Mercury is a small, rocky planet about which researchers know relatively little. Two missions, taking readings as they passed over the planet, have revealed that Mercury is covered by an iron-poor and sulfur-rich crust. It is also reduced, a chemical state in which the substances have gained electrons. In fact, it’s the most reduced planet in the solar system.

The Perseus Cluster is a massive galaxy cluster located in the constellation Perseus. It is one of the largest structures in the observable universe, comprising more than a thousand galaxies—equivalent to roughly a thousand trillion times the mass of the sun. Hot gases within the cluster, known as the intracluster medium (ICM), emit powerful X-rays detectable by telescopes. These gases are produced by billions of supernova explosions, and their chemical composition reveals how typical supernovae have exploded throughout cosmic history.