Astronomy has taken a further step in the study of distant worlds thanks to an unprecedented capture: the james webb space telescope has managed to directly photograph a cold exoplanet located just 12 light years of the Earth. It is about Epsilon Indi Ab, a gas giant planet that, due to its characteristics, allows us to look into the evolutionary history of our own solar system with a precision never before achieved.
On this occasion, researchers have used the instrument's advanced coronagraph MIRI (Mid-Infrared) to separate the planet’s light from the blinding luminosity of its host star, Epsilon Indi A. The result is the sharpest and most detailed image of such a cool exoplanet ever obtained, a milestone only possible with Webb’s pioneering technology.
The discovery of Epsilon Indi Ab It is not only relevant because of its proximity to Earth, but also because of its rarity: planets of this type, with such low temperatures and that have been able to be directly observed, barely number a few dozen in the current record.
An unusual portrait: Epsilon Indi Ab, the most studied cold exoplanet
The planet Epsilon Indi Ab It has intrigued the scientific community for years. Its existence was known thanks to indirect measurements, especially through the radial velocity technique, which detects the tiny wobbles of a star caused by the gravity of a massive planet. However, until now, no one had been able to observe it directly.
Using the sensitivity of MIRIThe James Webb telescope captured the infrared light emitted by Epsilon Indi Ab itself. This strategy is crucial for detecting cool planets, whose residual heat is no longer sufficient to emit in the visible, but which can still be revealed in the mid-infrared. The image shows a point-like body, unresolved in a disk, where the 10,6-micron light appears in blue tones and the 15,5-micron light appears in orange. The location of the primary star is marked, although its light has been eliminated by the coronagraph.
The result is doubly valuable: not only confirms the existence of the planet and its fundamental properties, but also allows its atmospheric characteristics to be compared with those of the gas giants in our solar system.
With an estimated temperature of only 2 degrees Celsius Epsilon Indi Ab—practically on par with liquid water on Earth—is one of the coldest exoplanets with the most direct and detailed observations. This makes it an essential reference for studying atmospheres rich in compounds such as methane, carbon monoxide, and carbon dioxide, which could be present in large quantities and substantially modify the absorption profile of the light reaching us.
A natural laboratory for understanding the evolution of planetary systems
The star Epsilon Indi A, host of this exoplanet, is an orange dwarf somewhat cooler and of a similar age to our Sun. That such a massive and cold planet orbits a star of this type offers astronomers the possibility of Investigate processes of planetary formation and atmospheric evolution in contexts very similar to and yet far from our own..
According to the researcher Caroline Morley (University of Texas at Austin), until now the presence of Epsilon Indi Ab had only been deduced through indirect analysis. Choosing it as a priority target for the James Webb was in response to the expectation of finding a planet “more similar to Jupiter than any other photographed so far.”
The lead author, Elisabeth Matthews (Max Planck Institute for Astronomy, Germany), points out that most of the exoplanets observed directly to date were young, hot bodies. “As they cool and contract over their lifetime, planets become much less luminous and more difficult to study,” Matthews explains. This is one of the main challenges for the mature exoplanet astrophysics.
Epsilon Indi Ab is therefore a rare opportunity to examine a gas giant at an advanced evolutionary stage, similar to that of larger bodies in our own solar system.
The most interesting thing for experts is the possibility of analyze atmospheric composition accurately. Epsilon Indi Ab is only about 100 degrees warmer than Jupiter and Saturn, allowing for a comparison of large-scale cooling, contraction, and atmospheric clearance processes. Moreover, compared to free-floating brown dwarfs, Epsilon Indi Ab is even cooler, allowing for a study of how closely current models reflect observed reality.
It surprises even the scientists themselves
Although the presence of Epsilon Indi Ab had been predicted by the radial velocity patterns of its star, its real parameters baffled the teamThe planet turned out—according to Webb observations—to have almost twice the expected mass, orbit somewhat farther from its star, and follow a different orbit than initially predicted. This discrepancy between theoretical predictions and direct measurements highlights the complexity of planetary systems and the need to study more field cases with real data.
The team also points to some atmospheric peculiarity that makes the data difficult to interpret. According to initial analyses, Epsilon Indi Ab is less bright than expected at shorter wavelengths, which could be due to a atmosphere heavily laden with methane and other absorbing gases or a dense cloud coverThis behavior, unusual for planets with similar characteristics, opens up new lines of research into the chemical and physical processes that control planetary atmospheres under extreme temperature conditions.
At the moment, the group has limited photometric measurements, and further spectroscopic observations will be needed to determine exactly which components dominate the atmosphere and how they affect the radiation flux.
