“When we determine the abundance of a certain element in a star or a galaxy or a gas cloud anywhere in the universe, we use the sun as a reference point.” “The sun is a fundamental yardstick,” says Martin Asplund, an astrophysicist at the Max Planck Institute for Astrophysics in Garching, Germany.

Robberto (Space Telescope Science Institute/ESA) and the Hubble Space Telescope Orion Treasury Project Team Although the sun’s exact oxygen abundance is controversial, no one disputes that stars much more massive than the sun - similar to the brightest stars now being born in the Orion Nebula (shown) - forged most of the oxygen found today on Earth and throughout the universe. As a result, they don’t know what the other stars are made of, either. Astonishingly, scientists don’t know exactly what the sun is made of. The problem lies not in the far corners of the cosmos, but much closer to home.

Twenty years ago, astronomers expressed confidence in the numbers they had been working with. These numbers are crucial, because they affect how stars live and die, what types of planets form and even how readily life might arise on other worlds. Surprisingly, no one knows the stars’ exact chemical composition: how many carbon, nitrogen and oxygen atoms they have relative to hydrogen, the most common element. It’s not just the true nature of dark matter that eludes them so does the essence of the stars that speckle the sky and populate the many galaxies throughout the cosmos. As astronomers gaze into the depths of space, they do so with unease: They don’t know precisely what the universe is made of.

Issue with sodium element