To understand the makeup of a distant atmosphere of a planet orbiting another star, astronomers capture the star's light that has filtered through it during a transit. It’s like guessing a soup recipe from the scent of steam as the pot briefly eclipses the bulb. The giant ELT telescope with its spectrograph ANDES will become a supersensitive nose, breaking down the aroma into thousands of hues. Computer simulations have shown: around red dwarfs, water vapor is the most noticeable “scent.” Water vapor on planet TRAPPIST-1 d would be detected in 10 observations, carbon dioxide in 15, methane in 30, and oxygen in 40. The irony: oxygen, the prime biosignature of life, is the hardest to sniff out. Out of 18 worlds, only 8 will yield a clear signal of any single gas within a reasonable timeframe. But TRAPPIST-1 d is a real concentrate: all four ingredients will reveal themselves in under 36 visits. However, even a giant like this will need years to catch a whiff of oxygen.