The helium in a party balloon is the very gas that makes it float. But long before balloons, helium appeared in the first minutes after the Big Bang. Its exact abundance in the universe is like a fingerprint: it tells you how many kinds of neutrinos (ghostly particles that pass through walls) exist.
Astronomers have found a way to measure this fingerprint more accurately. They look at distant clouds of hot hydrogen that contain almost no heavy elements, such clouds preserve the composition of the early universe. A new method for analyzing spectra obtained with the Large Binocular Telescope in Arizona allows them to determine the helium fraction with an uncertainty of about 2% for each cloud. And by selecting the best clouds, the scientists hope to achieve an overall precision of 0.5%.
Why such precision? The number of neutrino types in the Standard Model of particle physics is three. But if helium measurements point to a different value, that would hint at new physics — for instance, the existence of sterile neutrinos that do not interact with matter. So a precise helium count in ancient gas is a test of the very foundations of our understanding of the world.
Helium was first found on the Sun, not on Earth: in 1868, astronomers spotted an unknown line in the solar spectrum and named the element after Helios, the Greek god of the Sun.
In Stanislaw Lem's novel Solaris, the planet's ocean is made of an unknown form of matter; precise measurements of cosmic composition could help distinguish ordinary matter from exotic matter.