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Earth Trojans
An Earth trojan is an asteroid that orbits the Sun in the vicinity of the Earth–Sun Lagrangian points (leading 60°) or (trailing 60°), thus having an orbit similar to Earth's. Only two Earth trojans have so far been discovered. The name Trojan (celestial body), "trojan" was first used in 1906 for the Jupiter trojans, the asteroids that were observed near the Lagrangian points of Jupiter's orbit. Members (leading) * : A 300-metre diameter asteroid, discovered using the Wide-field Infrared Survey Explorer, Wide-field Infrared Survey Explorer (WISE) satellite in January 2010. * : Discovered by the Pan-STARRS survey in December 2020 and later recognized as an Earth trojan in January 2021. (trailing) * No known objects are currently thought to be trojans of Earth. Searches An Earth-based search for objects was conducted in 1994, covering 0.35 square degrees of sky, under poor observing conditions. Received 24 November 1997; revised 13&nbs ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Lagrangian Point
In celestial mechanics, the Lagrange points (; also Lagrangian points or libration points) are points of equilibrium for small-mass objects under the influence of two massive orbiting bodies. Mathematically, this involves the solution of the restricted three-body problem in which two bodies are far more massive than the third. Normally, the two massive bodies exert an unbalanced gravitational force at a point, altering the orbit of whatever is at that point. At the Lagrange points, the gravitational forces of the two large bodies and the centrifugal force balance each other. This can make Lagrange points an excellent location for satellites, as few orbit corrections are needed to maintain the desired orbit. Small objects placed in orbit at Lagrange points are in equilibrium in at least two directions relative to the center of mass of the large bodies. For any combination of two orbital bodies there are five Lagrange points, L1 to L5, all in the orbital plane of the two lar ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Hayabusa2
is an asteroid sample-return mission operated by the Japanese state space agency JAXA. It is a successor to the ''Hayabusa'' mission, which returned asteroid samples for the first time in June 2010. ''Hayabusa2'' was launched on 3 December 2014 and rendezvoused in space with near-Earth asteroid 162173 Ryugu on 27 June 2018. It surveyed the asteroid for a year and a half and took samples. It left the asteroid in November 2019 and returned the samples to Earth on 5 December 2020 UTC. Its mission has now been extended through at least 2031, when it will rendezvous with the small, rapidly-rotating asteroid . ''Hayabusa2'' carries multiple science payloads for remote sensing and sampling, and four small rovers to investigate the asteroid surface and analyze the environmental and geological context of the samples collected. Mission overview Asteroid 162173 Ryugu (formerly designated ) is a primitive carbonaceous near-Earth asteroid. Carbonaceous asteroids are thought to p ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
3753 Cruithne
3753 Cruithne is a Q-type, Aten asteroid in orbit around the Sun in 1:1 orbital resonance with Earth, making it a co-orbital object. It is an asteroid that, relative to Earth, orbits the Sun in a bean-shaped orbit that effectively describes a horseshoe, and that can change into a quasi-satellite orbit. Cruithne does not orbit Earth and at times it is on the other side of the Sun, placing Cruithne well outside of Earth's Hill sphere. Its orbit takes it near the orbit of Mercury and outside the orbit of Mars. Cruithne orbits the Sun in about one Earth year, but it takes 770 years for the series to complete a horseshoe-shaped movement around Earth. The name ''Cruithne'' is from Irish and refers to the early Picts (Old Irish: ''Cruthin'') in the ''Annals of Ulster''Cruithne: Asteroid 3753 . Western Washington University Planetarium ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Libration
In lunar astronomy, libration is the wagging or wavering of the Moon perceived by Earth-bound observers and caused by changes in their perspective. It permits an observer to see slightly different hemispheres of the surface at different times. It is similar in both cause and effect to the changes in the Moon's apparent size due to changes in distance. It is caused by three mechanisms detailed below, two of which cause a relatively tiny physical libration via tidal forces exerted by the Earth. Such true librations are known as well for other moons with locked rotation. The quite different phenomenon of a trojan asteroid's movement has been called ''Trojan libration''; and ''Trojan libration point'' means Lagrangian point. Lunar libration The Moon keeps one hemisphere of itself facing the Earth, due to tidal locking. Therefore, the first view of the far side of the Moon was not possible until the Soviet probe Luna 3 reached the Moon on October 7, 1959, and further lunar exp ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Accretion Disk
An accretion disk is a structure (often a circumstellar disk) formed by diffuse material in orbital motion around a massive central body. The central body is typically a star. Friction, uneven irradiance, magnetohydrodynamic effects, and other forces induce instabilities causing orbiting material in the disk to spiral inward towards the central body. Gravitational and frictional forces compress and raise the temperature of the material, causing the emission of electromagnetic radiation. The frequency range of that radiation depends on the central object's mass. Accretion disks of young stars and protostars radiate in the infrared; those around neutron stars and black holes in the X-ray part of the spectrum. The study of oscillation modes in accretion disks is referred to as diskoseismology. Manifestations Accretion disks are a ubiquitous phenomenon in astrophysics; active galactic nuclei, protoplanetary disks, and gamma ray bursts all involve accretion disks. These disks very ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
The Daily Telegraph
''The Daily Telegraph'', known online and elsewhere as ''The Telegraph'', is a national British daily broadsheet newspaper published in London by Telegraph Media Group and distributed across the United Kingdom and internationally. It was founded by Arthur B. Sleigh in 1855 as ''The Daily Telegraph & Courier''. Considered a newspaper of record over ''The Times'' in the UK in the years up to 1997, ''The Telegraph'' generally has a reputation for high-quality journalism, and has been described as being "one of the world's great titles". The paper's motto, "Was, is, and will be", appears in the editorial pages and has featured in every edition of the newspaper since 19 April 1858. The paper had a circulation of 363,183 in December 2018, descending further until it withdrew from newspaper circulation audits in 2019, having declined almost 80%, from 1.4 million in 1980.United Newspapers PLC and Fleet Holdings PLC', Monopolies and Mergers Commission (1985), pp. 5–16. Its si ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Moon
The Moon is Earth's only natural satellite. It is the fifth largest satellite in the Solar System and the largest and most massive relative to its parent planet, with a diameter about one-quarter that of Earth (comparable to the width of Australia). The Moon is a planetary-mass object with a differentiated rocky body, making it a satellite planet under the geophysical definitions of the term and larger than all known dwarf planets of the Solar System. It lacks any significant atmosphere, hydrosphere, or magnetic field. Its surface gravity is about one-sixth of Earth's at , with Jupiter's moon Io being the only satellite in the Solar System known to have a higher surface gravity and density. The Moon orbits Earth at an average distance of , or about 30 times Earth's diameter. Its gravitational influence is the main driver of Earth's tides and very slowly lengthens Earth's day. The Moon's orbit around Earth has a sidereal period of 27.3 days. During each synodic period ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Giant-impact Hypothesis
The giant-impact hypothesis, sometimes called the Big Splash, or the Theia Impact, suggests that the Moon formed from the ejecta of a collision between the proto-Earth and a Mars-sized planet, approximately 4.5 billion years ago, in the Hadean eon (about 20 to 100 million years after the Solar System coalesced). The colliding body is sometimes called Theia, from the name of the mythical Greek Titan who was the mother of Selene, the goddess of the Moon. Analysis of lunar rocks, published in a 2016 report, suggests that the impact might have been a direct hit, causing a thorough mixing of both parent bodies. The giant-impact hypothesis is currently the favored scientific hypothesis for the formation of the Moon. Supporting evidence includes: * Earth's spin and the Moon's orbit have similar orientations. * The Earth–Moon system contains an anomalously high angular momentum. Meaning, the momentum contained in Earth's rotation, the Moon's rotation, and the Moon revolving ar ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Theia (planet)
Theia is a hypothesized ancient planet in the early Solar System that, according to the giant-impact hypothesis, collided with the early Earth around 4.5 billion years ago, with some of the resulting ejected debris gathering to form the Moon. In addition to explaining Earth's large satellite, the Theia hypothesis can also explain why Earth's core is larger than expected for a body its size; Theia's core and mantle fused with Earth's core and mantle. According to one version of the hypothesis, Theia was an Earth trojan about the size of Mars, with a diameter of about . Additional evidence published in 2019 suggests that Theia might have formed in the outer Solar System rather than the inner Solar System, and that much of Earth's water originated on Theia. Name Theia was named after Theia, one of the Titans, who in Greek mythology was the mother of Selene, the goddess of the Moon, which parallels the planet Theia's collision with the early Earth that is theorized to have creat ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Mars
Mars is the fourth planet from the Sun and the second-smallest planet in the Solar System, only being larger than Mercury (planet), Mercury. In the English language, Mars is named for the Mars (mythology), Roman god of war. Mars is a terrestrial planet with a thin atmosphere (less than 1% that of Earth's), and has a crust primarily composed of elements similar to Earth's crust, as well as a core made of iron and nickel. Mars has surface features such as impact craters, valleys, dunes and polar ice caps. It has two small and irregularly shaped moons, Phobos (moon), Phobos and Deimos (moon), Deimos. Some of the most notable surface features on Mars include Olympus Mons, the largest volcano and List of tallest mountains in the Solar System, highest known mountain in the Solar System and Valles Marineris, one of the largest canyons in the Solar System. The North Polar Basin (Mars), Borealis basin in the Northern Hemisphere covers approximately 40% of the planet and may be a la ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Planetary Mass Objects
A planetary-mass object (PMO), planemo, or planetary body is by geophysical definition of celestial objects any celestial object massive enough to achieve hydrostatic equilibrium (to be rounded under its own gravity), but not enough to sustain core fusion like a star. The purpose of this term is to refer to a broader range of celestial objects than the concept of planet, since many objects similar in geophysical terms do not conform to typical expectations for a planet. Planetary-mass objects can be quite distinguished in origin and location. Planetary-mass objects include dwarf planets, planetary-mass satellite or free-floating planemos, which may have been ejected from a system (rogue planets) or formed through cloud-collapse rather than accretion (sometimes called sub-brown dwarfs). Types Planetary-mass satellite The three largest satellites Ganymede, Callisto, and Titan are of similar size or larger than the planet Mercury; these and four more – Io, Moon, Eur ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Planetary Differentiation
In planetary science, planetary differentiation is the process by which the chemical elements of a planetary body accumulate in different areas of that body, due to their physical or chemical behavior (e.g. density and chemical affinities). The process of planetary differentiation is mediated by partial melting with heat from radioactive isotope decay and planetary accretion. Planetary differentiation has occurred on planets, dwarf planets, the asteroid 4 Vesta, and natural satellites (such as the Moon). Physical differentiation Gravitational separation High-density materials tend to sink through lighter materials. This tendency is affected by the relative structural strengths, but such strength is reduced at temperatures where both materials are plastic or molten. Iron, the most common element that is likely to form a very dense molten metal phase, tends to congregate towards planetary interiors. With it, many siderophile elements (i.e. materials that readily alloy with iron) ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
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