An exoplanet known as Kepler-51d has an extremely thick haze layer, which has become the main obstacle in recent observations made by Telescópio Espacial James Webb. Localizado approximately 2,615 light years from Terra, in the constellation of Cisne, the planet orbits a star similar to Sol with an estimated age of 500 million years. The haze blocked the atmosphere’s chemical signatures, preventing scientists from identifying specific elements and better understanding their unusual formation.
Universidade Estadual researchers from Pensilvânia led the study, which analyzed starlight as it passed through the planet’s atmosphere during a transit. The data showed a tilted transmission spectrum with almost no distinct features at wavelengths from 0.6 to 5.3 microns, captured by the NIRSpec-PRISM instrument. Essa slope indicates the presence of aerosol particles at high altitudes, which scatter and absorb light efficiently.
Kepler-51d is part of a rare star system with planets classified as “super-puffs” or super-bloated. Esses worlds exhibit sizes comparable to those of gas giants like Saturno, but very low masses, resulting in extremely reduced densities. In the case of Kepler-51d, the density reaches around 0.038 g/cm³, similar to that of cotton candy, with a radius of approximately 9.32 Earth radii and a mass of 5.6 Earth masses.
Fog layer blocks chemical analysis
The thickness of the detected haze can extend over a scale comparable to the radius of Terra, which represents one of the largest records observed in planetary atmospheres. Submicrometer Partículas, possibly similar to the tholins found on the moon Titã of Saturno, make up the layer at pressures between 1 and 100 microbar.
Atmospheric recovery models and forward simulations indicate a low metallicity atmosphere dominated by hydrogen and helium. The absence of clear absorptions in methane, water or other compounds reinforces the hypothesis that the haze acts as an opaque veil.
Scientists have considered alternatives such as the presence of tilted rings around the planet. However, this configuration would be short-lived, estimated at about 0.1 million years, making it less likely to explain current observations.
Unique features of the super-bloated planet
Kepler-51d orbits relatively close to its star, with a period of around 130 days and an equilibrium temperature close to 350 K.
The low density challenges traditional models of planetary formation. Hipóteses include massive envelopes of hydrogen and helium that represent more than 30% of the total mass or atmospheric inflation processes on young planets.
The Kepler-51 system contains two other transient super-puff planets and a fourth non-transient low-mass planet, identified by variations in transit time. Essas gravitational interactions helped refine orbital measurements.
Previous observations and evolution of the study
Data from Telescópio Espacial Hubble, collected at wavelengths close to infrared, already indicated signs of haze, but with limited coverage. James Webb expanded the spectral range, confirming the presence of a more extensive and dense layer than expected.
The host star, a young G dwarf, exhibits stellar activity with patches of higher temperature than those of Sol. Frações of coverage by spots varies between 0.1% and 10%, depending on the parameters assumed, but does not explain the slope observed in the spectrum.
Hypotheses about composition and formation
The composition of the mist may include tholins, soot or sulfur compounds, with particle sizes ranging from submicrometers to a few micrometers. Faint detection of methane at ppb levels suggests possible release from the interior but does not represent total abundance.
Researchers highlight that observations at longer wavelengths, with instruments like James Webb’s MIRI, could better map the extent of the haze or detect materials in hypothetical rings. Até the moment, haze remains the dominant explanation for the flat spectrum.
The study reinforces the uniqueness of the Kepler-51 system among the known ones, with multiple low-density planets challenging current theories.
