Kepler-78b: Mystery Exoplanet Shouldn't Even Exist

Kepler-78b may be an exoplanet notable for being approximately Earth-sized and likely possessing a rocky surface plus iron core, but that's where any similarity to our planet ends. It has an extremely tight orbit around sun-like star Kepler-78, completing one ‘year' in only 8.5 hours. It orbits so close in fact that the alien world's surface temperature soars to 2,000 degrees hotter than Earth's. Referring to Kepler-78b as a "rocky" world is therefore a misnomer - it's a hellish lava world.

But this is just a side-show to the real conundrum behind Kepler-78b: It shouldn't exist at all.

"This planet is a complete mystery," said astronomer David Latham of the Harvard-Smithsonian Center for Astrophysics (CfA) in a press release. "We don't know how it formed or how it got to where it is today. What we do know is that it's not going to last forever."

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To current planetary formation theories, this lava world is an abomination. There's no physical way a small world, only 20 percent larger than Earth, could have evolved in that location and there's no known mechanism that could have transported it there. But one thing that is certain, it can't stay roasting in that hellish orbit for long; it's destined to get swallowed by its star "very soon, astronomically speaking," said Dimitar Sasselov, also a CfA astronomer.

However, for a world that shouldn't exist, its life expectancy is pretty generous. Astronomers reckon that Kepler-78b will succumb to the star's tidal stresses and get ripped apart in about 3 billion years time.

When Kepler-78, which is located around 400 light-years away in the constellation Cygnus, was in the early stages of stellar development it would have been much larger than it is now. When astronomers calculated how big the young star would have been, Kepler-78b would be orbiting inside the star. "It couldn't have formed in place because you can't form a planet inside a star," said Sasselov.

So could the planet have formed in a wider orbit and migrated inward? This is another improbability, say the researchers. "It couldn't have formed further out and migrated inward, because it would have migrated all the way into the star. This planet is an enigma," Sasselov added.

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Despite its mysterious nature, Kepler-78b isn't alone. The world represents a new class of exoplanets recently discovered by NASA's Kepler Space Telescope. These worlds are small (approaching Earth-sized) with very compact orbits of less than 12 hours, but Kepler-78b is the first of this class to have its mass and density measured.

"Kepler-78b is the poster child for this new class of planets," said Latham.

Although Kepler originally detected Kepler-78b, the team used data from the high-precision spectrometer HARPS-North at the Roque de los Muchachos Observatory on La Palma and coordinated with a second, independent team using the HIRES spectrograph at the Keck Observatory, Hawaii. Whereas Kepler detects exoplanetary "transits" - as a world passes in front of its star, Kepler detects a slight dip in brightness - ground-based spectrometers measure the "wobble" of a star that is being gravitationally tugged by an orbiting world. A transit can be used to gain a measure of the physical size of the exoplanet, but the "radial velocity method" is required to reveal the mass of the world - using both measures, the planet's density can be derived.

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The astronomers note that it is entirely possible that a similar, star-skimming world existed inside the orbit of Mercury in our own solar system, only for it to have been swallowed long ago, leaving no trace.

While their origin, so far, is a mystery, perhaps this strange class of explanets should be called "Icarus Worlds," as, like in Greek mythology, they are flying too close to their suns; a cosmic dance that will ultimately lead to their demise.

Image: This diagram illustrates the tight orbit of Kepler-78b, which orbits its star every 8.5 hours at a distance of less than a million miles. It is only 2.7 stellar radii from the center of the star, or 1.7 stellar radii from the star's surface. Credit: David A. Aguilar (CfA)

Top Halloween Horrors of Alien Planets

Oct. 26, 2012 --

Exoplanets are mysterious, bizarre, but ultimately exciting. After all, with the help of the Kepler space telescope and advanced ground-based exoplanet-hunting techniques, for the first time we're directly observing a veritable menagerie of alien worlds. Through exoplanetary studies, we're beginning to even understand our place in the Universe. Despite all this fascination however, many of these alien worlds seem downright scary. Phantom worlds are on the prowl; ghosts dance in exoplanets' atmospheres; entire worlds are even getting ripped apart! Welcome to the world of Exoplanetary Horror, a rundown of the scariest alien worlds likely to frighten even Captain Jean-Luc Picard back into his shuttlecraft.

The Exoplanet Blowtorch The majority of exoplanets discovered thus far are gas giant worlds, often many times the size of Jupiter. Sometimes these worlds will orbit so close to their host stars that they are called "hot-Jupters." So, if you were an alien creature living in the gaseous atmosphere of one of these hellish worlds, where would you hide to get away from the searing heat? Well, you'd navigate away from the star, toward the night-side of the exoplanet, right? Bad move little floating alien! An exoplanet recently discovered by the Spitzer space telescope discovered a mysterious "hot spot" in its atmosphere, a full 80 degrees offset from the star. This means that the hottest part of the atmosphere isn't on the day-side (with the star directly overhead) but toward the night-side at sunrise and sunset -- where the temperatures exceed 1,000 degrees Celsius! That's hotter than molten rock! It is theorized that this extreme hotspot is caused by ultra-fast winds blasting like a blowtorch around the planet away from the star, generating shocks that boost atmospheric heating. So, unless you wanted to vaporize faster than a vampire bathed in sunlight, that's where you wouldn't want to be.

The Exo-Flying Dutchman One would think that the only thing that makes exoplanet Fomalhaut b scary is the fact that it orbits within a dusty cloud that looks exactly like the evil "Eye of Sauron" from the epic trilogy The Lord of the Rings. But no, the alien world is more subtle than that. It may not exist. Conflicting studies suggested that Fomalhaut b may be a ghost as it has exhibited strange movement not fitting with it being an exoplanet. But -- like the ghostly Flying Dutchman forever lost at sea, never to make it to port -- astronomers think they've spotted Fomalhaut b adrift in its ocean of dust once more. We'll have to wait and see until the world is either confirmed, or forever be a ghost story.

Pitch Black In the cult sci-fi horror flick Chronicles of Riddick: Pitch Black, anti-hero convict Riddick (Vin Diesel) crashes onto a rather unsettling alien planet infested with horrific flying bat-like creatures hell-bent on eating Riddick and the rest of the surviving crew. But it's not as simple as that -- these flying nasties only come out at night. Cue the screaming, running and killing... all in the dark. As Pitch Black proves: at night, horror comes out to play. And in the case of an exoplanet called TrES-2b, script writers' imaginations would run wild as to what sci-fi horror could be waiting deep in its inky atmosphere. The world is literally pitch black -- darker than coal. What's more, as it orbits so close to its star, TrES-2b is tidally locked, meaning one side of the exoplanet is in continuous nighttime. I wonder how Vin Diesel would deal with that.

But... It's Oozing Nobody likes stuff that oozes. Especially when it's oozing brain matter, blood, slime or some mystery extraterrestrial fluid that inextricably likes to cuddle its pray's face. So, on that note, welcome to 55 Cancri e! It's a whole exoplanet that -- you guessed it -- oozes. It could be the home world of The Blob, or perhaps a place where the Star Trek baddie Armus likes to vacation. But why is this world oozing? As this super-Earth exoplanet has such a tight orbit with its star and observations suggest there must be a huge quantity of some unidentified liquid inside its body, any fluids that appear on its surface will likely be solvents that have oozed from below.

The Exoplanet with the Melting Face Don't open the Ark of the Covenant! If you remember that famous "melting Nazi" scene from the classic Indiana Jones and the Raiders of the Lost Ark, you'll know exactly what I mean. The iconic scene included angry spirits, melting faces and the exploding head of Jones' nemesis Dr. René Belloq. At the time, it was cutting-edge horror animation, but imagine if you faced the rage of the Ark's spirits every... single... day. One world with a perpetual "melting face" is poor old CoRoT-2a, a world facing its own angry spirits from its host star in the form of powerful X-rays. The radiation is so strong that scientists using the Chandra space telescope think 5 million tons of material is being ripped from the world every second! If that's not a tortuous death, I don't know what is.

Bright Dancing Ghosts... Everywhere "I see dead people," said Haley Joel Osment in the 1999 ghost film The Sixth Sense when he broke the news to Bruce Willis that he has a rather unhealthy habit of seeing... well... dead people. It turned out that Willis was also [spoiler!] one of those dead people. Now, combine this with ancient folklore that said the aurora was in fact dancing souls of the dead (forget the aurora is, in reality, a beautiful side-effect of solar plasma raining through the upper atmosphere) and what do you get? We see dead people too! (It's a stretch, I know.) So, if the aurora is interpreted as the souls of the dead, spare a thought for what you'd see if you lived on an exoplanet with a global magnetic field, orbiting close to its host star. Scientists think that closely-orbiting "hot Jupiters" will experience awesome auroral displays as plasma from their nearby star floods their atmospheres. The result? Aurorae 100-1000 times brighter than the displays we see on Earth -- like ghosts dancing all over the planet.

The Loner Exoplanet Loners. Particularly weird loners with unpronounceable names. Carrying an axe. Hitchiking. Yep, that's scary -- a storyline that has been used for generations to scare the pants off cinema-goers. So, what about loner exoplanets? There are thought to be loads of exoplanets out there (an estimated 50 billion in our galaxy alone), but a few of them are too small and too distant from their host stars to be detected by conventional telescopes. However, sometimes, astronomers get lucky and spot one of these extra-solar loners. Take MOA-2009-BLG-266Lb for example. (Sounds like a weirdo, right?) It's a "super-Earth" that would normally orbit its star too far away to be spotted. But, with the help of general relativity, its 10-Earth mass bulk bends spacetime just enough to focus its star's light when seen from Earth. This is known as a "microlensing" event, and though rare, it can pick out tiny rocky worlds floating far from home. This exoplanetary loner might not be carrying an axe, but it is posing a lot of questions as to how it evolved so far away from its star.

Exoplanet Grows a Tail? When Jeff Goldblum grew spiky hair and other weird fly-like appendages in the human-experimentation-gone-wrong horror movie The Fly, needless to say, his friends grossed out. I'm sure exoplanet HD 209458b would sympathize with Goldblum's predicament. As it's orbiting close to its star, powerful stellar winds are stripping its atmosphere into space, creating a comet-like tail. HD 209458b must be wondering why its exoplanet friends are pointing, laughing and slowly backing away.

The Phantom Menace In a star system, far, far away, an exoplanet is being menaced by the gravitational pull of another world, causing it to slow down and speed up as it orbits its parent star... And yes, this is a real phenomenon, and not just a butchered opening for a Star Wars spin-off. Some 650 light-years away, an exoplanet orbits a sun-like star called Kepler-19. The world, Kepler-19b, has a very strange orbit in that sometimes it speeds up, completing its 9 day orbit 5 minutes fast, and at other times, it will complete an orbit 5 minutes slow. This orbital weirdness is all down to an invisible world whose gravitational influence is tugging at Kepler-19b. Astronomers know the phantom is out there, but have yet to find it...

Gates of Hell "Look out! You're about to get--" *BOOM* It's the classic cliffhanger -- there's an exoplanet, minding its own business, floating way too close to its parent star when, literally, all hell breaks loose. In the case of HD 189733b, located some 60 light-years from Earth, its star decided unleash a powerful flare that the Hubble Space Telescope was able to see. If you needed an example of the Gates of Hell opening, this is it. What's more, the exoplanet suffered horribly. Hubble was able to discern massive quantities of hydrogen blast from the exoplanetary atmosphere. By astronomers' reckoning, such powerful displays of star fury may explain why we've been discovering small rocky worlds so close to other stars -- perhaps they are the charred husks of what were once mighty gas giants. Nice. Exoplanetary corpses.

Back from the Dead? Zombies are awesome for chopping up, shooting or dismembering. And if we're to believe all those George Romero movies, no matter how you slice 'em and dice 'em, a zombie apocalypse is inevitable (unless you can destroy their brains quickly). So what has this got to do with exoplanets? Well, it depends how you interpret this little story, but it certainly sounds like we have a zombie exoplanet on our hands (figuratively speaking). Twelve years ago, astronomers using data from the Hubble Space Telescope thought they saw an exoplanet orbiting a star. On closer inspection, other astronomers couldn't find the world and declared the exoplanet dead. But in 2009, it appears the exoplanet, called TMR-1C, is back from the dead having been spotted by astronomers using the Canada-France-Hawaii telescope. OK, so it's not much of a zombie exoplanet -- and it's certainly not a reanimated corpse -- it was just hiding.

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A version of this slide show was originally published in 2011 and has since been updated.