The Dark Planet

Last week Science Daily carried a report on the discovery of the darkest known exoplanet

The planet is TrES-2b a distant, Jupiter-sized gas giant, that reflects less than one percent of the sunlight falling on it, making it blacker than coal or any planet or moon in our solar system.

The discovery appears in a paper in the journal Monthly Notices of the Royal Astronomical Society.

"TrES-2b is considerably less reflective than black acrylic paint, so it's truly an alien world," said astronomer and lead author David Kipping of the Harvard-Smithsonian Center for Astrophysics (CfA).
In our solar system, Jupiter is swathed in bright clouds of ammonia that reflect more than a third of the sunlight reaching it. In contrast, TrES-2b (which was discovered in 2006 by the Trans-Atlantic Exoplanet Survey, or TrES) lacks reflective clouds due to its high temperature.

TrES-2b orbits its star at a distance of only five million kilometres. The star's intense light heats TrES-2b to a temperature of more than 1000 degrees Celsius -- much too hot for ammonia clouds. Instead, its exotic atmosphere contains light-absorbing chemicals like vaporized sodium and potassium, or gaseous titanium oxide. Yet none of these chemicals fully explain the extreme blackness of TrES-2b.

"It's not clear what is responsible for making this planet so extraordinarily dark," stated co-author David Spiegel of Princeton University. "However, it's not completely pitch black. It's so hot that it emits a faint red glow, much like a burning ember or the coils on an electric stove."

Kipping and Spiegel determined the reflectivity of TrES-2b using data from NASA's Kepler spacecraft. Kepler is designed to measure the brightnesses of distant stars with extreme precision.
The team monitored the brightness of the TrES-2 system as the planet orbited its star. They detected a subtle dimming and brightening due to the planet's changing phase.
TrES-2b is believed to be tidally locked like our moon, so one side of the planet always faces the star. And like our moon, the planet shows changing phases as it orbits its star. This causes the total brightness of the star plus planet to vary slightly.

Kepler has located more than 1,200 planetary candidates in its field of view. Additional analysis will reveal whether any other unusually dark planets lurk in that data.

TrES-2b orbits the star GSC 03549-02811, which is located about 750 light-years away in the direction of the constellation Draco.

Nothing to add form me except to say wow! Who knows what wonders and terrors lay out there in space.

Journal Reference:
1. Kipping D. M. and Spiegel D. S. Detection of visible light from the darkest world. Monthly Notices of the Royal Astronomical Society, 1–5 (2011)


Royal Astronomical Society (RAS). "Darkest known exoplanet: Alien world is blacker than coal." ScienceDaily, 12 Aug. 2011. Web. 15 Aug. 2011.