Two nearby exoplanets have yielded their clearest climate portrait yet
Astronomers have produced the first temperature maps of two Earth-sized exoplanets orbiting another star, using the James Webb Space Telescope to study TRAPPIST-1b and TRAPPIST-1c across complete orbits. The result is a stark one: both worlds appear to be rocky, airless planets with brutally uneven climates, their star-facing hemispheres heated to extremes while their permanent night sides plunge far below freezing.
The observations focus on the two innermost planets in the TRAPPIST-1 system, a compact seven-planet family circling a red dwarf star about 40 light-years from Earth. The system has been a major target for exoplanet science ever since its discovery, partly because several of its worlds lie in or near the star’s habitable zone and partly because red dwarfs are the most common stars in the Milky Way. Understanding what kinds of atmospheres their planets can retain is therefore central to the broader search for potentially habitable environments beyond the Solar System.
In the new work, an international team from the Universities of Geneva and Bern used Webb to observe TRAPPIST-1b and 1c continuously in infrared light for a total of 60 hours. By measuring thermal emission from each planet as it moved around its star, the researchers reconstructed how much heat was being radiated from the day side and the night side. That allowed them to create detailed temperature maps rather than infer climate conditions from more limited snapshots.
Tidally locked worlds with no sign of atmospheric heat transfer
The defining condition on both planets is tidal locking. Like the Moon’s relationship with Earth, the planets rotate in sync with their orbits, meaning the same face always points toward their star. On such worlds, there is no ordinary day-night cycle. One hemisphere experiences perpetual daylight, while the other remains in permanent darkness. If a substantial atmosphere exists, it can transport heat between the two sides and soften the temperature contrast. If no atmosphere is present, the thermal divide should be extreme.
That is essentially what Webb saw. TRAPPIST-1b reaches temperatures above 200 degrees Celsius on its day side, while the night side falls below minus 200 degrees Celsius. TRAPPIST-1c showed a similar pattern. Those huge contrasts are the key scientific result because they imply that heat is not being redistributed efficiently around either planet. In other words, there is no evidence in these observations for an atmosphere thick enough to smooth conditions between the hemispheres.
This finding narrows the range of possible interpretations for the two planets. The simplest reading is that both are bare rocky worlds. They are close to their parent star, heavily irradiated, and unable to maintain the kind of atmosphere that could moderate climate or support surface conditions remotely similar to Earth’s. That does not make the system less interesting. It makes it more legible. Exoplanet science often advances by ruling out plausible worlds as much as by identifying promising ones.
