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The Solar System is believed to have formed according to the nebular hypothesis, first proposed in 1755 by Immanuel Kant and independently formulated by Pierre-Simon Laplace. [2] This theory holds that 4.6 billion years ago the Solar System formed from the gravitational collapse of a giant molecular cloud. This initial cloud was likely several ...
The orbits of Solar System planets are nearly circular. Compared to many other systems, they have smaller orbital eccentricity. [70] Although there are attempts to explain it partly with a bias in the radial-velocity detection method and partly with long interactions of a quite high number of planets, the exact causes remain undetermined. [70] [74]
Former planets of the Solar System Former planet Discovery Removal Current status Notes The Morning Star [NB 1]: Antiquity: Antiquity: Aspects of Venus "Phosphorus", the Morning Star of Greek antiquity (Eosphorus, the Dawn-Bringer; called "Lucifer" by the Romans), and "Hesperus", the Evening Star (called "Vesper" by the Romans), were later identified as a single planet, Venus (Aphrodite).
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. The Sun, a spectral class G2V main-sequence star; The inner Solar System and the terrestrial planets. 2021 PH27; Mercury. Mercury-crossing minor planets; Venus. Venus-crossing ...
An extrasolar planet in an orbit close to its star (normally less than one astronomical unit away), with a mass similar to that of Uranus or Neptune. Inferior planets: Planets whose orbits lie within the orbit of Earth. [nb 1] Inner planet: A planet in the Solar System that have orbits smaller than the asteroid belt. [nb 2] Outer planet
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]
There are eight planets within the Solar System; planets outside of the solar system are also known as exoplanets. Artist's concept of the potentially habitable exoplanet Kepler-186f. As of 19 December 2024, there are 5,811 confirmed exoplanets in 4,340 planetary systems, with 973 systems having more than one planet. [1]
A terrestrial planet, tellurian planet, telluric planet, or rocky planet, is a planet that is composed primarily of silicate, rocks or metals. Within the Solar System , the terrestrial planets accepted by the IAU are the inner planets closest to the Sun : Mercury , Venus , Earth and Mars .