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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 ...
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 ] ).
In many cases it is not possible to have an exact value, and an estimated range is instead provided. The coldest and oldest planet directly imaged is Epsilon Indi Ab, which has six times Jupiter's mass, an effective temperature of 275 K, and an age of about 3.5 Ga. This list includes the four members of the multi-planet system that orbit HR 8799.
Five planets are going to be retrograde in the summer of 2024. Here are the dates for Mercury retrograde, Venus retrograde, Saturn retrograde, Neptune retrograde, Pluto retrograde and more.
The nearest such planet was then as close as 12 light-years away [7] [8] but (see below) is now estimated slightly above four light-years away. On August 24, 2016, astronomers announced the discovery of a rocky planet in the habitable zone of Proxima Centauri , the closest star to Earth (not counting the Sun).
Along with the similar orbits of other distant trans-Neptunian objects, the orbit of Leleākūhonua suggests, but does not prove, the existence of a hypothetical Planet Nine in the outer Solar System. [5] [12] As of 2019, the object is inbound 78 AU from the Sun; [9] about two-and-a-half times farther out than Pluto's current location. [13]
Planet c is possibly a potentially habitable Super-Earth but is probably too hot or massive. [55] [56] Mu Arae: Ara: 17 h 44 m 08.70 s: −51° 50′ 02.6″ 5.15: 51: G3IV-V: 1.077: 5704: 6.413: 4: Planet Quijote orbits in the circumstellar habitable zone. However, it is a gas giant, so it itself is uninhabitable although a large moon orbiting ...
Backyard Worlds: Planet 9 is a NASA-funded citizen science project which is part of the Zooniverse web portal. [1] It aims to discover new brown dwarfs, faint objects that are less massive than stars, some of which might be among the nearest neighbors of the Solar System, and might conceivably detect the hypothesized Planet Nine.