Jupiter is a case study in solar system superlatives. The gas giant is the biggest planet orbiting the sun, it’s the most massive, and new evidence suggests it’s also the oldest (Proc. Natl. Acad. Sci. USA 2017, DOI: 10.1073/pnas.1704461114). Using mass spectroscopy, researchers from Lawrence Livermore National Laboratory and the University of Münster observed that Earth’s iron meteorite samples cluster into two groups: those that are enriched in heavier isotopes of tungsten and molybdenum and those that aren’t. These data suggest that the solar system once had two distinct reservoirs where meteoric material amassed. Something must have kept these reservoirs separate, and a baby Jupiter, roughly 20 times the mass of Earth, is the likeliest explanation, say researchers led by Livermore’s Thomas S. Kruijer. On the basis of the ages of the dichotomous samples, the team posits that Jupiter’s birthday was about 1 million years after the formation of the solar system. That’s within the predicted age range of Jupiter, but at its oldest end. Jupiter continued growing after its formation and eventually became massive enough to help stir up the reservoirs. Today, billions of years later, meteorites still carry clues that chemists can study to learn about the early solar system.