Internal structure of the MoonHaving a mean density of 3,346.4 kg/m, the Moon is a differentiated body, being composed of a geochemically distinct crust, mantle, and planetary core. This structure is believed to have resulted from the fractional crystallization of a magma ocean shortly after its formation about 4.5 billion years ago. The energy required to melt the outer portion of the Moon is commonly attributed to a giant impact event that is postulated to have formed the Earth-Moon system, and the subsequent reaccretion of material in Ear...
Mercury (planet)Mercury is the first planet from the Sun and the smallest in the Solar System. It is a rocky planet with a trace atmosphere and a surface gravity slightly lower than that of Mars. The surface of Mercury is similar to Earth's Moon, being cratered, with an expansive rupes system generated from thrust faults, and bright ray systems, formed by ejecta. Its largest crater, Caloris Planitia, has a diameter of 1,550 km (960 mi), which is about one-third the diameter of the planet (4,880 km or 3,030 mi). Being the most i...
Accretion (astrophysics)In astrophysics, accretion is the accumulation of matter into a massive object by gravitationally attracting more matter. If the matter is gaseous the result is an accretion disc. Accretion of solid matter such as dust will form larger solid objects. Most astronomical objects, such as galaxies, stars, and planets, are formed by accretion processes. HistoryThe accretion model that Earth and the other terrestrial planets formed from meteoric material was proposed in 1944 by Otto Schmidt, followed by the protoplane...
Solar SystemThe Solar System is the gravitationally bound system of the Sun and the masses that orbit it, most prominently its eight planets, of which Earth is one. The Solar System is an isolated single-star planetary system (not part of a larger star system) within the Milky Way Galaxy. The system formed about 4.6 billion years ago when a dense region of a molecular cloud collapsed, creating the Sun and a protoplanetary disc from which the orbiting bodies assembled. The Sun accounts for 99.86% of the Solar System's total ...
PlanetA planet is a large, rounded astronomical body that is generally required to be in orbit around a star, stellar remnant, or brown dwarf, and is not one itself. The Solar System has eight planets by the most restrictive definition of the term: the terrestrial planets Mercury, Venus, Earth, and Mars, and the giant planets Jupiter, Saturn, Uranus, and Neptune. 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 ...
JupiterJupiter is the fifth planet from the Sun, and the largest in the Solar System. It is a gas giant with a mass nearly 2.5 times that of all the other planets in the Solar System combined and slightly less than one-thousandth the mass of the Sun. The diameter of Jupiter is 11 times that of Earth and a tenth that of the Sun. It orbits the Sun at a distance of 5.20 AU (778.5 Gm), with an orbital period of 11.86 years. Jupiter is the third-brightest natural object in the Earth's night sky, after the Moon and Venus, an...
MoonThe Moon is the only natural satellite of Earth. It orbits Earth at an average distance of 384,399 kilometers (238,854 mi). Because the Moon follows an elliptical path, its distance from Earth varies over the year, ranging from 357,000–407,000 kilometers (222,000–253,000 mi). a distance roughly 30 times the width of Earth. It completes an orbit (lunar month) in relation to Earth and the Sun (synodically) every 29.5 days. The Moon and Earth are bound by gravitational attraction, which is stronger on the sides...
ExoplanetAn exoplanet or extrasolar planet is a planet outside the Solar System. The first confirmed detection of an exoplanet was in 1992 around a pulsar, and the first detection around a main-sequence star was in 1995. A different planet, first detected in 1988, was confirmed in 2003. In 2016, it was recognized that the first possible evidence of an exoplanet had been noted in 1917, a precovery. As of 20 August 2026, there are 6,354 confirmed exoplanets in 4,756 planetary systems, with 1,060 systems having more than on...
HD 149026 bHD 149026 b, also known as Smertrios, is an exoplanet, specifically a hot Jupiter, approximately 250 light-years from the Sun in the constellation of Hercules. Its host star is HD 149026, also named Ogma . The planet orbits the yellow subgiantstarHD 149026 with a 2.8766-day period at a distance of 0.042 AU (3.9 million mi; 6.3 million km), and is notable first as a transiting planet, and second for a small measured radius (relative to mass and incoming heat) that suggests an exceptionally large planetary core. A...
Gas giantA gas giant is a giant planet composed mainly of hydrogen and helium. There are two gas giants in the Solar System: Jupiter and Saturn. The term "gas giant" was originally synonymous with "giant planet". However, starting in the 1970s and continuing into the 1980s, it became increasingly common to classify Uranus and Neptune separately as ice giants, a distinct class of giant planets composed mainly of heavier volatile substances (referred to as "ices"). Jupiter and Saturn consist mostly of hydrogen and helium, ...
Metallic hydrogenMetallic hydrogen is a phase of hydrogen in which it behaves like an electrical conductor. This phase was predicted in 1935 on theoretical grounds by Eugene Wigner and Hillard Bell Huntington. At high pressure and temperatures, metallic hydrogen can exist as a partial liquid rather than a solid. It is thought to appear in large quantities in the hot and gravitationally compressed interiors of Jupiter and Saturn, as well as in some exoplanets.
SeismologySeismology (; from Ancient Greek σεισμός (seismós), meaning 'earthquake', and -λογία (-logía), meaning 'study of') is the scientific study of earthquakes (or generally, quakes) and the generation and propagation of elastic waves through planetary bodies. It also includes studies of the environmental effects of earthquakes such as tsunamis; other seismic sources such as volcanoes, plate tectonics, glaciers, rivers, oceanic microseisms, and the atmosphere; and artificial processes such as explosions....*As an Amazon Associate I earn from qualifying purchases.