A quiet flute melody gets lost in the roar of drums. That's what astronomers face when trying to catch the faint light that has passed through a distant planet's atmosphere while its star blazes nearby.

A team of scientists observed WASP-31 b — a hot Jupiter, a gas giant orbiting very close to its star. They used the VLT in Chile and the ESPRESSO instrument, which splits light into colors like a prism. When the planet passes in front of its star, some starlight filters through its atmosphere, and gases leave their "fingerprints" in the spectrum — dark lines at specific wavelengths. But the star also has such lines, and they blend together, obscuring the planet's.

The scientists applied sophisticated methods to remove the interference, but even then they couldn't detect any gas in WASP-31 b's atmosphere. Earlier observations hinted at potassium and the molecule CrH, but those traces were not confirmed now. The reason isn't that the gases are absent, but that the contamination from the star is too strong.

It's like trying to make out a pattern on a glass pane with a bright lamp shining behind it. Until we figure out how to switch off the lamp or block it, the pattern stays invisible. Astronomers need new techniques to separate the planet's light from the star's, or even future giant telescopes won't help.