Molten glass rain and planet‑wide lava oceans now sit in telescope data, not in a movie script. The route to these worlds runs through unforgiving measurements: tiny dips in starlight, minute stellar wobbles, and faint heat signatures sliced into spectra.
Transit photometry tracks how a star’s brightness falls when a planet crosses its face. From the depth and shape of that light curve, astronomers extract radius, orbital period, and often dayside temperature. In extreme cases, the irradiated hemisphere reaches well beyond two thousand degrees Celsius, hot enough to keep silicate rock in a molten state and sustain an incandescent magma ocean across a hemisphere.
Radial‑velocity data add mass by measuring Doppler shifts in the star’s spectrum, turning light into a gravitational balance sheet. Once mass and radius are known, bulk density distinguishes gas giants from super‑dense rocky worlds that can host surface lava. During transit, transmission spectroscopy isolates starlight that has filtered through a planet’s limb, revealing absorption lines from molecules such as sodium, titanium oxide, or vaporized silicates that imply glass‑forming material suspended in the atmosphere.
Thermal emission spectra, captured when a planet slips behind its star, measure the dayside’s blackbody‑like glow directly. Phase curves then trace brightness changes over an orbit, mapping how heat is advected by atmospheric circulation rather than merely assumed from equilibrium temperature. The result is a class of measured environments where clouds can condense from rock, winds can drive horizontal temperature gradients of hundreds of degrees, and nightsides can host solidifying lava that returns to vapor when dawn arrives.
