10 Planets that Shouldn’t Exist

Almost every year, astronomers discover planets that shouldn’t exist, prompting them to rethink their understanding of the way the Universe works.

Scientists and philosophers alike have long presumed that other planetary systems exist. However, until recent times, there was no way to detect these relatively tiny objects trillions of miles away that emit no light of their own. It wasn’t until 1992 when the first exoplanet was confirmed to exist. Since then, our journey of discovery has revealed thousands of exoplanets to date, and the number is constantly rising. Many of these planets are gas giants, because they’re easiest to detect. Others are rocky planets like those in the inner solar system. Others, however, have forced scientists to rethink their outlook on the Universe. Here are some of those bizarre alien worlds.

#1. PSR B1257+12

DraugrRon Miller NASA Blueshift

The first ever exoplanets to be discovered weren’t like anything in our solar system. In fact, they weren’t even orbiting a main-sequence star. PSR B1257+12 is a pulsar, a stellar remnant no larger than New York City yet 40% heavier than the Sun. This undead star, since named Lich, is all that’s left of a supernova explosion, the most awesome force of nature known. The discovery of three planets, Draugr and Poltergeist in 1992 and Phobetor in 1994 was baffling to the astronomy community. How could any planet survive a supernova explosion? It’s now assumed that they formed afterwards due to the collision of two white dwarf stars in the vicinity.

#2. Kepler-78b

Kepler-78bNASA/Ames/JPL-Caltech

Astronomers discovered the first Earth-like exoplanet in 2013. Kepler-78b is a rocky terrestrial world, but that’s where similarities end. Earning the nickname Planet Hell in the media, it orbits a Sun-like star some 30 times closer to its host than Mercury is to the Sun. Harvard professor Dimitar Sasselov described it as an abomination, a searing lava world that shouldn’t exist. With a year 8.5 hours long, its estimated surface temperature of 2,300°C makes Venus look like a winter wonderland. Current understand of planetary formation dictate that it can’t possibly have formed there, and there’s no known way it could have ended up there from beyond.

#3. Kepler-10c

For a rocky planet, Earth is on the large size, but the discovery of Kepler-10c in 2011 confounded astronomers who weren’t expecting to find a terrestrial world 15 times more massive and over twice the diameter of Earth. Again, this planet appears to completely disregard the known rules of planetary formation. With its great mass and, consequently, gravitational pull, it should have accreted any other matter in the area, ballooning into a gas giant like Neptune. Exemplifying an entirely new class of planet, the puzzling existence of this ‘Mega-Earth’ may be due to the gravitational pull of the relatively close star stripping away its gaseous envelope.

#4. HD 106906 b

HD 106906 bNASA/JPL-Caltech

One of the few planets to be directly imaged, HD 106906 b orbits at distance some 16 times further away from its host than Pluto is from the Sun. It’s believed to be about 11 times more massive than Jupiter, and it resides in a system that’s only 13 million years old, as opposed to almost 5 billion years for our own. Far away from the protoplanetary disc that orbits the young star, it seems impossible that that the gas giant formed there. Although there’s a tiny chance that it’s not even gravitationally bound to the star, it may have formed as part of a binary system or started life much closer to its host, but neither explanation is considered very satisfactory.

#5. Planet Nine

Planet NineCaltech/R

One of the most unusual planets might just be a member of our own solar system. Gravitational anomalies in the orbits of certain Kuiper Belt objects beyond Pluto can presently only be explained by the existence of a Neptune-like planet. Simulations suggest that the planet orbits between five and 18 times further away than Pluto with a highly eccentric orbit. Like HD 106906 b, it seems that Planet 9 could not have formed in the solar system itself. Instead, it may be a rogue planet captured by the gravity of the Sun or even a planet stolen from a passing exoplanetary system. Nonetheless, the existence of Planet 9 has yet to be confirmed.

#6. WASP-18b

With an orbital period of under a day, WASP-18b is a Jupiter-sized planet orbiting closely to its host star. Classed as a Hot Jupiter, this planet is being devoured by its host as tidal deceleration sends it hurtling ever closer to its burning fate. Already, its surface temperature is estimated to be over 6,000°C. Astronomers have not been able to figure out why the planet still exists, since the enormous tidal interaction should have already caused it to be devoured. After all, it seems like an incredible coincidence that we’ve discovered a planet right before its inevitable destruction or, perhaps, we need to reevaluate our understanding of tidal mechanics.

#7. TW Hydrae b

Protoplanetary discESO/L. Calçada

As exemplified by several entries so far in this list, we still have a rather amateurish understanding of how planets form. TW Hydrae b, which has yet to be confirmed, is a likely exoplanet orbiting a main-sequence star about 176 light years away. Its host star is between five and 10 million years old, a tiny baby in the world of stellar evolution. In fact, it’s so young that TW Hydrae b shouldn’t even exist yet, simply because it hasn’t had time to form from the protoplanetary disc. It’s also extremely far away from its host and also far away from the planet-forming dust of the protoplanetary disc. Perhaps, then, the planet was also captured from beyond.

#8. KELT-4Ab

KELT-4A Hypothetical Rocky PlanetM. Kornmesser / ESO

Imagine a world with three suns – that’s what an observer from a planet in the KELT-4 system would see every day. Originally assumed to be a normal binary system, astronomers later discovered that one of the pair was actually two stars in orbit of each other while, in turn, orbiting a single host. Like some of the other planets in this list, it orbits extremely close to its host KELT-4A. This unusual system may be the key to explaining how Hot Jupiters form in the first place – it was originally assumed that gas giants could only form in the outer reaches of their systems. However, the gravitational interaction of three stars might explain how it got so close to its primary.

#9. PSO J318.5-22

Rogue planetNASA, JPL-Caltech

Just as moons orbit planets, planets orbit stars, or at least that’s what we used to believe. The discovery of PSO J318.5-22 in 2013 shattered such assumptions by becoming the first known planet without any host at all. Planets cannot simply form from nothing in the emptiness of deep space, so this planet, which is about 50% larger than Jupiter, must have an unusual past. Stranger still, the planet’s luminosity and age indicates that its atmosphere is still extremely hot from its formation, consisting of molten iron rain and host dust. The best explanation for its existence suggests that it was kicked out of its original system shortly after its formation.

#10. 55 Cancri e

55 Cancri eNASA, Ron Miller

Orbiting some 25 times closer to its host than Mercury is to the Sun, 55 Cancri e is a scorching terrestrial world with a most unusual composition. It also bares the distinction of being the first exoplanet to have its atmosphere analysed. One popular hypothesis claims that the world might be rich in carbon which, under the extreme heat and pressures of the planet’s interior, would turn into diamond. Alternatively, it may be surrounded by an exotic state of matter known as a supercritical fluid, a substance that dissolves like liquids but otherwise has similar characteristics to a gas. Regardless, it remains one of the most peculiar exoplanets discovered to date.

Our understanding of planetary physics is constantly being challenged by an endless stream of surprises. I cannot even begin to imagine what sort of surprises we’re in store for, particularly with the upcoming launch of the James Webb Space Telescope next year. What bizarre things do you think we’re going to discover in the years ahead? Let me know in the comments below!

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