A bare rock under a blazing sun: that’s exoplanet GJ 3929 b. Its year lasts just 2.6 days, and it always shows the same face to its star. Discovered via the transit method (catching a shadow against the star), perfected by William Borucki, this planet heats up to 370°C on the dayside — enough to melt lead. The nearby dwarf star bombards it with a hurricane of radiation, stripping the atmosphere like a cosmic sandblaster.

To see if any gas blanket survived, scientists pointed the JWST telescope and caught the planet’s heat just as it slipped behind the star. Photometry (precise light counting) showed: no thick shell of carbon dioxide, like on Venus, exists. Light hydrogen escaped long ago, but a thin, almost ghostly atmosphere could have eluded the detectors.

Without a thick blanket, though, the night side is likely plunged into icy darkness. This world is split in two: eternal fire and eternal cold. To see if anything else is there, we’ll need spectroscopy — splitting light into colors to reveal the chemical makeup.