Oxford Research Encyclopedia of Planetary Science最新文献

{"title":"Water Ice at Mid-Latitudes on Mars","authors":"F. Butcher","doi":"10.1093/acrefore/9780190647926.013.239","DOIUrl":"https://doi.org/10.1093/acrefore/9780190647926.013.239","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 Mars’ mid-latitudes (roughly 30–60° N and S) host voluminous deposits of water ice in the subsurface. At present, perennial water ice cannot exist at the surface in these regions. This is because, for a significant portion of the Martian year, surface temperatures exceed the sublimation point of water ice under Mars’ low atmospheric pressure. Therefore, any seasonal water-ice frost that accumulates in winter sublimates back into the atmosphere in spring. However, a centimeters-to-meters-thick covering of lithic material can inhibit sublimation sufficiently to allow perennial stability of ice in the subsurface. Perennial ice in Mars’ mid-latitudes exists as pore-ice and excess-ice lenses within the regolith, and as massive accumulations of buried, high-purity ice akin to debris-covered glaciers on Earth. The ice is thought to range in age from hundreds of thousands to many hundreds of millions of years old. Its emplacement and modification has been widely attributed to cyclical climate changes induced by variations in Mars’ orbital parameters (primarily its axial tilt). Water ice in Mars’ mid-latitudes is therefore of significant interest for reconstructing such climate changes. It could also provide an essential in situ supply of water for future human missions to Mars. It is possible to infer the presence of water ice in Mars’ subsurface without direct imaging of the ice itself. For example, the distribution of near-surface ice was mapped using Mars Odyssey Neutron Spectrometer detections to calculate the percentage of water-equivalent hydrogen in the upper 1 m of the regolith. Orbital images have revealed a great diversity of ice-related landforms which suggest flow, thermal cycling, sublimation, and disruption (e.g. by impact cratering) of subsurface ice. In some locations, orbital ground-penetrating radar observations have been used to confirm subsurface ice content in areas where its presence has been inferred from the geomorphology of the surface. Water ice in Mars’ mid-latitudes has also been imaged directly by landed and orbital missions. The Phoenix lander exposed water-ice lenses just centimeters beneath the surface, in trenches that it excavated at 68 °N latitude. Orbital images from the High Resolution Imaging Science Experiment (HiRISE) camera on board Mars Reconnaissance Orbiter revealed transient bright ice deposits exhumed by small, fresh impacts into mid-latitude terrains, and ~100 m-high scarps of water ice in exposures through debris-covered ice deposits. In all these cases, the exposed ice has been observed to lose mass by sublimation over time. This demonstrates the essential role of lithic cover in preserving subsurface water ice in Mars’ mid-latitudes.","PeriodicalId":304611,"journal":{"name":"Oxford Research Encyclopedia of Planetary Science","volume":"07 1","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"1900-01-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"130176161","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}

{"title":"Telecommunication Law","authors":"M. Hofmann","doi":"10.1093/acrefore/9780190647926.013.85","DOIUrl":"https://doi.org/10.1093/acrefore/9780190647926.013.85","url":null,"abstract":"Telecommunication law is a broad complex of legal rules, the aim of which is to regulate telecommunication services—the conveyance of signals by means of telecommunication networks; it also covers satellite and space research services. The utmost purpose of these norms is to enable an interference-free transmission of signals, both on a domestic and an international scale. Telecommunication law is composed of three levels of regulations: international, regional, and domestic. The international regulation is performed traditionally by states organized in the International Telecommunication Union on the basis of the ITU Constitution, Convention, and Radio Regulations; trade aspects of telecommunications are regulated by the World Trade Organization. There are several regional cooperation structures dealing with telecommunications; the telecommunication framework of the European Union can serve as an example of a highly harmonized regional regulation based on the Electronic Communication Code. Domestic telecommunication laws are adopted by sovereign states; however, the international rules and regional regulations influence their content and structure. These legal mechanisms are very useful regulatory frameworks that guarantee that telecommunication signals are conveyed to their consumers without administrative and factual obstacles. They have functioned for decades on a pragmatic basis driven mostly by technical and economic needs.","PeriodicalId":304611,"journal":{"name":"Oxford Research Encyclopedia of Planetary Science","volume":"27 1","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"1900-01-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"128970945","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}

{"title":"Astrobiology (Overview)","authors":"S. McMahon","doi":"10.1093/acrefore/9780190647926.013.1","DOIUrl":"https://doi.org/10.1093/acrefore/9780190647926.013.1","url":null,"abstract":"Astrobiology seeks to understand the origin, evolution, distribution, and future of life in the universe and thus to integrate biology with planetary science, astronomy, cosmology, and the other physical sciences. The discipline emerged in the late 20th century, partly in response to the development of space exploration programs in the United States, Russia, and elsewhere. Many astrobiologists are now involved in the search for life on Mars, Europa, Enceladus, and beyond. However, research in astrobiology does not presume the existence of extraterrestrial life, for which there is no compelling evidence; indeed, it includes the study of life on Earth in its astronomical and cosmic context. Moreover, the absence of observed life from all other planetary bodies requires a scientific explanation, and suggests several hypotheses amenable to further observational, theoretical, and experimental investigation under the aegis of astrobiology. Despite the apparent uniqueness of Earth’s biosphere— the “n = 1 problem”—astrobiology is increasingly driven by large quantities of data. Such data have been provided by the robotic exploration of the Solar System, the first observations of extrasolar planets, laboratory experiments into prebiotic chemistry, spectroscopic measurements of organic molecules in extraterrestrial environments, analytical advances in the biogeochemistry and paleobiology of very ancient rocks, surveys of Earth’s microbial diversity and ecology, and experiments to delimit the capacity of organisms to survive and thrive in extreme conditions.","PeriodicalId":304611,"journal":{"name":"Oxford Research Encyclopedia of Planetary Science","volume":"1 1","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"1900-01-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"130928996","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}