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Mini-Neptune
A Mini-Neptune (sometimes known as a gas dwarf or transitional planet) is a planet less massive than Neptune but resembling Neptune in that it has a thick hydrogen-helium atmosphere, probably with deep layers of ice, rock or liquid oceans (made of water, ammonia, a mixture of both, or heavier volatiles). A gas dwarf is a gas planet with a rocky core that has accumulated a thick envelope of hydrogen, helium, and other Volatile (astrogeology), volatiles, having, as a result, a total radius between 1.7 and 3.9 Earth radii (). The term is used in a three-tier, metallicity-based classification regime for short-period exoplanets, which also includes the rocky, Terrestrial planet, terrestrial-like planets with less than and planets greater than , namely ice giants and gas giants. Properties Theoretical studies of such planets are loosely based on knowledge about Uranus and Neptune. Without a thick atmosphere, they would be classified as an ocean planet instead. An estimated dividing li ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Hycean Planet
A hycean planet ( ) is a Hypothetical astronomical object, hypothetical type of planet with liquid water oceans underneath a hydrogen-rich atmosphere. Definition The term ''hycean'' is a Blend word, portmanteau of ''hydrogen'' and ''ocean''. Due to the presence of extraterrestrial liquid water, hycean planets are regarded as promising candidates for planetary habitability. They are usually considered to be larger and more massive than Earth. As of 2023, there are no confirmed hycean planets, but the Kepler space telescope, Kepler mission detected many candidates. History The term "hycean planet" was coined in 2021 by a team of planet researchers led by Nikku Madhusudhan at the University of Cambridge, as a portmanteau of "hydrogen" and "ocean," used to describe planets that are thought to have large oceans and hydrogen-rich atmospheres. Hycean planets are thought to be common around red dwarf stars, and are considered to be a promising place to search for life beyond Earth. ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Super-Earth
A super-Earth is a type of exoplanet with a mass higher than Earth, but substantially below those of the Solar System's ice giants, Uranus and Neptune, which are 14.5 and 17.1 times Earth's, respectively. The term "super-Earth" refers only to the mass of the planet, and so does not imply anything about the surface conditions or Planetary habitability, habitability. The alternative term "gas dwarfs" may be more accurate for those at the higher end of the mass scale, although "mini-Neptunes" is a more common term. Definition In general, super-Earths are defined by their masses. The term does not imply temperatures, compositions, orbital properties, habitability, or environments. While sources generally agree on an upper bound of 10 Earth masses (~69% of the mass of Uranus, which is the Solar System's giant planet with the least mass), the lower bound varies from 1 or 1.9 to 5, with various other definitions appearing in the popular media. The term "super-Earth" is also used ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Sub-Neptune
The term sub-Neptune can refer to a planet with a smaller radius than Neptune even though it may have a larger mass or to a planet with a smaller mass than Neptune even though it may have a larger radius like a super-puff and both meanings can even be used in the same publication. Neptune-like planets are considerably rarer than sub-Neptune sized planets, despite being only slightly bigger. Edwin S. Kite, Bruce Fegley Jr., Laura Schaefer, Eric B. Ford, 5 Dec 2019 This "radius cliff" separates sub-Neptunes (radii < 3 Earth radii) from Neptunes (radii > 3 Earth radii). This radius cliff is thought to arise because during formation when gas is accreting, the atmospheres of planets that size reach the pressures required to ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Chthonian Planet
Chthonian planets (, sometimes 'cthonian') are a hypothetical class of celestial objects resulting from the stripping away of a gas giant's hydrogen and helium atmosphere and outer layers, which is called hydrodynamic escape. Such atmospheric stripping is a likely result of proximity to a star. The remaining rocky or metallic core would resemble a terrestrial planet in many respects.Hébrard G., Lecavelier Des Étangs A., Vidal-Madjar A., Désert J.-M., Ferlet R. (2003)''Evaporation Rate of Hot Jupiters and Formation of chthonian Planets'' Extrasolar Planets: Today and Tomorrow, ASP Conference Proceedings, Vol. 321, held 30 June – 4 July 2003, Institut d'astrophysique de Paris, France. Edited by Jean-Philippe Beaulieu, Alain Lecavelier des Étangs and Caroline Terquem. Etymology ''Chthon'' (from ) means "earth". The term ''chthonian'' was coined by Guillaume Hébrard et al. and generally refers to Greek chthonic deities from the infernal underground. Possible examples T ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Gas Giant
A gas giant is a giant planet composed mainly of hydrogen and helium. Jupiter and Saturn are the gas giants of the Solar System. The term "gas giant" was originally synonymous with "giant planet". However, in the 1990s, it became known that Uranus and Neptune are a distinct class of giant planets composed mainly of heavier volatile substances (referred to as "Volatile (astrogeology)#Planetary science, ices"). For this reason, Uranus and Neptune are often classified in the separate category of ice giants. Jupiter and Saturn consist mostly of hydrogen and helium, with heavier elements making up between 3 and 13 percent of their mass.The Interior of Jupiter, Guillot et al., in ''Jupiter: The Planet, Satellites and Magnetosphere'', Bagenal et al., editors, Cambridge University Press, 2004 They are thought to have an outer layer of compressed molecular hydrogen surrounding a layer of liquid metallic hydrogen, with a molten rocky core inside. The outermost portion of their hydrogen atmo ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Ice Giant
An ice giant is a giant planet composed mainly of elements heavier than hydrogen and helium, such as oxygen, carbon, nitrogen, and sulfur. There are two ice giants in the Solar System: Uranus and Neptune. In astrophysics and planetary science the term "ice" refers to volatile chemical compounds with freezing points above about 100 K, such as water, ammonia, or methane, with freezing points of 273 K (0 °C), 195 K (−78 °C), and 91 K (−182 °C), respectively. In the 1990s, it was determined that Uranus and Neptune were a distinct class of giant planet, separate from the other giant planets, Jupiter and Saturn, which are gas giants predominantly composed of hydrogen and helium. Neptune and Uranus are now referred to as ''ice giants''. Lacking well-defined solid surfaces, they are primarily composed of gases and liquids. Their constituent compounds were solids when they were primarily incorporated into the planets during their formation, ei ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Hot Neptune
A hot Neptune is a type of giant planet with a mass similar to that of Neptune or Uranus orbiting close to its star, normally within less than 1 AU. The first hot Neptune to be discovered with certainty was Gliese 436 b (Awohali) in 2007, an exoplanet about 33 light years away. Recent observations have revealed a larger potential population of hot Neptunes in the Milky Way than was previously thought. Hot Neptunes may have formed either ''in situ'' or ''ex situ''. General characteristics Because of their close proximity to their parent stars, hot Neptunes have a much greater rate and chance of transiting their star as seen from a farther outlying point, than planets of the same mass in larger orbits. This increases the chances of discovering them by transit-based observation methods. Transiting hot Neptunes include Gliese 436 b (Awohali) and HAT-P-11b. Gliese 436 b was the first hot Neptune to be discovered with certainty in 2007. The exoplanet Mu Arae c (Dulcinea) discove ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Earth Mass
An Earth mass (denoted as ''M''🜨, ''M''♁ or ''M''E, where 🜨 and ♁ are the astronomical symbols for Earth), is a unit of mass equal to the mass of the planet Earth. The current best estimate for the mass of Earth is , with a relative uncertainty of 10−4.The cited value is the recommended value published by the International Astronomical Union in 2009 (se2016 "Selected Astronomical Constants" in ). It is equivalent to an average density of . Using the nearest metric prefix, the Earth mass is approximately six ronnagrams, or 6.0 Rg. The Earth mass is a standard unit of mass in astronomy that is used to indicate the masses of other planets, including rocky terrestrial planets and exoplanets. One Solar mass is close to Earth masses. The Earth mass excludes the mass of the Moon. The mass of the Moon is about 1.2% of that of the Earth, so that the mass of the Earth–Moon system is close to . Most of the mass is accounted for by iron and oxygen (c. 32% each), m ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Ars Technica
''Ars Technica'' is a website covering news and opinions in technology, science, politics, and society, created by Ken Fisher and Jon Stokes in 1998. It publishes news, reviews, and guides on issues such as computer hardware and software, science, technology policy, and video games. ''Ars Technica'' was privately owned until May 2008, when it was sold to Condé Nast Digital, the online division of Condé Nast Publications. Condé Nast purchased the site, along with two others, for $25 million and added it to the company's ''Wired'' Digital group, which also includes '' Wired'' and, formerly, Reddit. The staff mostly works from home and has offices in Boston, Chicago, London, New York City, and San Francisco. The operations of ''Ars Technica'' are funded primarily by advertising, and it has offered a paid subscription service since 2001. History Ken Fisher, who serves as the website's current editor-in-chief, and Jon Stokes created ''Ars Technica'' in 1998. Its purpose was t ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
