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Concept
Azote solide
Résumé
Solid nitrogen is a number of solid forms of the element nitrogen, first observed in 1884. Solid nitrogen is mainly the subject of academic research, but low-temperature, low-pressure solid nitrogen is a substantial component of bodies in the outer Solar System and high-temperature, high-pressure solid nitrogen is a powerful explosive, with higher energy density than any other non-nuclear material.
Karol Olszewski first observed solid nitrogen in 1884, by first liquefying hydrogen with evaporating liquid nitrogen, and then allowing the liquid hydrogen to freeze the nitrogen. By evaporating vapour from the solid nitrogen, Olszewski also generated the extremely low temperature of 48K, at the time a world record.
Modern techniques usually take a similar approach: solid nitrogen is normally made in a laboratory by evaporating liquid nitrogen in a vacuum. The solid produced is porous.
Solid nitrogen forms a large part of the surface of Pluto (where it mixes with solid carbon monoxide and methane) and the Neptunian moon Triton. On Pluto it was directly observed for the first time in July 2015 by the New Horizons space probe and on Triton it was directly observed by the Voyager 2 space probe in August 1989.Solid nitrogen has several properties relevant to its formation of rocks in the outer Solar System. Even at the low temperatures of solid nitrogen it is fairly volatile and can sublime to form an atmosphere, or condense back into nitrogen frost. Compared to other materials, solid nitrogen loses cohesion at low pressures and flows in the form of glaciers when amassed. Yet its density is higher than that of water ice, so the forces of buoyancy will naturally transport blocks of water ice towards the surface. Indeed, New Horizons observed "floating" water ice atop nitrogen ice on the surface of Pluto.
On Triton, solid nitrogen takes the form of frost crystals and a transparent sheet layer of annealed nitrogen ice, often referred to as a "glaze". Geysers of nitrogen gas were observed by Voyager 2 to spew from the subpolar regions around Triton's southern polar ice cap.
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