As the comparatively large planet – in a size-class known as “super Neptune” – crosses the face of its smallish star, starlight shining through its atmosphere can be more easily analyzed by our telescopes.
Those equipped with special instruments called spectrographs – including the just-launched James Webb Space Telescope – can spread this light into a spectrum, revealing which gases are present in the planet’s atmosphere.
If the Webb telescope, once it’s up and running, is turned on TOI-674 b, it should be able to examine the planet’s atmosphere in far more detail.