, y, and z axes instead of an (average) diameter due to its non-spherical, irregular shape. b Closest approach given in multiples of the minor planet's mean radius
The smallest known extrasolar planet that might be a gas dwarf is Kepler-138d, which is less massive than Earth but has a 60% larger volume and therefore has a density 2.1 +2.2 −1.2 g/cm 3 that indicates either a substantial water content [ 19 ] or possibly a thick gas envelope. [ 20 ]