Pub Date : 2018-09-26DOI: 10.1093/ACREFORE/9780190647926.013.60
I. Šprajc
During the last three millennia before the Spanish Conquest, the peoples living in the central and southern parts of modern Mexico and the northern part of Central America evolved into complex societies with a number of common characteristics that define the cultural area known as Mesoamerica and are expressed in technology, forms of subsistence, government, architecture, religion, and intellectual achievements, including sophisticated astronomical concepts. For the Aztecs, the Maya, and many other Mesoamerican societies, Venus was one of the most important celestial bodies. Not only were they aware that the brightest “star” appearing in certain periods in the pre-dawn sky was identical to the one that at other times was visible in the evening after sunset; they also acquired quite accurate knowledge about the regularities of the planet’s apparent motion. While Venus was assiduously observed and studied, it also inspired various beliefs, in which its morning and evening manifestations had different attributes. Relevant information is provided by archaeological data, prehispanic manuscripts, early Spanish reports, and ethnographically recorded myths that survive among modern communities as remnants of pre-Conquest tradition. The best-known is the malevolent aspect of the morning star, whose first appearances after inferior conjunction were believed to inflict harm on nature and humanity in a number of ways. However, the results of recent studies suggest that the prevalent significance of the morning star was of relatively late and foreign origin. The most important aspect of the symbolism of Venus was its conceptual association with rain and maize, in which the evening star had a prominent role. It has also been shown that these beliefs must have been motivated by some observational facts, particularly by the seasonality of evening star extremes, which approximately delimit the rainy season and the agricultural cycle in Mesoamerica. As revealed by different kinds of evidence, including architectural alignments to these phenomena, Venus was one of the celestial agents responsible for the timely arrival of rains, which conditioned a successful agricultural season. The planet also had an important place in the concepts concerning warfare and sacrifice, but this symbolism seems to have been derived from other ideas that characterize Mesoamerican religion. Human sacrifices were believed necessary for securing rain, agricultural fertility, and a proper functioning of the universe in general. Since the captives obtained in battles were the most common sacrificial victims, the military campaigns were religiously sanctioned, and the Venus-rain-maize associations became involved in sacrificial symbolism and warfare ritual. These ideas became a significant component of political ideology, fostered by rulers who exploited them to satisfy their personal ambitions and secular goals. In sum, the whole conceptual complex surrounding the planet Venus in Mesoameri
{"title":"Venus in Mesoamerica: Rain, Maize, Warfare, and Sacrifice","authors":"I. Šprajc","doi":"10.1093/ACREFORE/9780190647926.013.60","DOIUrl":"https://doi.org/10.1093/ACREFORE/9780190647926.013.60","url":null,"abstract":"During the last three millennia before the Spanish Conquest, the peoples living in the central and southern parts of modern Mexico and the northern part of Central America evolved into complex societies with a number of common characteristics that define the cultural area known as Mesoamerica and are expressed in technology, forms of subsistence, government, architecture, religion, and intellectual achievements, including sophisticated astronomical concepts. For the Aztecs, the Maya, and many other Mesoamerican societies, Venus was one of the most important celestial bodies. Not only were they aware that the brightest “star” appearing in certain periods in the pre-dawn sky was identical to the one that at other times was visible in the evening after sunset; they also acquired quite accurate knowledge about the regularities of the planet’s apparent motion. While Venus was assiduously observed and studied, it also inspired various beliefs, in which its morning and evening manifestations had different attributes. Relevant information is provided by archaeological data, prehispanic manuscripts, early Spanish reports, and ethnographically recorded myths that survive among modern communities as remnants of pre-Conquest tradition.\u0000 The best-known is the malevolent aspect of the morning star, whose first appearances after inferior conjunction were believed to inflict harm on nature and humanity in a number of ways. However, the results of recent studies suggest that the prevalent significance of the morning star was of relatively late and foreign origin. The most important aspect of the symbolism of Venus was its conceptual association with rain and maize, in which the evening star had a prominent role. It has also been shown that these beliefs must have been motivated by some observational facts, particularly by the seasonality of evening star extremes, which approximately delimit the rainy season and the agricultural cycle in Mesoamerica. As revealed by different kinds of evidence, including architectural alignments to these phenomena, Venus was one of the celestial agents responsible for the timely arrival of rains, which conditioned a successful agricultural season. The planet also had an important place in the concepts concerning warfare and sacrifice, but this symbolism seems to have been derived from other ideas that characterize Mesoamerican religion. Human sacrifices were believed necessary for securing rain, agricultural fertility, and a proper functioning of the universe in general. Since the captives obtained in battles were the most common sacrificial victims, the military campaigns were religiously sanctioned, and the Venus-rain-maize associations became involved in sacrificial symbolism and warfare ritual. These ideas became a significant component of political ideology, fostered by rulers who exploited them to satisfy their personal ambitions and secular goals. In sum, the whole conceptual complex surrounding the planet Venus in Mesoameri","PeriodicalId":304611,"journal":{"name":"Oxford Research Encyclopedia of Planetary Science","volume":"46 1","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"2018-09-26","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"129124301","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2018-08-28DOI: 10.1093/acrefore/9780190647926.013.107
R. P. Rajagopalan
Outer space is once again facing renewed competition. Unlike in the earlier decades of space exploration when there were two or three spacefaring powers, by the turn of the 21st century, there are more than 60 players making the outer space environment crowded and congested. Space is no more a domain restricted to state players. Even though it is mostly a western phenomenon, the reality of commercial players as a major actor is creating new dynamics. The changing power transitions are making outer space contested and competitive. Meanwhile, safe and secure access to outer space is being challenged by a number of old and new threats including space debris, militarization of space, radio frequency interference, and potential arms race in space. While a few foundational treaties and legal instruments exist in order to regulate outer space activities, they have become far too expansive to be useful in restricting the current trend that could make outer space inaccessible in the longer term. The need for new rules of the road in the form of norms of responsible behavior, transparency and confidence building measures (TCBMs) such as a code of conduct, a group of governmental experts (GGE), and legal mechanisms, is absolutely essential to have safe, secure, and uninterrupted access to outer space. Current efforts to develop these measures have been fraught with challenges, ranging from agreement on identifying the problems to ideating possible solutions. This is a reflection of the shifting balance of power equations on the one hand, and the proliferation of technology to a large number of players on the other, which makes the decision-making process a lot problematic. In fact, it is the crisis in decision making and the lack of consensus among major space powers that is impeding the process of developing an effective outer space regime.
{"title":"Space Governance","authors":"R. P. Rajagopalan","doi":"10.1093/acrefore/9780190647926.013.107","DOIUrl":"https://doi.org/10.1093/acrefore/9780190647926.013.107","url":null,"abstract":"Outer space is once again facing renewed competition. Unlike in the earlier decades of space exploration when there were two or three spacefaring powers, by the turn of the 21st century, there are more than 60 players making the outer space environment crowded and congested. Space is no more a domain restricted to state players. Even though it is mostly a western phenomenon, the reality of commercial players as a major actor is creating new dynamics. The changing power transitions are making outer space contested and competitive. Meanwhile, safe and secure access to outer space is being challenged by a number of old and new threats including space debris, militarization of space, radio frequency interference, and potential arms race in space. While a few foundational treaties and legal instruments exist in order to regulate outer space activities, they have become far too expansive to be useful in restricting the current trend that could make outer space inaccessible in the longer term. The need for new rules of the road in the form of norms of responsible behavior, transparency and confidence building measures (TCBMs) such as a code of conduct, a group of governmental experts (GGE), and legal mechanisms, is absolutely essential to have safe, secure, and uninterrupted access to outer space. Current efforts to develop these measures have been fraught with challenges, ranging from agreement on identifying the problems to ideating possible solutions. This is a reflection of the shifting balance of power equations on the one hand, and the proliferation of technology to a large number of players on the other, which makes the decision-making process a lot problematic. In fact, it is the crisis in decision making and the lack of consensus among major space powers that is impeding the process of developing an effective outer space regime.","PeriodicalId":304611,"journal":{"name":"Oxford Research Encyclopedia of Planetary Science","volume":"47 1","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"2018-08-28","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"117004243","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2018-08-28DOI: 10.1093/acrefore/9780190647926.013.8
W. Mendell
Emergence of ballistic missile technology after World War II enabled human flight into the Earth’s orbit, fueling the imagination of those fascinated with science, technology, exploration, and adventure. The performance of astronauts in the early flights assuaged concerns about the functioning of “the human system” in the absence of the Earth’s gravity. However, researchers in space medicine have observed degradation of crews after longer exposure to the space environment and have developed countermeasures for most of them, although significant challenges remain. With the dawn of the 21st century, well-financed and technically competent commercial entities have begun to provide more affordable alternatives to historically expensive and risk-averse government-funded programs. The growing accessibility to space has encouraged entrepreneurs to pursue plans for potentially autarkic communities beyond the Earth, exploiting natural resources on other worlds. Should such dreams prove to be technically and economically feasible, a new era will open for humanity with concomitant societal issues of a revolutionary nature.
{"title":"Human Exploration and Development in the Solar System","authors":"W. Mendell","doi":"10.1093/acrefore/9780190647926.013.8","DOIUrl":"https://doi.org/10.1093/acrefore/9780190647926.013.8","url":null,"abstract":"Emergence of ballistic missile technology after World War II enabled human flight into the Earth’s orbit, fueling the imagination of those fascinated with science, technology, exploration, and adventure. The performance of astronauts in the early flights assuaged concerns about the functioning of “the human system” in the absence of the Earth’s gravity. However, researchers in space medicine have observed degradation of crews after longer exposure to the space environment and have developed countermeasures for most of them, although significant challenges remain. With the dawn of the 21st century, well-financed and technically competent commercial entities have begun to provide more affordable alternatives to historically expensive and risk-averse government-funded programs. The growing accessibility to space has encouraged entrepreneurs to pursue plans for potentially autarkic communities beyond the Earth, exploiting natural resources on other worlds. Should such dreams prove to be technically and economically feasible, a new era will open for humanity with concomitant societal issues of a revolutionary nature.","PeriodicalId":304611,"journal":{"name":"Oxford Research Encyclopedia of Planetary Science","volume":"14 1","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"2018-08-28","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"133458793","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2018-08-28DOI: 10.1093/acrefore/9780190647926.013.167
S. Badman
This is an advance summary of a forthcoming article in the Oxford Research Encyclopedia of Planetary Science. Please check back later for the full article. Saturn’s magnetosphere is the region of space surrounding Saturn that is controlled by the planetary magnetic field. Saturn’s magnetic field is aligned to within 1 degree of the rotation axis and rotates with a period of ~10.7 h. The magnetosphere is compressed on the dayside by the impinging solar wind, and stretched into a long magnetotail on the nightside. Its surface, the magnetopause, is located where the internal and external plasma and magnetic pressures balance. As a result of the pressure distributions, the magnetopause has a bimodal distribution of standoff distance at the sub-solar point and is flattened over the poles relative to the equator. Radiation belts composed of trapped energetic electrons and protons are present in the inner magnetosphere. Their intensity is limited by the moons and rings that can absorb the energetic particles. The icy moons and rings, particularly the cryovolcanic moon Enceladus, are the main sources of mass in the form of water. When the water molecules are ionized they are confined to the equatorial plane by the rapidly rotating magnetic field. This mass-loading acts to distend the magnetic field lines from a dipolar configuration into a radially stretched magnetodisk, with an associated eastward-directed current. In situ measurements of plasma velocity indicate it generally lags behind the planetary rotation, introducing an azimuthal component of the magnetic field. Despite the alignment of the magnetic and rotation axes, so-called planetary period oscillations are ubiquitous in field and plasma measurements in the magnetosphere. Radial transport of plasma involves the centrifugal interchange instability in the inner magnetosphere and magnetic reconnection in the middle and outer magnetosphere. This allows mass from the moons and rings to be lost from the system. The outermost regions of the magnetosphere are also influenced by the surrounding solar wind through magnetic reconnection and viscous interactions. Acceleration via reconnection or other processes, or scattering of plasma into the atmosphere leads to auroral emissions detected at radio, infrared, visible, and ultraviolet wavelengths.
{"title":"The Magnetosphere of Saturn","authors":"S. Badman","doi":"10.1093/acrefore/9780190647926.013.167","DOIUrl":"https://doi.org/10.1093/acrefore/9780190647926.013.167","url":null,"abstract":"\u0000 This is an advance summary of a forthcoming article in the Oxford Research Encyclopedia of Planetary Science. Please check back later for the full article.\u0000 \u0000 Saturn’s magnetosphere is the region of space surrounding Saturn that is controlled by the planetary magnetic field. Saturn’s magnetic field is aligned to within 1 degree of the rotation axis and rotates with a period of ~10.7 h. The magnetosphere is compressed on the dayside by the impinging solar wind, and stretched into a long magnetotail on the nightside. Its surface, the magnetopause, is located where the internal and external plasma and magnetic pressures balance. As a result of the pressure distributions, the magnetopause has a bimodal distribution of standoff distance at the sub-solar point and is flattened over the poles relative to the equator.\u0000 Radiation belts composed of trapped energetic electrons and protons are present in the inner magnetosphere. Their intensity is limited by the moons and rings that can absorb the energetic particles. The icy moons and rings, particularly the cryovolcanic moon Enceladus, are the main sources of mass in the form of water. When the water molecules are ionized they are confined to the equatorial plane by the rapidly rotating magnetic field. This mass-loading acts to distend the magnetic field lines from a dipolar configuration into a radially stretched magnetodisk, with an associated eastward-directed current. In situ measurements of plasma velocity indicate it generally lags behind the planetary rotation, introducing an azimuthal component of the magnetic field. Despite the alignment of the magnetic and rotation axes, so-called planetary period oscillations are ubiquitous in field and plasma measurements in the magnetosphere.\u0000 Radial transport of plasma involves the centrifugal interchange instability in the inner magnetosphere and magnetic reconnection in the middle and outer magnetosphere. This allows mass from the moons and rings to be lost from the system. The outermost regions of the magnetosphere are also influenced by the surrounding solar wind through magnetic reconnection and viscous interactions. Acceleration via reconnection or other processes, or scattering of plasma into the atmosphere leads to auroral emissions detected at radio, infrared, visible, and ultraviolet wavelengths.","PeriodicalId":304611,"journal":{"name":"Oxford Research Encyclopedia of Planetary Science","volume":"477 1","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"2018-08-28","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"133535240","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2018-06-25DOI: 10.1093/acrefore/9780190647926.013.128
P. Byrne
Mercury, like its inner Solar System planetary neighbors Venus, Mars, and the Moon, shows no evidence of having ever undergone plate tectonics. Nonetheless, the innermost planet boasts a long record of tectonic deformation. The most prominent manifestation of this history is a population of large scarps that occurs throughout the planet’s cratered terrains; some of these scarps rise kilometers above the surrounding landscape. Mercury’s smooth plains, the majority of which are volcanic and occupy over a quarter of the planet, abound with low-relief ridges. The scarps and ridges are underlain by thrust faults and point to a tectonic history dominated by crustal shortening. At least some of the shortening strain recorded by the ridges may reflect subsidence of the lavas in which they formed, but the widespread distribution of scarps attests to a planetwide process of global contraction, wherein Mercury experienced a reduction in volume as its interior cooled through time. The onset of this phenomenon placed the lithosphere into a net state of horizontal compression, and accounts for why Mercury hosts only a few instances of extensional structures. These landforms, shallow troughs that form complex networks, occur almost wholly in volcanically flooded impact craters and basins and developed as those lavas cooled and thermally contracted. Tellingly, widespread volcanism on Mercury ended at around the same time the population of scarps began to form. Explosive volcanism endured beyond this point, but almost exclusively at sites of lithospheric weakness, where large faults penetrate deep into the interior. These observations are consistent with decades-old predictions that global contraction would shut off major volcanic activity, and illustrate how closely Mercury’s tectonic and volcanic histories are intertwined. The tectonic character of Mercury is thus one of sustained crustal shortening with only localized extension, which started almost four billion years ago and extends into the geologically recent past. This character somewhat resembles that of the Moon, but differs substantially from those of Earth, Venus, or Mars. Mercury may represent how small rocky planets tectonically evolve and could provide a basis for understanding the geological properties of similarly small worlds in orbit around other stars.
{"title":"Tectonism of Mercury","authors":"P. Byrne","doi":"10.1093/acrefore/9780190647926.013.128","DOIUrl":"https://doi.org/10.1093/acrefore/9780190647926.013.128","url":null,"abstract":"Mercury, like its inner Solar System planetary neighbors Venus, Mars, and the Moon, shows no evidence of having ever undergone plate tectonics. Nonetheless, the innermost planet boasts a long record of tectonic deformation. The most prominent manifestation of this history is a population of large scarps that occurs throughout the planet’s cratered terrains; some of these scarps rise kilometers above the surrounding landscape. Mercury’s smooth plains, the majority of which are volcanic and occupy over a quarter of the planet, abound with low-relief ridges. The scarps and ridges are underlain by thrust faults and point to a tectonic history dominated by crustal shortening. At least some of the shortening strain recorded by the ridges may reflect subsidence of the lavas in which they formed, but the widespread distribution of scarps attests to a planetwide process of global contraction, wherein Mercury experienced a reduction in volume as its interior cooled through time.\u0000 The onset of this phenomenon placed the lithosphere into a net state of horizontal compression, and accounts for why Mercury hosts only a few instances of extensional structures. These landforms, shallow troughs that form complex networks, occur almost wholly in volcanically flooded impact craters and basins and developed as those lavas cooled and thermally contracted. Tellingly, widespread volcanism on Mercury ended at around the same time the population of scarps began to form. Explosive volcanism endured beyond this point, but almost exclusively at sites of lithospheric weakness, where large faults penetrate deep into the interior. These observations are consistent with decades-old predictions that global contraction would shut off major volcanic activity, and illustrate how closely Mercury’s tectonic and volcanic histories are intertwined.\u0000 The tectonic character of Mercury is thus one of sustained crustal shortening with only localized extension, which started almost four billion years ago and extends into the geologically recent past. This character somewhat resembles that of the Moon, but differs substantially from those of Earth, Venus, or Mars. Mercury may represent how small rocky planets tectonically evolve and could provide a basis for understanding the geological properties of similarly small worlds in orbit around other stars.","PeriodicalId":304611,"journal":{"name":"Oxford Research Encyclopedia of Planetary Science","volume":"27 1","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"2018-06-25","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"121258802","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2018-06-25DOI: 10.1093/ACREFORE/9780190647926.013.166
Xin Cao, C. Paty
This is an advance summary of a forthcoming article in the Oxford Research Encyclopedia of Planetary Science. Please check back later for the full article. A magnetosphere is formed by the interaction between the magnetic field of a planet and the high-speed solar wind. Those planets with a magnetosphere have an intrinsic magnetic field such as Earth, Jupiter, and Saturn. Mars, especially, has no global magnetosphere, but evidence shows that a paleo-magnetosphere existed billions of years ago and was dampened then due to some reasons such as the change of internal activity. A magnetosphere is very important for the habitable environment of a planet because it provides the foremost and only protection for the planet from the energetic solar wind radiation. The majority of planets with a magnetosphere in our solar system have been studied for decades except for Uranus and Neptune, which are known as ice giant planets. This is because they are too far away from us (about 19 AU from the Sun), which means they are very difficult to directly detect. Compared to many other space detections to other planets, for example, Mars, Jupiter, Saturn and some of their moons, the only single fly-by measurement was made by the Voyager 2 spacecraft in the 1980s. The data it sent back to us showed that Uranus has a very unusual magnetosphere, which indicated that Uranus has a very large obliquity, which means its rotational axis is about 97.9° away from the north direction, with a relative rapid (17.24 hours) daily rotation. Besides, the magnetic axis is tilted 59° away from its rotational axis, and the magnetic dipole of the planet is off center, shifting 1/3 radii of Uranus toward its geometric south pole. Due to these special geometric and magnetic structures, Uranus has an extremely dynamic and asymmetric magnetosphere. Some remote observations revealed that the aurora emission from the surface of Uranus distributed at low latitude locations, which has rarely happened on other planets. Meanwhile, it indicated that solar wind plays a significant impact on the surface of Uranus even if the distance from the Sun is much farther than that of many other planets. A recent study, using numerical simulation, showed that Uranus has a “Switch-like” magnetosphere that allows its global magnetosphere to open and close periodically with the planetary rotation. In this article, we will review the historic studies of Uranus’s magnetosphere and then summarize the current progress in this field. Specifically, we will discuss the Voyager 2 spacecraft measurement, the ground-based and space-based observations such as Hubble Space Telescope, and the cutting-edge numerical simulations on it. We believe that the current progress provides important scientific context to boost future ice giant detection.
{"title":"The Magnetosphere of Uranus","authors":"Xin Cao, C. Paty","doi":"10.1093/ACREFORE/9780190647926.013.166","DOIUrl":"https://doi.org/10.1093/ACREFORE/9780190647926.013.166","url":null,"abstract":"\u0000 This is an advance summary of a forthcoming article in the Oxford Research Encyclopedia of Planetary Science. Please check back later for the full article.\u0000 \u0000 A magnetosphere is formed by the interaction between the magnetic field of a planet and the high-speed solar wind. Those planets with a magnetosphere have an intrinsic magnetic field such as Earth, Jupiter, and Saturn. Mars, especially, has no global magnetosphere, but evidence shows that a paleo-magnetosphere existed billions of years ago and was dampened then due to some reasons such as the change of internal activity. A magnetosphere is very important for the habitable environment of a planet because it provides the foremost and only protection for the planet from the energetic solar wind radiation.\u0000 The majority of planets with a magnetosphere in our solar system have been studied for decades except for Uranus and Neptune, which are known as ice giant planets. This is because they are too far away from us (about 19 AU from the Sun), which means they are very difficult to directly detect. Compared to many other space detections to other planets, for example, Mars, Jupiter, Saturn and some of their moons, the only single fly-by measurement was made by the Voyager 2 spacecraft in the 1980s. The data it sent back to us showed that Uranus has a very unusual magnetosphere, which indicated that Uranus has a very large obliquity, which means its rotational axis is about 97.9° away from the north direction, with a relative rapid (17.24 hours) daily rotation. Besides, the magnetic axis is tilted 59° away from its rotational axis, and the magnetic dipole of the planet is off center, shifting 1/3 radii of Uranus toward its geometric south pole. Due to these special geometric and magnetic structures, Uranus has an extremely dynamic and asymmetric magnetosphere.\u0000 Some remote observations revealed that the aurora emission from the surface of Uranus distributed at low latitude locations, which has rarely happened on other planets. Meanwhile, it indicated that solar wind plays a significant impact on the surface of Uranus even if the distance from the Sun is much farther than that of many other planets. A recent study, using numerical simulation, showed that Uranus has a “Switch-like” magnetosphere that allows its global magnetosphere to open and close periodically with the planetary rotation.\u0000 In this article, we will review the historic studies of Uranus’s magnetosphere and then summarize the current progress in this field. Specifically, we will discuss the Voyager 2 spacecraft measurement, the ground-based and space-based observations such as Hubble Space Telescope, and the cutting-edge numerical simulations on it. We believe that the current progress provides important scientific context to boost future ice giant detection.","PeriodicalId":304611,"journal":{"name":"Oxford Research Encyclopedia of Planetary Science","volume":"61 1","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"2018-06-25","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"130303975","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2018-06-25DOI: 10.1093/ACREFORE/9780190647926.013.73
P. Blount
The use and exploration of space by humans is historically implicated with international and national security. Space exploration itself was sparked, in part, by the race to develop intercontinental ballistic missiles (ICBM), and the strategic uses of space enable the global projection of force by major military powers. The recognition of space as a strategic domain spurred states to develop the initial laws and policies that govern space activities to reduce the likelihood of conflict. Space security, therefore, is a foundational concept to space law. Since the beginning of the Space Age, the concept of security has morphed into a multivariate term, and contemporary space security concerns more than just securing states from the dangers of ICBMs. The prevalence of space technologies across society means that security issues connected to the space domain touch on a range of legal regimes. Specifically, space security law involves components of international peace and security, national security, human security, and the security of the space environment itself.
{"title":"Space Security Law","authors":"P. Blount","doi":"10.1093/ACREFORE/9780190647926.013.73","DOIUrl":"https://doi.org/10.1093/ACREFORE/9780190647926.013.73","url":null,"abstract":"The use and exploration of space by humans is historically implicated with international and national security. Space exploration itself was sparked, in part, by the race to develop intercontinental ballistic missiles (ICBM), and the strategic uses of space enable the global projection of force by major military powers. The recognition of space as a strategic domain spurred states to develop the initial laws and policies that govern space activities to reduce the likelihood of conflict. Space security, therefore, is a foundational concept to space law.\u0000 Since the beginning of the Space Age, the concept of security has morphed into a multivariate term, and contemporary space security concerns more than just securing states from the dangers of ICBMs. The prevalence of space technologies across society means that security issues connected to the space domain touch on a range of legal regimes. Specifically, space security law involves components of international peace and security, national security, human security, and the security of the space environment itself.","PeriodicalId":304611,"journal":{"name":"Oxford Research Encyclopedia of Planetary Science","volume":"21 1","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"2018-06-25","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"132491567","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2018-06-25DOI: 10.1093/acrefore/9780190647926.013.29
F. Nimmo
This article consists of three sections. The first discusses how we determine satellite internal structures and what we know about them. The primary probes of internal structure are measurements of magnetic induction, gravity, and topography, as well as rotation state and orientation. Enceladus, Europa, Ganymede, Callisto, Titan, and (perhaps) Pluto all have subsurface oceans; Callisto and Titan may be only incompletely differentiated. The second section describes dynamical processes that affect satellite interiors and surfaces: tidal and radioactive heating, flexure and relaxation, convection, cryovolcanism, true polar wander, non-synchronous rotation, orbital evolution, and impacts. The final section discusses how the satellites formed and evolved. Ancient tidal heating episodes and subsequent refreezing of a subsurface ocean are the likeliest explanation for the deformation observed at Ganymede, Tethys, Dione, Rhea, Miranda, Ariel, and Titania. The high heat output of Enceladus is a consequence of Saturn’s highly dissipative interior, but the dissipation rate is strongly frequency-dependent and does not necessarily imply that Saturn’s moons are young. Major remaining questions include the origins of Titan’s atmosphere and high eccentricity, the regular density progression in the Galilean satellites, and the orbital evolution of the Saturnian and Uranian moons.
{"title":"Icy Satellites: Interior Structure, Dynamics, and Evolution","authors":"F. Nimmo","doi":"10.1093/acrefore/9780190647926.013.29","DOIUrl":"https://doi.org/10.1093/acrefore/9780190647926.013.29","url":null,"abstract":"This article consists of three sections. The first discusses how we determine satellite internal structures and what we know about them. The primary probes of internal structure are measurements of magnetic induction, gravity, and topography, as well as rotation state and orientation. Enceladus, Europa, Ganymede, Callisto, Titan, and (perhaps) Pluto all have subsurface oceans; Callisto and Titan may be only incompletely differentiated. The second section describes dynamical processes that affect satellite interiors and surfaces: tidal and radioactive heating, flexure and relaxation, convection, cryovolcanism, true polar wander, non-synchronous rotation, orbital evolution, and impacts. The final section discusses how the satellites formed and evolved. Ancient tidal heating episodes and subsequent refreezing of a subsurface ocean are the likeliest explanation for the deformation observed at Ganymede, Tethys, Dione, Rhea, Miranda, Ariel, and Titania. The high heat output of Enceladus is a consequence of Saturn’s highly dissipative interior, but the dissipation rate is strongly frequency-dependent and does not necessarily imply that Saturn’s moons are young. Major remaining questions include the origins of Titan’s atmosphere and high eccentricity, the regular density progression in the Galilean satellites, and the orbital evolution of the Saturnian and Uranian moons.","PeriodicalId":304611,"journal":{"name":"Oxford Research Encyclopedia of Planetary Science","volume":"83 1","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"2018-06-25","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"115538977","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2018-05-24DOI: 10.1093/ACREFORE/9780190647926.013.116
T. Dowling
Jet streams, “jets” for short, are remarkably coherent streams of air found in every major atmosphere. They have a profound effect on a planet’s global circulation and have been an enigma since the belts and zones of Jupiter were discovered in the 1600s. Collaborations between observers, experimentalists, computer modelers, and applied mathematicians seek to understand what processes affect jet size, strength, direction, shear stability, and predictability. Key challenges include nonlinearity, nonintuitive wave physics, nonconstant-coefficient differential equations, and the many nondimensional numbers that arise from the competing physical processes that affect jets, including gravity, pressure gradients, Coriolis accelerations, and turbulence. Fortunately, the solar system provides many examples of jets, and both laboratory and computer simulations allow for carefully controlled experiments. Jet research is multidisciplinary but is united by a common language, the conservation of potential vorticity (PV), which is an all-in-one conservation law that combines the conservation laws of mass, momentum, and thermal energy into a single expression. The leading theories of how jets emerge out of turbulence, and why they are invariably zonal (east-west orientated), reveal the importance of vorticity waves that owe their existence to conservation of PV. Jets are observed to naturally group into equatorial, midlatitude, and polar types. Earth and Uranus have weakly retrograde equatorial jets, but most planets exhibit strongly prograde (superrotating) equatorial jets, which require eddies to transport momentum up-gradient in a manner that is not obvious but is beginning to be understood. Jupiter and Saturn exhibit multiple alternating jets spanning their midlatitudes, with deep roots that connect to their interior circulations. Polar jets universally exhibit an impressive inhibition of meridional (north-south) mixing, and the seasonal nature of the polar jets on Earth, Mars, and Titan contrasts with the permanence of those on the giant planets, including Saturn’s beautiful north-polar hexagon. Intriguingly, jets in atmospheres have strong analogies with jets in nonneutral plasmas, with practical benefits to both disciplines.
{"title":"Jets in Planetary Atmospheres","authors":"T. Dowling","doi":"10.1093/ACREFORE/9780190647926.013.116","DOIUrl":"https://doi.org/10.1093/ACREFORE/9780190647926.013.116","url":null,"abstract":"Jet streams, “jets” for short, are remarkably coherent streams of air found in every major atmosphere. They have a profound effect on a planet’s global circulation and have been an enigma since the belts and zones of Jupiter were discovered in the 1600s. Collaborations between observers, experimentalists, computer modelers, and applied mathematicians seek to understand what processes affect jet size, strength, direction, shear stability, and predictability. Key challenges include nonlinearity, nonintuitive wave physics, nonconstant-coefficient differential equations, and the many nondimensional numbers that arise from the competing physical processes that affect jets, including gravity, pressure gradients, Coriolis accelerations, and turbulence. Fortunately, the solar system provides many examples of jets, and both laboratory and computer simulations allow for carefully controlled experiments. Jet research is multidisciplinary but is united by a common language, the conservation of potential vorticity (PV), which is an all-in-one conservation law that combines the conservation laws of mass, momentum, and thermal energy into a single expression. The leading theories of how jets emerge out of turbulence, and why they are invariably zonal (east-west orientated), reveal the importance of vorticity waves that owe their existence to conservation of PV.\u0000 Jets are observed to naturally group into equatorial, midlatitude, and polar types. Earth and Uranus have weakly retrograde equatorial jets, but most planets exhibit strongly prograde (superrotating) equatorial jets, which require eddies to transport momentum up-gradient in a manner that is not obvious but is beginning to be understood. Jupiter and Saturn exhibit multiple alternating jets spanning their midlatitudes, with deep roots that connect to their interior circulations. Polar jets universally exhibit an impressive inhibition of meridional (north-south) mixing, and the seasonal nature of the polar jets on Earth, Mars, and Titan contrasts with the permanence of those on the giant planets, including Saturn’s beautiful north-polar hexagon. Intriguingly, jets in atmospheres have strong analogies with jets in nonneutral plasmas, with practical benefits to both disciplines.","PeriodicalId":304611,"journal":{"name":"Oxford Research Encyclopedia of Planetary Science","volume":"49 1","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"2018-05-24","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"124746840","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2018-05-24DOI: 10.1093/ACREFORE/9780190647926.013.35
W. Grundy
Pluto orbits the Sun at a mean distance of 39.5 AU (astronomical units; 1 AU is the mean distance between the Earth and the Sun), with an orbital period of 248 Earth years. Its orbit is just eccentric enough to cross that of Neptune. They never collide thanks to a 2:3 mean-motion resonance: Pluto completes two orbits of the Sun for every three by Neptune. The Pluto system consists of Pluto and its large satellite Charon, plus four small satellites: Styx, Nix, Kerberos, and Hydra. Pluto and Charon are spherical bodies, with diameters of 2,377 and 1,212 km, respectively. They are tidally locked to one another such that each spins about its axis with the same 6.39-day period as their mutual orbit about their common barycenter. Pluto’s surface is dominated by frozen volatiles nitrogen, methane, and carbon monoxide. Their vapor pressure supports an atmosphere with multiple layers of photochemical hazes. Pluto’s equator is marked by a belt of dark red maculae, where the photochemical haze has accumulated over time. Some regions are ancient and cratered, while others are geologically active via processes including sublimation and condensation, glaciation, and eruption of material from the subsurface. The surfaces of the satellites are dominated by water ice. Charon has dark red polar stains produced from chemistry fed by Pluto’s escaping atmosphere. The existence of a planet beyond Neptune had been postulated by Percival Lowell and William Pickering in the early 20th century to account for supposed clustering in comet aphelia and perturbations of the orbit of Uranus. Both lines of evidence turned out to be spurious, but they motivated a series of searches that culminated in Clyde Tombaugh’s discovery of Pluto in 1930 at the observatory Lowell had founded in Arizona. Over subsequent decades, basic facts about Pluto were hard-won through application of technological advances in astronomical instrumentation. During the progression from photographic plates through photoelectric photometers to digital array detectors, space-based telescopes, and ultimately, direct exploration by robotic spacecraft, each revealed more about Pluto. A key breakthrough came in 1978 with the discovery of Charon by Christy and Harrington. Charon’s orbit revealed the mass of the system. Observations of stellar occultations constrained the sizes of Pluto and Charon and enabled the detection of Pluto’s atmosphere in 1988. Spectroscopic instruments revealed Pluto’s volatile ices. In a series of mutual events from 1985 through 1990, Pluto and Charon alternated in passing in front of the other as seen from Earth. Observations of these events provided additional constraints on their sizes and albedo patterns and revealed their distinct compositions. The Hubble Space Telescope’s vantage above Earth’s atmosphere enabled further mapping of Pluto’s albedo patterns and the discovery of the small satellites. NASA’s New Horizons spacecraft flew through the system in 2015. Its instruments mappe
{"title":"The Pluto−Charon System","authors":"W. Grundy","doi":"10.1093/ACREFORE/9780190647926.013.35","DOIUrl":"https://doi.org/10.1093/ACREFORE/9780190647926.013.35","url":null,"abstract":"Pluto orbits the Sun at a mean distance of 39.5 AU (astronomical units; 1 AU is the mean distance between the Earth and the Sun), with an orbital period of 248 Earth years. Its orbit is just eccentric enough to cross that of Neptune. They never collide thanks to a 2:3 mean-motion resonance: Pluto completes two orbits of the Sun for every three by Neptune. The Pluto system consists of Pluto and its large satellite Charon, plus four small satellites: Styx, Nix, Kerberos, and Hydra. Pluto and Charon are spherical bodies, with diameters of 2,377 and 1,212 km, respectively. They are tidally locked to one another such that each spins about its axis with the same 6.39-day period as their mutual orbit about their common barycenter. Pluto’s surface is dominated by frozen volatiles nitrogen, methane, and carbon monoxide. Their vapor pressure supports an atmosphere with multiple layers of photochemical hazes. Pluto’s equator is marked by a belt of dark red maculae, where the photochemical haze has accumulated over time. Some regions are ancient and cratered, while others are geologically active via processes including sublimation and condensation, glaciation, and eruption of material from the subsurface. The surfaces of the satellites are dominated by water ice. Charon has dark red polar stains produced from chemistry fed by Pluto’s escaping atmosphere.\u0000 The existence of a planet beyond Neptune had been postulated by Percival Lowell and William Pickering in the early 20th century to account for supposed clustering in comet aphelia and perturbations of the orbit of Uranus. Both lines of evidence turned out to be spurious, but they motivated a series of searches that culminated in Clyde Tombaugh’s discovery of Pluto in 1930 at the observatory Lowell had founded in Arizona. Over subsequent decades, basic facts about Pluto were hard-won through application of technological advances in astronomical instrumentation. During the progression from photographic plates through photoelectric photometers to digital array detectors, space-based telescopes, and ultimately, direct exploration by robotic spacecraft, each revealed more about Pluto. A key breakthrough came in 1978 with the discovery of Charon by Christy and Harrington. Charon’s orbit revealed the mass of the system. Observations of stellar occultations constrained the sizes of Pluto and Charon and enabled the detection of Pluto’s atmosphere in 1988. Spectroscopic instruments revealed Pluto’s volatile ices. In a series of mutual events from 1985 through 1990, Pluto and Charon alternated in passing in front of the other as seen from Earth. Observations of these events provided additional constraints on their sizes and albedo patterns and revealed their distinct compositions. The Hubble Space Telescope’s vantage above Earth’s atmosphere enabled further mapping of Pluto’s albedo patterns and the discovery of the small satellites. NASA’s New Horizons spacecraft flew through the system in 2015. Its instruments mappe","PeriodicalId":304611,"journal":{"name":"Oxford Research Encyclopedia of Planetary Science","volume":"42 1","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"2018-05-24","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"132446586","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
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