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Three and a half parsecs from the Sun, among the dim stars of the southern sky, hides a world that astronomers have been trying to see for thirty years. Epsilon Indi Ab is a gas giant, cold as a winter night: its temperature is about 275 kelvins, just above the freezing point of water. It lies so far from its star that a year there lasts longer than a human lifetime, and the star's light barely warms its upper layers.

Now this world is no longer just a dot on a graph. The James Webb Space Telescope turned its infrared eyes on the planet and captured images in the range from 4 to 25 micrometers, as if we had finally seen the face of a person we previously knew only by footsteps in the dark. The longest-wavelength frame, at 25 micrometers, set a record: no exoplanet had ever been photographed in such "thermal" light.

The new images allowed scientists to assemble the first-ever spectrum of thermal emission from a cold gas giant outside the Solar System — from 4 to 25 micrometers. A spectrum is light split into its colors, and it reveals the composition of the atmosphere. It turns out that Epsilon Indi Ab's air is rich in heavy elements — astronomers call this "metallicity," though it has little to do with metals in the everyday sense. Such enrichment was predicted by models: the more massive a planet, the more rocky material it gathered at birth.

There is also a hint of clouds. Water vapor in the planet's atmosphere should absorb some infrared light, making the planet appear dimmer at certain wavelengths. But the measurements showed that at 25 micrometers the planet is brighter than expected. The simplest explanation is that clouds of water-ice crystals hang in the upper atmosphere, reflecting heat back into space like a snowfield reflecting sunlight.

The system's age is estimated at 3.5 billion years — the planet has long cooled and no longer contracts like young hot giants. Comparing the measured luminosity with predictions from evolutionary models, astronomers found excellent agreement. This means our ideas about how gas giants age work even at the edge of what we've studied — with faint glow, low mass, and respectable age.

Epsilon Indi Ab is becoming a benchmark: now, when looking at other cold worlds, scientists will check them against this neighbor. And its atmosphere is the first of its kind to be split into colors so far into the infrared. Thirty years of observations have turned a dot into a world with weather, chemistry, and history.