‘Pitch black’ planet is one of the darkest ever discovered

Researchers from Keele University have discovered a planet that absorbs 99% of light, making it one of the darkest planets ever found. 

The planet, named WASP-104b, was discovered by a team from Keele’s Astrophysics Group, who used NASA’s Kepler telescope to show that it is ‘darker than charcoal.’ 

Lead researcher Teo Močnik explains: “This is one of the darkest planets ever discovered - reflecting very little light from its host star.”

Močnik, who is a researcher at Keele University working with Professor Coel Hellier and Dr John Southworth on the search for transiting extra-solar planets, explains why this is unusual:

“WASP-104b is interesting because it was not even seen. All planets reflect starlight from their host star. Some planets are highly reflective, such as Venus reflecting 70% of the light, while some others reflect only 10%.

“When analysing the highly precise photometric data from Kepler, we were surprised not to see reflected starlight from WASP-104b.”

The planet was discovered orbiting a yellow dwarf star some 470 light-years away from us in the constellation Leo, and is categorised as a ‘hot Jupiter’ planet. Hot Jupiters are gas giant planets of a similar mass to Jupiter, but are located much closer to their host stars - making them very hot. WASP-104b is so close to its host star (at around 2.6 million miles) it takes just 1.76 days to complete its orbit.

This proximity to its host star may be the reason the planet is so dark - as conditions are too hot for clouds (which are highly reflective) to form. The lack of light being reflected from the planet may also be attributed to the presence of alkali metals such as sodium and potassium in a ‘hazy’ atmosphere, which causes significant absorption of light in the visual wavelengths.

Močnik added: “Since WASP-104b is one of the least-reflective planets known to date, it will serve as a test bed for atmospheric models.”

The study has been published in the pre-print resource arXiv, and is awaiting peer review.

The Astrophysics Group at Keele University operates the WASP-South robotic telescope in South Africa, which is the world's most successful ground-based search for transiting extra-solar planets, having discovered the majority of the transiting exoplanets in the Southern hemisphere.

Astrophysics Group members are also experts in measuring the properties of transiting planets and their host stars, detecting planetary atmospheres, and identifying thermal emission from the hot daysides of the planets.

Image credit: NASA