JWST has detected a new exoplanet that is six times the diameter of Jupiter.

In a study published on July 24 in *Nature*, an international team of 19 scientists reported the discovery of a new supergiant exoplanet orbiting the star Eps Ind A. The planet, named Eps Ind Ab, was observed using the James Webb Space Telescope (JWST) and has a mass at least six times that of Jupiter. With a temperature around -280 degrees Kelvin, Eps Ind Ab is the coldest exoplanet ever directly imaged.

Study co-author and postdoctoral researcher Elisabeth Matthews from the Max Planck Institute for Astronomy notes that cold supergiant planets like Eps Ind Ab are challenging to detect due to their faintness and the fact that much of their emitted light is in the mid-infrared spectrum. Observing mid-infrared light is difficult from Earth, making JWST’s capabilities in this range crucial for the discovery.

“Before JWST, we didn’t have a telescope capable of clearly separating the planet from its star and sensitive enough to capture mid-infrared wavelengths,” Matthews explains.

The presence of a giant planet around Eps Ind A was initially suggested in 2019, with further predictions about its characteristics detailed in studies from February and July 2023. However, JWST data revealed a planet with different properties than expected. Eps Ind A was found to be larger and farther from its star than previously thought. Additionally, the planet was unexpectedly bright in mid-infrared wavelengths, leading Matthews to express surprise that it had not been detected from Earth before.

The brightness of Eps Ind Ab in the mid-infrared is unusual because existing observations in the 4µm wavelength, where the system had been studied extensively, did not detect the planet. This suggests the possibility that the planet’s atmosphere might absorb light in this wavelength, potentially due to compounds like carbon monoxide, carbon dioxide, and methane. If this is correct, it would imply a higher abundance of these elements in the planet’s atmosphere, which could influence theories about its formation.

Matthews emphasizes that while this theory is intriguing, it requires further validation. The research team plans to use JWST’s spectroscopic instruments to analyze the planet’s atmosphere directly, which will provide more detailed information about its composition and formation.

Eps Ind Ab is a compelling subject for future research. Key questions remain about the planet’s atmosphere and its formation. However, it also offers a valuable opportunity for direct observations of a rare class of exoplanet, providing real-world data that can be used to test theoretical models.

Astronomers typically measure the brightness of stars, brown dwarfs, and planets to infer their masses. To accomplish this, scientists develop models that relate brightness to mass, simulating the formation and evolution of these celestial bodies. Eps Ind Ab presents a unique chance to test these models, particularly those related to thermal evolution at lower temperatures. The initial results are promising, indicating that the planet’s temperature aligns well with theoretical models of thermal evolution.

Looking ahead, Eps Ind Ab will continue to be a focus of research. The planet’s atmosphere composition and formation process are still not fully understood. Additionally, the fact that it allows for direct observation of a less common type of exoplanet makes it an excellent source for testing theoretical models.

Eps Ind Ab and its host star are part of a system that includes a “widely-separated brown dwarf binary.” According to Matthews, the brown dwarfs likely formed from the same material as Eps Ind Ab and its star, which could provide insights into the formation and evolution of these systems. Studying these interconnected systems could be highly valuable for refining models of their formation and evolution.

Future observations by the James Webb Space Telescope (JWST) are expected to offer further insights. Scheduled observations of the brown dwarfs will enable comparisons of their atmospheric chemistry with that of Eps Ind Ab, potentially enhancing our understanding of these celestial objects.