The first important result from the Kepler Mission about TrES-2b is an extremely low geometric albedo measured in 2011, making it the darkest known exoplanet.
If the entire day–night contrast were due to geometric albedo, it would be 2.53%, but modeling suggests that much of this is dayside emission and the true albedo is much lower.
It is estimated to be less than 1% and for best-fit model it is about 0.04%.
This makes TrES-2b the darkest known exoplanet, reflecting less light than coal or black acrylic paint.
It is not clear why the planet is so dark.
One reason could be an absence of reflective clouds such as those which make Jupiter so bright, due to TrES-2b's proximity to its parent star and the consequent high temperature.
Another reason could be the presence in the atmosphere of light-absorbing chemicals such as vaporized sodium, potassium, or gaseous titanium oxide; however, Kipping and Spiegel excluded heavy oxides of titanium and vanadium from their models, as it seems unrealistic that condensed, heavy compounds be present in the upper atmosphere.
They also note that in general, hot Jupiters are expected to be dark, because "absorption due to the broad wings of the sodium and potassium D lines is thought to dominate their visible spectra", and, apart from that of Kepler-7b (38±12%), albedo measurements for hot Jupiters have generally given only upper limits.
The first important result from the Kepler Mission about TrES-2b is an extremely low geometric albedo measured in 2011, making it the darkest known exoplanet. If the entire day–night contrast were due to geometric albedo, it would be 2.53%, but modeling suggests that much of this is dayside emission and the true albedo is much lower. It is estimated to be less than 1% and for best-fit model it is about 0.04%. This makes TrES-2b the darkest known exoplanet, reflecting less light than coal or black acrylic paint. It is not clear why the planet is so dark. One reason could be an absence of reflective clouds such as those which make Jupiter so bright, due to TrES-2b's proximity to its parent star and the consequent high temperature. Another reason could be the presence in the atmosphere of light-absorbing chemicals such as vaporized sodium, potassium, or gaseous titanium oxide; however, Kipping and Spiegel excluded heavy oxides of titanium and vanadium from their models, as it seems unrealistic that condensed, heavy compounds be present in the upper atmosphere. They also note that in general, hot Jupiters are expected to be dark, because "absorption due to the broad wings of the sodium and potassium D lines is thought to dominate their visible spectra", and, apart from that of Kepler-7b (38±12%), albedo measurements for hot Jupiters have generally given only upper limits.
TrES-2b