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Terrestrial helium consists almost exclusively (all but ~2ppm) [16] of 4 He. 4 He's boiling point of 4.2 K is the lowest of all known substances except 3 He. When cooled further to 2.17 K, it becomes a unique superfluid with zero viscosity. It solidifies only at pressures above 25 atmospheres, where it melts at 0.95 K.
The idea for the polar wind originated with the desire to solve the paradox of the terrestrial helium budget. This paradox consists of the fact that helium in the Earth's atmosphere seems to be produced (via radioactive decay of uranium and thorium) faster than it is lost by escaping from the upper atmosphere. The realization that some helium ...
Terrestrial planets are substantially different from the giant planets, which might not have solid surfaces and are composed mostly of some combination of hydrogen, helium, and water existing in various physical states. Terrestrial planets have a compact, rocky surfaces, and Venus, Earth, and Mars each also has an atmosphere. Their size, radius ...
Helium is inert - it does not react with other substances or combust - and its atomic number is 2, making it the second lightest element after hydrogen. Rockets need to achieve specific speeds and ...
The composition of a primary atmosphere is primarily hydrogen and helium, with minor amounts of other volatiles like water vapor, methane, and ammonia, depending on the temperature and region of the protoplanetary disk. These atmopsheres are generally thick and extended, enveloping the young planet in a dense layer of gas. [2]
Helium is a commonly used carrier gas for gas chromatography. The age of rocks and minerals that contain uranium and thorium can be estimated by measuring the level of helium with a process known as helium dating. [28] [30] Helium at low temperatures is used in cryogenics and in certain cryogenic applications.
Space physics, also known as space plasma physics, is the study of naturally occurring plasmas within Earth's upper atmosphere and the rest of the Solar System.It includes the topics of aeronomy, aurorae, planetary ionospheres and magnetospheres, radiation belts, and space weather (collectively known as solar-terrestrial physics [1]).
Helium planets would have a white or grey hue. (Artist's conception shown.) A helium planet is a planet with a helium-dominated atmosphere. This contrasts with ordinary gas giants such as Jupiter and Saturn, whose atmospheres consist primarily of hydrogen, with helium as a secondary component only. Helium planets might form in a variety of ways.