Scientists have confirmed the WASP-104b as the darkest planet ever discovered. The exoplanet was found in 2014 but scientists have just determined that it absorbs almost all of the light sent in its direction.

Researchers described the planet as "darker than charcoal."

Least-Reflective Planet Found

Researchers from Keele University in the UK published a paper in the Cornell University Library that shows just how dark WASP-104b can be. They found that it absorbs about 97 to 99 percent of light. In the description of the paper, the planet is called "one of the least reflective planets found to date."

WASP-104b is so close to its host star that it can complete its orbit in 1.75 days. It sits at a distance of 2.6 million miles from the star. Even with its proximity to its host star, it is able to reflect almost none of the starlight headed its way.

Co-author Ted Mocnik spoke to New Scientist about the study. He said that of all the planets that have been discovered, WASP-104b could be considered the top three darkest planets.

WASP-104b was discovered four years ago using the Kepler Space Telescope. Scientists used data from the Kepler Space Telescope's K2 Mission and were able to see that WASP-104b has a thick atmosphere made of atomic sodium and potassium. Both of these elements contribute to the planet's ability to absorb light. They both absorb light in the visible spectrum.

Hot Jupiter

WASP-104b is similar in size to Jupiter but it is much closer to its host star than Jupiter. These types of planets are known as Hot Jupiters. Hot Jupiters are gas giants with an orbital period of fewer than 10 days. This proximity to the host star makes them extremely hot. They're also tidally locked.

Most hot Jupiters are dark planets. ScienceAlert says that these types of planets reflect about 40 percent of the light that goes their way. There have been other planets that reflect almost as much light as WASP-104b.

In 2011, TrES-2b was discovered, orbiting around three million miles away from its host star. It reaches temperatures of about 1,800° F (980° C). It was found to reflect about only one percent of the light going in its direction.

In 2017, WASP-12b was observed to trap at least 94 percent of the visible starlight that fell into its atmosphere. Also a hot Jupiter, WASP-12b temperatures reach 4,600° F (2,540° C).

There are two theories on how hot Jupiters form. One theory suggests that the planet away from the host star, and that it migrated towards the host star later in life. The other theory suggests that hot Jupiters began as Super Earths which accumulated gas around the rocky layer. 

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