spaceSpace and Physics

This Strange Black Planet That Absorbs 99% Of Light Might Be The Darkest World We've Ever Found


Jonathan O'Callaghan

Senior Staff Writer

This is not the planet, just to clarify. There is no picture of it. sangriana/Shutterstock

Astronomer say they’ve found a planet that might be one of the darkest ever seen, one that absorbs almost 99 percent of light, making it blacker than charcoal.

A pre-print of the study describing the findings, led by Teo Mocnik at Keele University in the UK, is available on arXiv.


Called WASP-104b, the planet is located 466 light-years from Earth in the constellation of Leo. It is known as a hot Jupiter, as it is about 1.14 times bigger and 1.2 times as massive as Jupiter, and orbits its host star – a yellow dwarf – in an extremely tight orbit lasting just 1.76 days.

That orbit places the tidally locked planet just 4.3 million kilometers (2.6 million miles) from its star, only 4.5 percent of the distance from Mercury to our own Sun. As such, the clouds of the planet are thought to have been swept away by its star, leaving potassium and sodium in its haze layer to absorb incoming light.

At the moment, it’s not clear it’s the darkest exoplanet of all we’ve found so far. Mocnik told New Scientist he thought it was “top three”, along with TrES-2b and HAT-P-7b, which all seem to absorb similar amounts of light. So the margin of error in each discovery may dictate the darkest. The former was spotted back in 2011, while the latter described in December 2016 may also have winds of rubies and sapphires in its skies.

In their paper, the researchers note the lower estimate for WASP-104b's albedo (reflectivity) is 0.03, which is ”lower than the reflectance of charcoal.” This rules out any reflective clouds being present in its atmosphere. However, the planet probably glows more purple than black, owing to its immense heat.


The planet was studied by noticing the dip in light as it passed in front of its star, known as a transit. It was first spotted by the Wide Angle Search for Planets project in 2014, but follow-up observations by NASA’s Kepler telescope, which is running out of fuel, made this latest study possible.

Hot Jupiters normally reflect about 40 percent of starlight that hits them, so discoveries like this are quite rare. We’re finding a few oddities like this one though, and there are probably more out there.

(H/T: New Scientist)


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