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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. Planets grow in this disk by the gradual accumulation of material driven by gravity, a process called accretion. The Solar System has at least eight planets: the terrestrial planets Mercury, Venus, Earth and Mars, and the giant planets Jupiter, Saturn, Uranus and Neptune. These planets each rotate around an axis tilted with respect to its orbital pole. All planets of the Solar System other than Mercury possess a considerable atmosphere, and some share such features as ice caps, seasons, volcanism, hurricanes, tectonics, and even hydrology. Apart from Venus and Mars, the Solar System planets generate magnetic fields, and all except Venus and Mercury have natural satellites. The giant planets bear planetary rings, the most prominent being those of Saturn.
The Solar System is the gravitationally bound system of the Sun and the objects that orbit it. It formed 4.6 billion years ago from the gravitational collapse of a giant interstellar molecular cloud. The vast majority (99.86%) of the system's mass is in the Sun, with most of the remaining mass contained in the planet Jupiter. The planetary system around the Sun contains eight planets. The four inner system planets—Mercury, Venus, Earth and Mars—are terrestrial planets, being composed primarily of rock and metal. The four giant planets of the outer system are substantially larger and more massive than the terrestrials. The two largest, Jupiter and Saturn, are gas giants, being composed mainly of hydrogen and helium; the next two, Uranus and Neptune, are ice giants, being composed mostly of volatile substances with relatively high melting points compared with hydrogen and helium, such as water, ammonia, and methane. All eight planets have nearly circular orbits that lie near the plane of Earth's orbit, called the ecliptic.
Pallas is the second asteroid to have been discovered, after Ceres. It is believed to have a mineral composition similar to carbonaceous chondrite meteorites, like Ceres, though significantly less hydrated than Ceres. It is the third-largest asteroid in the Solar System by both volume and mass, and is a likely remnant protoplanet. It is 79% the mass of Vesta and 22% the mass of Ceres, constituting an estimated 7% of the mass of the asteroid belt. Its estimated volume is equivalent to a sphere 507 to 515 kilometers in diameter, 90–95% the volume of Vesta.
The asteroid belt is a torus-shaped region in the Solar System, centered on the Sun and roughly spanning the space between the orbits of the planets Jupiter and Mars. It contains a great many solid, irregularly shaped bodies called asteroids or minor planets. The identified objects are of many sizes, but much smaller than planets, and on average are about one million kilometers apart. This asteroid belt is also called the main asteroid belt or main belt to distinguish it from other asteroid populations in the Solar System.
Brett James Gladman is a Canadian astronomer and a full professor at the University of British Columbia's Department of Physics and Astronomy in Vancouver, British Columbia. He holds the Canada Research Chair in planetary astronomy. He does both theoretical work and observational optical astronomy.
David Clifford Jewitt is a British-American astronomer who studies the Solar System, especially its minor bodies. He is based at the University of California, Los Angeles, where he is a Member of the Institute for Geophysics and Planetary Physics, the Director of the Institute for Planets and Exoplanets, Professor of Astronomy in the Department of Physics and Astronomy and Professor of Astronomy in the Department of Earth, Planetary and Space Sciences. He is best known for being the first person to discover a body beyond Pluto and Charon in the Kuiper belt.
An asteroid family is a population of asteroids that share similar proper orbital elements, such as semimajor axis, eccentricity, and orbital inclination. The members of the families are thought to be fragments of past asteroid collisions. An asteroid family is a more specific term than asteroid group whose members, while sharing some broad orbital characteristics, may be otherwise unrelated to each other.
The interplanetary dust cloud, or zodiacal cloud, consists of cosmic dust that pervades the space between planets within planetary systems, such as the Solar System. This system of particles has been studied for many years in order to understand its nature, origin, and relationship to larger bodies. There are several methods to obtain space dust measurement.
Dermott's law is an empirical formula for the orbital period of major satellites orbiting planets in the Solar System. It was identified by the celestial mechanics researcher Stanley Dermott in the 1960s and takes the form:
The formation of the Solar System began about 4.6 billion years ago with the gravitational collapse of a small part of a giant molecular cloud. Most of the collapsing mass collected in the center, forming the Sun, while the rest flattened into a protoplanetary disk out of which the planets, moons, asteroids, and other small Solar System bodies formed.
Julio Ángel Fernández Alves is a Uruguayan astronomer and teacher, member of the department of astronomy at the Universidad de la República in Montevideo. He is also a member of PEDECIBA,, and the Uruguayan Society of Astronomy. From 2005 to 2010, he was the Dean of the Universidad de la Republica's Faculty of Sciences. The asteroid 5996 Julioangel, discovered in 1983, was named after him.
The Mars trojans are a group of trojan objects that share the orbit of the planet Mars around the Sun. They can be found around the two Lagrangian points 60° ahead of and behind Mars. The origin of the Mars trojans is not well understood. One theory suggests that they were primordial objects left over from the formation of Mars that were captured in its Lagrangian points as the Solar System was forming. However, spectral studies of the Mars trojans indicate this may not be the case. Another explanation involves asteroids chaotically wandering into the Mars Lagrangian points later in the Solar System's formation. This is also questionable considering the short dynamical lifetimes of these objects. The spectra of Eureka and two other Mars trojans indicates an olivine-rich composition. Since olivine-rich objects are rare in the asteroid belt it has been suggested that some of the Mars trojans are captured debris from a large orbit-altering impact on Mars when it encountered a planetary embryo.
Discovery and exploration of the Solar System is observation, visitation, and increase in knowledge and understanding of Earth's "cosmic neighborhood". This includes the Sun, Earth and the Moon, the major planets Mercury, Venus, Mars, Jupiter, Saturn, Uranus, and Neptune, their satellites, as well as smaller bodies including comets, asteroids, and dust.
Retrograde motion in astronomy is, in general, orbital or rotational motion of an object in the direction opposite the rotation of its primary, that is, the central object. It may also describe other motions such as precession or nutation of an object's rotational axis. Prograde or direct motion is more normal motion in the same direction as the primary rotates. However, "retrograde" and "prograde" can also refer to an object other than the primary if so described. The direction of rotation is determined by an inertial frame of reference, such as distant fixed stars.
Paolo Farinella was an Italian scientist very active in the field of planetary science and in particular in the study of asteroids and small bodies of the Solar System.
The Late Heavy Bombardment (LHB), or lunar cataclysm, is a hypothesized event thought to have occurred approximately 4.1 to 3.8 billion years (Ga) ago, at a time corresponding to the Neohadean and Eoarchean eras on Earth. According to the hypothesis, during this interval, a disproportionately large number of asteroids and comets collided with the early terrestrial planets in the inner Solar System, including Mercury, Venus, Earth and Mars. These came from both post-accretion and planetary instability-driven populations of impactors. Although widely accepted, it remains difficult to prove conclusively.
The five-planet Nice model is a numerical model of the early Solar System that is a revised variation of the Nice model. It begins with five giant planets, the four that exist today plus an additional ice giant between Saturn and Uranus in a chain of mean-motion resonances.
In planetary astronomy, the grand tack hypothesis proposes that Jupiter formed at a distance of 3.5 AU from the Sun, then migrated inward to 1.5 AU, before reversing course due to capturing Saturn in an orbital resonance, eventually halting near its current orbit at 5.2 AU. The reversal of Jupiter's planetary migration is likened to the path of a sailboat changing directions (tacking) as it travels against the wind.
References
- 1 2 "UFL Department of Astronomy".
- ↑ Dermott, S. F. (1968). "On the origin of commensurabilities in the solar system - II: The orbital period relation". Mon. Not. R. Astron. Soc. 141 (3): 363–376. Bibcode:1968MNRAS.141..363D. doi:10.1093/mnras/141.3.363.
- ↑ Midelis, Jewel (March 19, 2019). "Asteroid Origins". Explore Magazine. Retrieved March 17, 2023.
- ↑ "Stanley F. Dermott, Ph.D. – UFRF Professors" . Retrieved March 17, 2023.
- ↑ "IAU Minor Planet Center". minorplanetcenter.net. Retrieved March 27, 2023.
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