Ten Planets: Stories

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In 2016, researchers proposed the possible existence of a ninth planet, for now, dubbed "Planet Nine" or Planet X. The planet is estimated to be about 10 times the mass of Earth and to orbit the sun between 300 and 1,000 times farther than the orbit of the Earth.

The 2006 IAU definition presents some challenges for exoplanets because the language is specific to the Solar System and the criteria of roundness and orbital zone clearance are not presently observable for exoplanets. [69] The IAU working group on extrasolar planets (WGESP) issued a working definition in 2001 and amended it in 2003. [74] In 2018, this definition was reassessed and updated as knowledge of exoplanets increased. [74] The current official working definition of an exoplanet is as follows: [75] Yes, so many! If you had asked anyone just 30 years ago, the answer would have been "we don’t know". But since then we have discovered already more than 5,000 planets orbiting stars other than our sun (so-called exoplanets). And since often we find multiple of them orbiting the same star, we can count about 4,000 other solar systems. Do solar systems move? Green, D. W. E. (13 September 2006). "(134340) Pluto, (136199) Eris, and (136199) Eris I (Dysnomia)" (PDF). IAU Circular. Central Bureau for Astronomical Telegrams, International Astronomical Union. 8747: 1. Bibcode: 2006IAUC.8747....1G. Circular No. 8747. Archived from the original on 24 June 2008 . Retrieved 5 July 2011. Sarma, K. V. (1997). "Astronomy in India". In Selin, Helaine (ed.). Encyclopaedia of the History of Science, Technology, and Medicine in Non-Western Cultures. Kluwer Academic Publishers. p.116. ISBN 0-7923-4066-3.a b c d Basri, Gibor; Brown, Michael E. (2006). "Planetesimals to Brown Dwarfs: What is a Planet?" (PDF). Annual Review of Earth and Planetary Sciences. 34: 193–216. arXiv: astro-ph/0608417. Bibcode: 2006AREPS..34..193B. doi: 10.1146/annurev.earth.34.031405.125058. S2CID 119338327 . Retrieved 4 August 2008. Sean Solomon, Larry Nittler & Brian Anderson, eds. (2018) Mercury: The View after MESSENGER. Cambridge Planetary Science series no. 21, Cambridge University Press, pp. 72–73. The Hubble Space Telescope captured this image of Saturn during its northern hemisphere summer on July 4, 2020. (Image credit: NASA, ESA, A. Simon (Goddard Space Flight Center), M.H. Wong (University of California, Berkeley), and the OPAL Team) The points at which a planet crosses above and below its reference plane are called its ascending and descending nodes. [182] The longitude of the ascending node is the angle between the reference plane's 0 longitude and the planet's ascending node. The argument of periapsis (or perihelion in the Solar System) is the angle between a planet's ascending node and its closest approach to its star. [182]

The heat and pressure eventually became so high that hydrogen atoms began to combine to form helium. The nuclear reactions released vast amounts of energy and our sun was formed.Hermann Hunger, ed. (1992). Astrological reports to Assyrian kings. State Archives of Assyria. Vol.8. Helsinki University Press. ISBN 978-951-570-130-5. The semi-major axis gives the size of the orbit. It is the distance from the midpoint to the longest diameter of its elliptical orbit. This distance is not the same as its apastron, because no planet's orbit has its star at its exact centre. [182] a b c d Chen, Jingjing; Kipping, David (2016). "Probabilistic Forecasting of the Masses and Radii of Other Worlds". The Astrophysical Journal. 834 (1): 17. arXiv: 1603.08614. doi: 10.3847/1538-4357/834/1/17. S2CID 119114880. An artist's depiction of Parker Solar Probe studying the sun. (Image credit: Johns Hopkins University Applied Physics Laboratory) Under this definition, the Solar System is considered to have eight planets. Bodies that fulfill the first two conditions but not the third are classified as dwarf planets, provided they are not natural satellites of other planets. Originally an IAU committee had proposed a definition that would have included a larger number of planets as it did not include (c) as a criterion. [72] After much discussion, it was decided via a vote that those bodies should instead be classified as dwarf planets. [45]

Its swirling clouds are colorful due to different types of trace gases including ammonia ice, ammonium hydrosulfide crystals as well as water ice and vapor. Free-floating objects in young star clusters with masses below the limiting mass for thermonuclear fusion of deuterium are not "planets", but are "sub-brown dwarfs" (or whatever name is most appropriate). [75]

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