Strange Alien Planet is Black as Pitch

Fagjun | Published 2017-09-29 17:57

Scientists found that a large alien planet is pitch black, absorbing almost all the light that hits its surface.


Artist's impression of WASP-12b and its host star [Image by NASA, ESA, and G. Bacon (STScI)]



This planet is WASP-12b, an exoplanet that was discovered in 2008 by the SuperWASP planetary transit survey. It orbits WASP-12, a yellow dwarf star similar to our sun in mass and radius, in the constellation Auriga. WASP-12b completes its orbit around the star in just a little over one Earth day, and its distance from its host star is 1/44th the distance of Earth from the sun. The planet is also twice the size of Jupiter, and is classed as a “hot Jupiter” because of its close proximity to its star.


This close proximity has also made WASP-12b a strange, “hellish” world. It has warped into an egg shape due to WASP-12's strong gravitational pull. Like many other close-orbiting planets, WASP-12b is tidally locked to its star, which means only one face of the planet is constantly turned to the star.



A Low Albedo


Comparison between Jupiter and WASP-12b [Image by Aldaron, a.k.a. Aldaron - Own work, incorporating public domain images for reference planets (see below), inspired by Thingg's size comparison, CC BY-SA 3.0]



Astronomers have been studying the strange alien planet since its discovery in 2008. However, it was only recently that they made a compelling discovery about WASP-12b. The researchers were surprised to find that the planet has a very low albedo, which indicates how reflective the surface of a planet or moon is. At most, WASP-12b's albedo is 0.064.


Just what does this mean? To better understand how low the planet's albedo is, let's compare it to the albedo of Earth and two different moons. Earth's albedo stands at 0.37. Our moon's albedo is 0.12. Meanwhile, Enceladus, one of Saturn's moons, has an albedo of 1.4. Enceladus is actually the most reflective object in our solar system.


WASP-12b's albedo of 0.064 makes it darker than asphalt. This measurement gives us a better idea of what the planet looks like.


Astronomers watched as WASP-12b passed behind of its star, during which they tried to deduce the planet's color. The perpetual daylight side of the planet showed that the surface reflected almost no light at all. The planet absorbed about 94% of the light that touched it. Researchers note that many other hot Jupiters are also quite dark in color, though their surface temperatures are much lower than those of WASP-12b.



The Hellish Alien Planet


An older illustration of WASP-12b and WASP-12, before scientists discovered the planet's color [Image by NASA/JPL-Caltech]



Other dark hot Jupiters may have clouds and alkali metals that facilitate the absorption of light. However, this is not the case with WASP-12b, which makes the planet quite unique. At a temperature of 2,500°C on its daylight side, the planet is incredibly hot. Temperatures this high break molecular hydrogen down to atomic hydrogen.


Also, clouds cannot form on the daylight side, leaving those molecules unprotected from the heat of the host star. The researchers' findings show that the atmosphere of WASP-12b is mostly made of atomic hydrogen and helium. This combination results in the planet being pitch black, especially since atomic hydrogen absorbs more light than molecular hydrogen.


This strange alien planet may appear pitch black to us, but scientists also say that if you approach the planet and look at it up close, it would appear red-hot like metal on the forge.

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