Astronomical evidence
HD 189733 b is a hot giant with a catalog orbital period of about 2.22 days. Its blue optical appearance was investigated by observing the combined light of the star and planet before, during and after the planet passed behind the star. This event is a secondary eclipse. When the planet disappears, its contribution to the system’s brightness is removed. Comparing that change across visible wavelengths allowed the Hubble team to isolate a blue reflected-light signature. The method measures unresolved light; it does not require a detailed image of the planetary disk. A blue signal is not evidence for an ocean. Atmospheric scattering and absorption can produce a blue appearance in a strongly irradiated gas giant. Silicate particles are part of the physical interpretation, while the exact distribution of clouds remains a separate question.
The illustrated viewpoint
The image’s cobalt swirls, curved limb and nearby platform translate those broad ideas into a fictional view. Individual vortices, viewing altitude and visible brightness have not been reconstructed from the eclipse measurements.
The image’s cobalt swirls, curved limb and nearby platform translate those broad ideas into a fictional view. Individual vortices, viewing altitude and visible brightness have not been reconstructed from the eclipse measurements. All depicted life and technology are fictional.
Catalog measurements & sources
Host: HD 189733. Snapshot: 25 September 2026. Errors, limits and source provenance are retained. Calculated values and model estimates are not direct measurements. Unknown is not zero; equilibrium temperature is not surface temperature.
| Quantity / unit | Value / reported errors | Source |
|---|---|---|
| Radius · Earth radii | 12.6662 (+0.11209 / -0.11209) | Stassun et al. 2017 |
| Mass · Earth masses | 359.148 (+25.4264 / -25.4264) | Stassun et al. 2017 |
| Density · g/cm³ | 0.943 (+0.024 / -0.024) | Agol et al. 2010 |
| Orbital period · days | 2.21858 (+1.5e-07 / -1.5e-07) | Stassun et al. 2017 |
| Orbital semimajor axis · AU | 0.03126 (+0.00036 / -0.00036) | Rosenthal et al. 2021 |
| Eccentricity | 0 | Stassun et al. 2017 |
| Inclination · degrees | 85.71 (+0 / 0) | Stassun et al. 2017 |
| Irradiation · Earth flux | 356 (+13 / -12) | Addison et al. 2019 |
| Equilibrium temperature · K | 1209 (+11 / -11) | Addison et al. 2019 |
| Stellar effective temperature · K | 5052 (+16 / -16) | Stassun et al. 2017 |
| Stellar radius · Solar | 0.75 (+0.01 / -0.01) | Stassun et al. 2017 |
| Stellar mass · Solar | 0.79 (+0.08 / -0.08) | Stassun et al. 2017 |
| Stellar luminosity · log Solar | -0.46119 (+0.01798 / -0.00876) | Barstow et al. 2017 |
| Stellar age · Gyr | 1.4 (+4.9 / -1.9) | Southworth 2010 |
| Stellar metallicity · dex | -0.02 | Stassun et al. 2017 |
| Distance · pc | 19.7638 (+0.0128 / -0.0127) | TICv8 |