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56-549: The membership of the society comprises over 1,000 scientists and amateur enthusiasts from over 52 countries who are interested in a wide range of planetary science topics. Members interests include meteorites , cosmic dust , asteroids and comets , natural satellites , planets , impact events , and the origins of the Solar System . The Meteoritical Society is the organization that records all known meteorites in its Meteoritical Bulletin . The Society also publishes one of

112-484: A magnetosphere around a planet. Early space probes discovered the gross dimensions of the terrestrial magnetic field, which extends about 10 Earth radii towards the Sun. The solar wind , a stream of charged particles, streams out and around the terrestrial magnetic field, and continues behind the magnetic tail, hundreds of Earth radii downstream. Inside the magnetosphere, there are relatively dense regions of solar wind particles,

168-485: A beginning and an end and that a world could be destroyed by collision with another world. Democritus was also a pioneer of mathematics and geometry in particular. According to Archimedes , Democritus was among the first to observe that a cone and pyramid with the same base area and height has one-third the volume of a cylinder or prism respectively, a result which Archimedes states was later proved by Eudoxus of Cnidus . Plutarch also reports that Democritus worked on

224-415: A mountain as tall as, for example, 15 km (9 mi), would develop so much pressure at its base, due to gravity, that the rock there would become plastic , and the mountain would slump back to a height of roughly 10 km (6 mi) in a geologically insignificant time. Some or all of these geologic principles can be applied to other planets besides Earth. For instance on Mars, whose surface gravity

280-417: A passing and partial resemblance to the 19th-century understanding of atomic structure that has led some to regard Democritus as more of a scientist than other Greek philosophers; however, their ideas rested on very different bases. Democritus, along with Leucippus and Epicurus , proposed the earliest views on the shapes and connectivity of atoms. They reasoned that the solidness of the material corresponded to

336-615: A problem involving the cross-section of a cone that Thomas Heath suggests may be an early version of infinitesimal calculus . Democritus thought that the first humans lived an anarchic and animal sort of life, foraging individually and living off the most palatable herbs and the fruit which grew wild on the trees, until fear of wild animals drove them together into societies. He believed that these early people had no language, but that they gradually began to articulate their expressions, establishing symbols for every sort of object, and in this manner came to understand each other. He says that

392-430: A single scientific explanation than become the king of Persia. Although many anecdotes about Democritus' life survive, their authenticity cannot be verified and modern scholars doubt their accuracy. Ancient accounts of his life have claimed that he lived to a very old age, with some writers claiming that he was over a hundred years old at the time of his death. Democritus wrote on ethics as well as physics. Democritus

448-489: A smooth and polished surface" suggested that it and other worlds might appear "just like the face of the Earth itself". Advances in telescope construction and instrumental resolution gradually allowed increased identification of the atmospheric as well as surface details of the planets. The Moon was initially the most heavily studied, due to its proximity to the Earth, as it always exhibited elaborate features on its surface, and

504-456: A strongly interdisciplinary field, which originally grew from astronomy and Earth science , and now incorporates many disciplines, including planetary geology , cosmochemistry , atmospheric science , physics , oceanography , hydrology , theoretical planetary science , glaciology , and exoplanetology . Allied disciplines include space physics , when concerned with the effects of the Sun on

560-496: A void, but simply rejected the argument of Parmenides on the grounds that motion was an observable fact. Therefore, they asserted, there must be a void. Democritus held that originally the universe was composed of nothing but tiny atoms churning in chaos, until they collided together to form larger units—including the earth and everything on it. He surmised that there are many worlds , some growing, some decaying; some with no sun or moon, some with several. He held that every world has

616-555: A wide range of peer reviewed journals . Some planetary scientists work at private research centres and often initiate partnership research tasks. The history of planetary science may be said to have begun with the Ancient Greek philosopher Democritus , who is reported by Hippolytus as saying The ordered worlds are boundless and differ in size, and that in some there is neither sun nor moon, but that in others, both are greater than with us, and yet with others more in number. And that

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672-455: Is also believed to impart some controversial advice such as " It is better not to have any children, for to bring them up well takes great trouble and care, and seeing them grow up badly is the cruellest of all pains ". He also wrote a treatise on the purpose of life and the nature of happiness. He held that " happiness was not to be found in riches but in the goods of the soul and one should not take pleasure in mortal things ". Another saying that

728-642: Is an important transitional zone between the solid planetary surface and the higher rarefied ionizing and radiation belts. Not all planets have atmospheres: their existence depends on the mass of the planet, and the planet's distance from the Sun ;– too distant and frozen atmospheres occur. Besides the four giant planets , three of the four terrestrial planets ( Earth , Venus , and Mars ) have significant atmospheres. Two moons have significant atmospheres: Saturn 's moon Titan and Neptune 's moon Triton . A tenuous atmosphere exists around Mercury . The effects of

784-520: Is an inert solid that excludes other bodies from its volume and interacts with other atoms mechanically. Quantum-mechanical atoms are similar in that their motion can be described by mechanics in addition to their electric, magnetic and quantum interactions. They are different in that they can be split into protons, neutrons, and electrons. The elementary particles are similar to Democritean atoms in that they are indivisible but their collisions are governed purely by quantum physics . Fermions observe

840-497: Is much less, the largest volcano, Olympus Mons , is 27 km (17 mi) high at its peak, a height that could not be maintained on Earth. The Earth geoid is essentially the figure of the Earth abstracted from its topographic features. Therefore, the Mars geoid ( areoid ) is essentially the figure of Mars abstracted from its topographic features. Surveying and mapping are two important fields of application of geodesy. An atmosphere

896-415: Is nothing—but a nothing cannot exist. The Parmenidean position was "You say there is a void; therefore the void is not nothing; therefore there is not the void." The position of Parmenides appeared validated by the observation that where there seems to be nothing there is air, and indeed even where there is not matter there is something , for instance light waves. The atomists agreed that motion required

952-490: Is often attributed to him is " The hopes of the educated were better than the riches of the ignorant ". He also stated that " the cause of sin is ignorance of what is better " which become a central notion later in the Socratic moral thought. Another idea he propounded which was later echoed in the Socratic moral thought was the maxim that " you are better off being wronged than doing wrong ". His other moral notions went contrary to

1008-400: Is the scientific study of planets (including Earth ), celestial bodies (such as moons , asteroids , comets ) and planetary systems (in particular those of the Solar System ) and the processes of their formation. It studies objects ranging in size from micrometeoroids to gas giants , with the aim of determining their composition, dynamics, formation, interrelations and history. It is

1064-641: The Apollo astronauts for the field geology they would encounter on their lunar missions. Overlapping sequences were identified on images taken by the Lunar Orbiter program , and these were used to prepare a lunar stratigraphic column and geological map of the Moon. One of the main problems when generating hypotheses on the formation and evolution of objects in the Solar System is the lack of samples that can be analyzed in

1120-498: The HED meteorites back to a specific asteroid in the main belt, 4 Vesta . The comparatively few known Martian meteorites have provided insight into the geochemical composition of the Martian crust, although the unavoidable lack of information about their points of origin on the diverse Martian surface has meant that they do not provide more detailed constraints on theories of the evolution of

1176-551: The Pauli exclusion principle , which is similar to the Democritean principle that atoms exclude other bodies from their volume. However, bosons do not, with the prime example being the elementary particle photon . The theory of the atomists appears to be more nearly aligned with that of modern science than any other theory of antiquity. However, the similarity with modern concepts of science can be confusing when trying to understand where

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1232-647: The Van Allen radiation belts . Planetary geophysics includes, but is not limited to, seismology and tectonophysics , geophysical fluid dynamics , mineral physics , geodynamics , mathematical geophysics , and geophysical surveying . Planetary geodesy (also known as planetary geodetics) deals with the measurement and representation of the planets of the Solar System, their gravitational fields and geodynamic phenomena ( polar motion in three-dimensional, time-varying space). The science of geodesy has elements of both astrophysics and planetary sciences. The shape of

1288-436: The biosphere , but those meteorites collected in the last few decades from Antarctica are almost entirely pristine. The different types of meteorites that originate from the asteroid belt cover almost all parts of the structure of differentiated bodies: meteorites even exist that come from the core-mantle boundary ( pallasites ). The combination of geochemistry and observational astronomy has also made it possible to trace

1344-451: The gravity fields of the planets to be mapped. For example, in the 1970s, the gravity field disturbances above lunar maria were measured through lunar orbiters, which led to the discovery of concentrations of mass, mascons , beneath the Imbrium, Serenitatis, Crisium, Nectaris and Humorum basins. If a planet's magnetic field is sufficiently strong, its interaction with the solar wind forms

1400-399: The rotation rate of a planet about its axis can be seen in atmospheric streams and currents. Seen from space, these features show as bands and eddies in the cloud system and are particularly visible on Jupiter and Saturn. Exoplanetology studies exoplanets , the planets existing outside our Solar System . Until recently, the means of studying exoplanets have been extremely limited, but with

1456-469: The Earth is to a large extent the result of its rotation, which causes its equatorial bulge , and the competition of geologic processes such as the collision of plates and of vulcanism , resisted by the Earth's gravity field. These principles can be applied to the solid surface of Earth ( orogeny ; Few mountains are higher than 10 km (6 mi), few deep sea trenches deeper than that because quite simply,

1512-506: The Martian lithosphere . As of July 24, 2013, 65 samples of Martian meteorites have been discovered on Earth. Many were found in either Antarctica or the Sahara Desert. During the Apollo era, in the Apollo program , 384 kilograms of lunar samples were collected and transported to the Earth, and three Soviet Luna robots also delivered regolith samples from the Moon. These samples provide

1568-532: The Middle East. The total mass of recognized lunar meteorites is close to 50 kg. Space probes made it possible to collect data in not only the visible light region but in other areas of the electromagnetic spectrum. The planets can be characterized by their force fields: gravity and their magnetic fields, which are studied through geophysics and space physics. Measuring the changes in acceleration experienced by spacecraft as they orbit has allowed fine details of

1624-475: The Solar System and extrasolar planetary systems. Observing exoplanets and determining their physical properties, exoplanetology , is a major area of research besides Solar System studies. Every planet has its own branch. In planetary science, the term geology is used in its broadest sense, to mean the study of the surface and interior parts of planets and moons, from their core to their magnetosphere. The best-known research topics of planetary geology deal with

1680-408: The Sun, or the geomorphology of the surfaces of the terrestrial planets, to give only a few examples. The main comparison that can be made is to features on the Earth, as it is much more accessible and allows a much greater range of measurements to be made. Earth analog studies are particularly common in planetary geology, geomorphology, and also in atmospheric science. The use of terrestrial analogs

1736-425: The astronomy and physics or Earth sciences departments of universities or research centres, though there are several purely planetary science institutes worldwide. Generally, planetary scientists study one of the Earth sciences , astronomy , astrophysics , geophysics , or physics at the graduate level and concentrate their research in planetary science disciplines. There are several major conferences each year, and

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1792-550: The bodies of the Solar System, and astrobiology . There are interrelated observational and theoretical branches of planetary science. Observational research can involve combinations of space exploration , predominantly with robotic spacecraft missions using remote sensing , and comparative, experimental work in Earth-based laboratories . The theoretical component involves considerable computer simulation and mathematical modelling . Planetary scientists are generally located in

1848-410: The current rate of innovation in research technology , exoplanetology has become a rapidly developing subfield of astronomy . Planetary science frequently makes use of the method of comparison to give a greater understanding of the object of study. This can involve comparing the dense atmospheres of Earth and Saturn's moon Titan , the evolution of outer Solar System objects at different distances from

1904-458: The earliest men lived laboriously, having none of the utilities of life; clothing, houses, fire, domestication, and farming were unknown to them. Democritus presents the early period of mankind as one of learning by trial and error, and says that each step slowly led to more discoveries; they took refuge in the caves in winter, stored fruits that could be preserved, and through reason and keenness of mind came to build upon each new idea. Democritus

1960-472: The features on planetary surfaces and reconstructs the history of their formation, inferring the physical processes that acted on the surface. Planetary geomorphology includes the study of several classes of surface features: The history of a planetary surface can be deciphered by mapping features from top to bottom according to their deposition sequence , as first determined on terrestrial strata by Nicolas Steno . For example, stratigraphic mapping prepared

2016-561: The field of natural philosophy . He was known in antiquity as the ‘laughing philosopher’ because of his emphasis on the value of cheerfulness. Democritus was born in Abdera, on the coast of Thrace . He was a polymath and prolific writer, producing nearly eighty treatises on subjects such as poetry, harmony, military tactics, and Babylonian theology. He traveled extensively, visiting Egypt and Persia, but wasn't particularly impressed by these countries. He once remarked that he would rather uncover

2072-407: The hypothesis came from. Classical atomists could not have had an empirical basis for modern concepts of atoms and molecules. The atomistic void hypothesis was a response to the paradoxes of Parmenides and Zeno , the founders of metaphysical logic, who put forth difficult-to-answer arguments in favor of the idea that there can be no movement. They held that any movement would require a void—which

2128-408: The intervals between the ordered worlds are unequal, here more and there less, and that some increase, others flourish and others decay, and here they come into being and there they are eclipsed. But that they are destroyed by colliding with one another. And that some ordered worlds are bare of animals and plants and all water. In more modern times, planetary science began in astronomy, from studies of

2184-403: The laboratory, where a large suite of tools are available, and the full body of knowledge derived from terrestrial geology can be brought to bear. Direct samples from the Moon, asteroids and Mars are present on Earth, removed from their parent bodies, and delivered as meteorites . Some of these have suffered contamination from the oxidising effect of Earth's atmosphere and the infiltration of

2240-615: The most comprehensive record of the composition of any Solar System body besides the Earth. The numbers of lunar meteorites are growing quickly in the last few years – as of April 2008 there are 54 meteorites that have been officially classified as lunar. Eleven of these are from the US Antarctic meteorite collection, 6 are from the Japanese Antarctic meteorite collection and the other 37 are from hot desert localities in Africa, Australia, and

2296-446: The people"; c.  460 – c.  370 BC ) was an Ancient Greek pre-Socratic philosopher from Abdera , primarily remembered today for his formulation of an atomic theory of the universe . Democritus wrote extensively on a wide variety of topics. None of Democritus' original work has survived, except through second-hand references. Many of these references come from Aristotle , who viewed him as an important rival in

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2352-452: The philosopher's oeuvre which had belonged to aesthetics as a discipline, but only fragments of the relevant works are extant; hence of all Democritus writings on these matters, only a small percentage of his thoughts and ideas can be known. Diogenes Laertius attributes several works to Democritus, but none of them have survived in a complete form. A collections of sayings credited to Democritus have been preserved by Stobaeus , as well as

2408-559: The planetary bodies in the near vicinity of the Earth: the Moon , and the two neighboring planets: Venus and Mars . Of these, the Moon was studied first, using methods developed earlier on the Earth. Planetary geology focuses on celestial objects that exhibit a solid surface or have significant solid physical states as part of their structure. Planetary geology applies geology , geophysics and geochemistry to planetary bodies. Geomorphology studies

2464-467: The rate of new discoveries is very high, partly due to the large number of interplanetary spacecraft currently exploring the Solar System. Planetary science studies observational and theoretical astronomy, geology ( astrogeology ), atmospheric science , and an emerging subspecialty in planetary oceans , called planetary oceanography . This is both an observational and a theoretical science. Observational researchers are predominantly concerned with

2520-417: The senses; they are infinite in numbers and come in infinitely many varieties, and they have existed forever and that these atoms are in constant motion in the void or vacuum. The middle-sized objects of everyday life are complexes of atoms that are brought together by random collisions, differing in kind based on the variations among their constituent atoms. For Democritus, the only true realities are atoms and

2576-418: The shape of the atoms involved. Using analogies from humans' sense experiences , he gave a picture or an image of an atom that distinguished them from each other by their shape, their size, and the arrangement of their parts. Moreover, connections were explained by material links in which single atoms were supplied with attachments: some with hooks and eyes, others with balls and sockets. The Democritean atom

2632-474: The study of the small bodies of the Solar System: those that are observed by telescopes, both optical and radio, so that characteristics of these bodies such as shape, spin, surface materials and weathering are determined, and the history of their formation and evolution can be understood. Theoretical planetary astronomy is concerned with dynamics : the application of the principles of celestial mechanics to

2688-495: The technological improvements gradually produced more detailed lunar geological knowledge. In this scientific process, the main instruments were astronomical optical telescopes (and later radio telescopes ) and finally robotic exploratory spacecraft , such as space probes . The Solar System has now been relatively well-studied, and a good overall understanding of the formation and evolution of this planetary system exists. However, there are large numbers of unsolved questions, and

2744-516: The then prevalent views such as his idea that " A good person not only refrains from wrongdoing but does not even want to do wrong. " for the generally held notion back then was that virtue reaches it apex when it triumphs over conflicting human passions. Later Greek historians consider Democritus to have established aesthetics as a subject of investigation and study, as he wrote theoretically on poetry and fine art long before authors such as Aristotle . Specifically, Thrasyllus identified six works in

2800-409: The unresolved planets. In this sense, the original planetary astronomer would be Galileo , who discovered the four largest moons of Jupiter , the mountains on the Moon , and first observed the rings of Saturn , all objects of intense later study. Galileo's study of the lunar mountains in 1609 also began the study of extraterrestrial landscapes: his observation "that the Moon certainly does not possess

2856-434: The vacuum were the beginning of the universe; and that everything else existed only in opinion. (trans. Yonge 1853) He concluded that divisibility of matter comes to an end, and the smallest possible fragments must be bodies with sizes and shapes, although the exact argument for this conclusion of his is not known. The smallest and indivisible bodies he called "atoms." Atoms, Democritus believed, are too small to be detected by

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2912-537: The void. What we perceive as water, fire, plants, or humans are merely combinations of atoms in the void. The sensory qualities we experience are not real; they exist only by convention. Of the mass of atoms, Democritus said, "The more any indivisible exceeds, the heavier it is." However, his exact position on atomic weight is disputed. His exact contributions are difficult to disentangle from those of his mentor Leucippus , as they are often mentioned together in texts. Their speculation on atoms, taken from Leucippus, bears

2968-731: The world's leading planetary science journals, Meteoritics & Planetary Science , and is a cosponsor with the Geochemical Society of the renowned journal Geochimica et Cosmochimica Acta . The Society presents or cosponsors seven awards each year: The Meteoritical Society hosts an annual meeting during the summer, which generally alternates between North America and Europe . It has also held meetings in South Africa , Australia , Brazil , and Japan . The next meeting will be August 13-18, 2023 at UCLA . Planetary science Planetary science (or more rarely, planetology )

3024-542: Was a student of Leucippus . Early sources such as Aristotle and Theophrastus credit Leucippus with creating atomism and sharing its ideas with Democritus, but later sources credit only Democritus, making it hard to distinguish their individual contributions. We have various quotes from Democritus on atoms, one of them being: δοκεῖ δὲ αὐτῶι τάδε· ἀρχὰς εἶναι τῶν ὅλων ἀτόμους καὶ κενόν, τὰ δ'ἀλλα πάντα νενομίσθαι [δοξάζεσθαι]. (Diogenes Laërtius, Democritus, Vol. IX, 44) Now his principal doctrines were these. That atoms and

3080-506: Was eloquent on ethical topics. Some sixty pages of his fragments, as recorded in Diels–Kranz , are devoted to moral counsel. The ethics and politics of Democritus come to us mostly in the form of maxims. In placing the quest for happiness at the center of moral philosophy, he was followed by almost every moralist of antiquity. The most common maxims associated with him are " Accept favours only if you plan to do greater favours in return ", and he

3136-453: Was first described by Gilbert (1886). This non-exhaustive list includes those institutions and universities with major groups of people working in planetary science. Alphabetical order is used. Smaller workshops and conferences on particular fields occur worldwide throughout the year. Democritus Democritus ( / d ɪ ˈ m ɒ k r ɪ t ə s / , dim- OCK -rit-əs ; Greek : Δημόκριτος , Dēmókritos , meaning "chosen of

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