Almost 25 years after astronomers confirmed the existence of the first extrasolar planet ever discovered, there have been more than 3500 planets found orbiting stars other than our own. Among these are some worlds that might just be habitable, though there are others with environments far more extreme and skies more alien than anything in our own solar system. In this week’s listicle, we’ll be looking at some of the strangest extrasolar planets of all:
#1. COROT-7b – The Lava World
One of the smallest exoplanets discovered, COROT-7b is only 58% wider than Earth, but that’s where the similarities end. Orbiting so close to its host star, a yellow dwarf not unlike our own, its year is only 20 hours long. Baking in the intense light of its host sun in temperatures of up to 2600°C, it’s likely that the surface is entirely covered by molten rock. However, due its close proximity to the star, it’s likely to be tidally locked, meaning that the one side of the planet always faces the sun, leaving the other side in permanent cold and darkness. If you were to stand on the surface of COROT-7b, the sun’s light would also blind you in an instant.
#2. 55 Cancri e – The Diamond World
Almost nine times heavier than Earth, 55 Cancri e has the exotic distinction of being a diamond planet. It is assumed from observational data that about a third of the planet’s mass is carbon. Due to the planet’s close proximity to the star and the intense heat and pressures from its interior, it is suspected that this carbon has turned into diamond. However, recent speculations have led astronomers to believe 55 Cancri e might be even odder than originally assumed. It is one of the very few exoplanets to have its atmosphere explored to reveal hydrogen, helium and hydrogen cyanide. With a surface temperature of around 1700°C, it’s also pretty hot!
#3. HD 189733b – The Molten Glass World
HD 189733b is an enormous gas giant even larger than Jupiter. It orbits close to its host star and boasts a surface temperature of around 1000°C. It is home to one of the most brutal environments of any planet ever discovered. In fact, it’s so harsh that it makes even the scorching surface of Venus look hospitable. Aside from its raging temperatures, the upper atmosphere of HD 189733b experiences winds of over 4,000 mph (6437 kph), or some 5.5 times faster than the speed of sound. It also rains molten glass sideways. From indirect observations, astronomers have deduced that the world is a deep azure colour.
#4. HD 188753 Ab – The World with Three Suns
Sometimes nicknamed Tatooine after the planet in Star Wars, HD 188753 Ab, like its namesake, has three suns. Experiencing the most exotic sunsets and sunrises of any planet so far discovered, the view would undoubtedly be spectacular. HD 188753 Ab, is suspected to be a gas giant about the size of Jupiter. It orbits close to its primary host star, and its year length is just over 3 days. However, since there have been no further confirmations of the planet’s existence since the initial report in 2005. Nonetheless, it’s likely that there are plenty of other such exotic worlds, since binary or even triple star systems are much more common than previously thought.
#5. WASP-12b – The Doomed World
44 times closer to its host star than Earth is to the sun, WASP-12b truly is a doomed planet. Sporting a radius about three times that of Jupiter, this enormous, searing hot gas giant world is so close to its star that it’s literally being devoured. The immense gravitational pull is in the process of tearing the planet apart as at makes a full orbit in little over 24 hours. As the atmosphere of this giant world is sucked away by the raging furnace that is its sun, it creates a spectacular ring of debris around the star. NASA estimates that the remaining mass of the doomed world will have been sucked away entirely within 10 million years.
#6. GJ 1214b – The Water World
GJ 1214b has the interesting distinction of being the most likely candidate for a water world with a liquid ocean encompassing its entire surface. The enormous global ocean would cover a globe several times larger than Earth, but only about half the size of Neptune. Since it’s much closer to its host star than Earth, surface temperatures are likely to be in the region of 100 to 200°C, depending on the planet’s atmospheric makeup. Since any global ocean on GJ 1214b would be thousands of miles deep, intense pressures lower down would lead to some truly exotic forms of water, such as high-pressure ices and even plasma phases.
#7. Kepler 452b – The Habitable World?
Ever since the first exoplanets were discovered in the early nineties, the quest to find Earth 2 has been in full swing. There have already been nearly a dozen exoplanets discovered orbiting in the so-called Goldilocks Zones of their host stars, where they’re at the right distance for the surface to be the right temperature to host Earth-like life. The most promising of these discoveries so far is Kepler 452b though, unfortunately, it would take some 26 million years to get there with today’s technology. However, Kepler 452b is well within the habitable zone, it’s about 60% bigger than Earth and has a year of 385 Earth days. It orbits a G-class star like our sun.
#8. PSO J318.5-22 – The Lonely World
Some planets don’t even have host stars and instead drift through space alone, never experiencing any sunrises or sunsets. Due to their nature, they are very hard to find, though there have been some exceptions like PSO J318.5-22. However, unlike most exoplanets, this one has been imaged directly, since it is rather large at six times the mass of Jupiter. Nonetheless, it’s too small to sustain nuclear fusion so, like Jupiter, it could never have become a star. Very little else is known about this planet, but it’s likely to be a cold, dark world that probably drifted away from its host star system when it was young.
#9. TrES-2b – The Dark World
The darkest extrasolar planet ever discovered, TrES-2b was identified in 2011 as a gas giant of similar size and mass to Jupiter. Orbiting close to its host star, it’s classified as a hot Jupiter. The oddest thing about TrES-2b, however, is that it reflects less than 1% of the light of its host star, making it almost as invisible to the naked eye as a new moon. As such, the surface has the reflectivity of black acrylic paint. The reasons for this odd trait remain unclear, though it may be due to a large amount of light-absorbing chemicals in its atmosphere or a lack of reflective clouds like those of the gas giants in our solar system.
#10. Draugr – The Aurora World
When it comes to looking up at the night sky, Draugr (also designated PSR B1257+12 A) perhaps offers the most spectacular views of all. This small, rocky world orbits a pulsar, a highly magnetised type of stellar remnant that is only a few miles wide but weighs much more than the entire Earth. As such, the same forces that cause the Aurora Borealis on Earth are at play on Draugr, albeit many times more spectacular. No matter where you were on the surface of this lonely world, the aurorae would dominate, and the sun would look like a tiny but intensely bright point of light with huge beams spinning around like a lighthouse, yet much faster.