Kevin B. Stevenson

The three planets in the Kepler-51 system have long intrigued astronomers: they are Saturn-sized but less dense than water. These 'super-puff' worlds, with masses no more than ten Earths, are like cosmic dandelions — massive yet almost weightless. Their orbits are arranged like musicians in an orchestra, each playing its part, beating the rhythm with transits.

In 2023, the James Webb Space Telescope turned its gaze toward a distant star in the constellation Virgo. Orbiting it is HAT-P-26 b, a warm Neptune, a world with a mass of 18.6 Earths and a radius of 6.33 Earths. The planet transited across the star's disk, and at that moment its atmosphere became briefly visible.

Astronomers couldn't understand why the 'hot Neptune desert' — a region right next to stars — has almost no Neptune-sized planets. It was thought that there they are doomed: the star's proximity boils off the atmosphere, leaving a bare rocky core. But the exoplanet LTT-9779 b, 29 times heavier than Earth and with a 19-hour orbit, survived.

Eavesdropping on a distant planet's atmosphere is hampered by the star's noise. In the TRAPPIST-1 system, astronomers used a planet-"bug": TRAPPIST-1 b — an airless neighbor that records only the interference.

Some 158 light-years away, around the dim star TOI-6894, a red dwarf, a planet moves leisurely. Its year lasts less than two Earth days, yet it is a cool world with an equilibrium temperature around 420 K, just a bit warmer than a sauna.

Hundreds of light-years away, there's a planet that looks like a giant mirror. LTT9779b reflects most of the light that hits it — far more than you'd expect from a Neptune-sized body. Astronomers have long debated what makes it so shiny: a thick carbon-rich haze or a layer of clouds. The James Webb Space Telescope has helped settle the debate.