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Article

Frans von der Dunk

International satellite law can best be described as that subset of international space law that addresses the operations of satellites in orbit around the Earth. Excluding, therefore, topics such as manned space flight, suborbital space operations, and any activities beyond Earth orbits, this means addressing the use of satellites for telecommunications purposes, for Earth observation and remote sensing, and for positioning, timing, and navigation. These three major sectors of space activities are, in addition to jointly being subject to the body of international space law, each subject to their specific dedicated legal regime—international satellite communications law, international satellite remote sensing law, and international satellite navigation law.

Article

Probing the interiors of the gaseous giant planets in our solar system is not an easy task. It requires a set of accurate measurements combined with theoretical models that are used to infer the planetary composition and its depth dependence. The masses of Jupiter and Saturn are 317.83 and 95.16 Earth masses (M ⊕ ), respectively, and since a few decades, it has been known that they mostly consist of hydrogen and helium. The mass of heavy elements (all elements heavier than helium) is not well determined, nor are their distribution within the planets. While the heavy elements are not the dominating materials inside Jupiter and Saturn, they are the key to understanding the planets’ formation and evolutionary histories. The planetary internal structure is inferred from theoretical models that fit the available observational constraints by using theoretical equations of states (EOSs) for hydrogen, helium, their mixtures, and heavier elements (typically rocks and/or ices). However, there is no unique solution for determining the planetary structure and the results depend on the used EOSs as well as the model assumptions imposed by the modeler. Major model assumptions that can affect the derived internal structure include the number of layers, the heat transport mechanism within the planet (and its entropy), the nature of the core (compact vs. diluted), and the location (pressure) of separation between the two envelopes. Alternative structure models assume a less distinct division between the layers and /or a non-homogenous distribution of the heavy elements. The fact that the behavior of hydrogen at high pressures and temperatures is not perfectly known and that helium may separate from hydrogen at the deep interior add sources of uncertainty to structure models. In the 21st century, with accurate measurements of the gravitational fields of Jupiter and Saturn from the Juno and Cassini missions, structure models can be further constrained. At the same time, these measurements introduce new challenges for planetary modelers.

Article

Elina Morozova and Yaroslav Vasyanin

International space law is a branch of international law that regulates the conduct of space activities. Its core instruments include five space-specific international treaties, which were adopted under the auspices of the United Nations. The first and the underlying one—the Treaty on Principles Governing the Activities of States in the Exploration and Use of Outer Space, including the Moon and Other Celestial Bodies (Outer Space Treaty)—establishes that outer space is free for exploration and use by all states. Such fundamental freedom is exercised by a number of space applications that have become an integral part of modern human life and global economy. Among such applications, satellite telecommunications is the most widespread, essential, and advanced. Indeed, since 1957 when the Soviet Union launched Sputnik 1, the first artificial satellite merely capable of continuous beeping during its 21-day trip around the globe, space technologies have progressed in leaps and bounds. Cutting-edge satellite telecommunications methods ensure instant delivery of huge amounts of data, relay of real-time voice and video, broadcasting of radio and television, and Internet access worldwide. By transmitting signals over any distance telecommunications satellites connect locations everywhere on Earth. A telecommunications satellite’s lifetime, starting from the launch and ending at de-orbiting, is governed by international space law. The latter considers satellites as “space objects” and regulates liability, registration, jurisdiction and control, debris mitigation, and touches upon ownership. Therefore, the first large group of international law rules applicable to satellite telecommunications includes provisions of three out of five UN space treaties, specifically, the 1967 Outer Space Treaty, the 1972 Convention on International Liability for Damage Caused by Space Objects, and the 1976 Convention on Registration of Objects Launched into Outer Space, as well as several UN General Assembly resolutions. To carry out a communication function, satellites need to be placed in a certain orbit and to use radio-frequency spectrum, both limited natural resources. Access to these highly demanded resources, which are not subject to national appropriation and require rational, efficient, and economical uses in an interference-free environment, is managed by the International Telecommunication Union (ITU)—the UN specialized agency for information and communication technologies. The ITU’s core regulatory documents are its Constitution, Convention, and the Radio Regulations, which collectively make up another group of international law rules relevant to satellite telecommunications. Both groups of international law rules constitute the international legal regime of satellite telecommunications and face the challenge of keeping pace with technology advancement and market evolution, as well as with a growing number of states and non-state actors carrying on space activities. These tangible changes need to be addressed in the regulatory framework that cannot but serve as a driver for further development of satellite telecommunications.

Article

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.

Article

Throughout the history of human activity in outer space, the role of private companies has steadily grown, and, in some cases, companies have even replaced government agencies as the primary actors in space. As private space activity has grown and diversified, the laws and regulations that govern private actors have been forced to evolve in reaction to the new realities of the industry. On the international level, the treaties concluded in the 1960s and 1970s continue to be in force today. However, these treaties only govern state activity in space. The rules regulating private industry are necessarily domestic in nature, and it is in these domestic laws that the evolution of space law can be most clearly seen. That said, new industries, such as asteroid mining, are testing the limits of international law and have forced the international community to examine whether changes to long-standing laws are needed.

Article

Pascal Rosenblatt, Ryuki Hyodo, Francesco Pignatale, Antony Trinh, Sebastien Charnoz, Kevin Dunseath, Mariko Dunseath-Terao, and Hidenori Genda

The origin of the natural satellites or moons of the solar system is as challenging to unravel as the formation of the planets. Before the start of the space probe exploration era, this topic of planetary science was restricted to telescopic observations, which limited the possibility of testing different formation scenarios. This era has considerably boosted this topic of research, particularly after the Apollo missions returned samples from the Moon’s surface to Earth. Observations from subsequent deep space missions such as Viking 1 and 2 Orbiters, Voyager 1 and 2, Phobos-2, Galileo, Cassini-Huygens, and the most recent Mars orbiters such as Mars Express, as well as from the Hubble space telescope, have served to intensify research in this area. Each moon system has its own specificities, with different origins and histories. It is widely accepted that the Earth’s Moon formed after a giant collision between the proto-Earth and a body similar in size to Mars. The Galilean moons of Jupiter, on the other hand, appear to have formed by accretion in a circum-Jovian disk, while smaller, irregularly shaped satellites were probably captured by the giant planet. The small and medium-sized Saturnian moons may have formed from the rings encircling the planet. Among the terrestrial planets, Mercury and Venus have no moons, the Earth has a single large moon, and Mars has two very small satellites. This raises some challenging questions: What processes can lead to moon formation around terrestrial planets and what parameters determine the possible outcomes, such as the number and size of moons? The answer to such fundamental questions necessarily entails a thorough understanding of the formation of the Martian system and may have relevance to the possible existence of (exo)moons orbiting exoplanets. The formation of such exomoons is of great importance as they could influence conditions for habitability or for maintaining life over long periods of time on the surface of Earth-like exoplanets, for example by limiting the variations of the orientation of the planet’s rotation axis and thus preventing frequent changes of its climate. Our current knowledge concerning the origin of Phobos and Deimos has been acquired from observational data as well as theoretical work. Early observations led to the idea that the two satellites were captured asteroids but this created difficulties in reconciling the current orbits of Phobos and Deimos with those of captured bodies, hence suggesting the need for an alternative theory. A giant-impact scenario provides a description of how moons similar to Phobos and Deimos can be formed in orbits similar to those observed today. This scenario also restricts the range of possible composition of the two moons, providing a motivation for future missions that aim for the first time to bring material from the Martian system back to Earth.

Article

Shortly after the launch of the first manmade satellite in 1957, the United Nations (UN) took the lead in formulating international rules governing space activities. The five international conventions (the 1967 Outer Space Treaty, the 1968 Rescue Agreement, the 1972 Liability Convention, the 1975 Registration Convention, and the 1979 Moon Agreement) within the UN framework constitute the nucleus of space law, which laid a solid legal foundation securing the smooth development of space activities in the next few decades. Outer space was soon found to be a place with abundant opportunities for commercialization. Telecommunications services proved to be the first successful space commercial application, to be followed by remote sensing and global navigation services. In the last decade, the rapid development of space technologies has brought space tourism and space mining to the forefront of space commercialization. With more and more commercial activities taking place on a daily basis from the 1980s, the existing space law faces severe challenges. The five conventions, enacted in a time when space was monopolized by two superpowers, failed to take into account the commercial aspect of space activities. While there is an urgent need for new rules to deal with the ongoing trend of space commercialization, international society faces difficulties in adopting new rules due to diversified concerns over national interests and adjusts the legislative strategies by enacting soft laws. In view of the difficulty in adopting legally binding rules at the international level, states are encouraged to enact their own national space legislation providing sufficient guidance for their domestic space commercial activities. In the foreseeable future, it is expected that the development of soft laws and national space legislation will be the mainstream regulatory activities in the space field, especially for commercial space activities.