Hydrogen is the ninth most abundant chemical element on Earth. The entire universe consists of more than 90% hydrogen, in the stars in a plasma state and interstellar matter mostly in an atomic state. In the solar system, aside from the sun, interplanetary gas as well as the outer planets (Jupiter, Saturn, Uranus and Neptune) consist primarily of hydrogen.
KeywordsEnergy Carrier Liquid Hydrogen Outer Planet Interstellar Matter Rocket Propulsion
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