- 2
- Atomic numberThe second-lightest element. Only hydrogen is lighter.
- −269 °C
- Boiling pointThe coldest liquid known, which is why it cools MRI magnets and quantum computers.
- Inert
- Safe and stableIt does not burn and does not react with other substances.
- Escapes
- Rare on EarthCommon in the universe, but so light that once released it rises and is lost to space.
Found in the Sun first. In 1868, astronomers saw an unknown yellow line in sunlight and named the element after helios, the Greek word for Sun. It was first found on Earth in 1895, inside a uranium-bearing mineral. Sun image: NASA/SDO, public domain.