What secrets lurk inside distant planets? Sulfur holds the clue. ✛ ✎

A planet’s atmosphere is like steam above a pot: its composition depends on what’s “cooking” inside. But the light of its host star, like a flame, changes that steam. In a new study, scientists figured out how these changes reveal the inner workings of exoplanets — worlds around other stars. The key turned out to be sulfur, which leaves noticeable traces in the atmosphere.

The main tool is the transit method: when an exoplanet blocks part of its host star’s disk, light rays pierce its atmosphere and leave characteristic molecular “fingerprints” in the spectrum. This spectroscopy technique (splitting light into colors) was advanced by David Charbonneau, among others. Meanwhile, computer simulations helped predict how different gas mixtures behave under radiation from stars like the Sun and red dwarfs — small but active stars.

It turned out that the spectral clues from sulfur are directly tied to the mantle’s redox state — roughly speaking, how much oxygen lurks in the depths. This discovery gives astronomers a reliable marker for finding planets similar to ours.