Impossible Newly-Discovered Exoplanet Defies All Theories On Planet Formation

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Looking for planets is much harder than looking for stars, but it has the potential to produce far more compelling results; a star is a ball of fire, true, but planets can be so much more diverse.

The relatively new and still novel process of looking for planets has already gifted astronomers with headlines about planets made of diamond, or with oceans of liquid oxygen, or which rain sulfuric acid. These are intrinsically interesting things, more relatable than sunspots or solar flares, but they all have one thing in common: while these new and distant planets may be amazing, even their most alien features conform to the basic principles of science.

Now, a research team led by a graduate student at the University of Arizona has spied a planet further out than any other in a sun-like system, and it has many astronomers baffled. There were two things immediately puzzling about it: its mass, which came in at an immense 2 × 1025 metric tons. That’s roughly 11 Jupiters, or, put differently, one one-hundredth the mass of the sun. Its orbit was also of note, roughly 650 times bigger across than Earth’s. According to everything astronomers think about planet and star formation, a planet as large as that ought not to have been able to form so far from its host star. This enigmatic giant is orbiting star HD 106906 and defying what astronomers know about the origins of planets.

The main theory of how planets form involved the accretion of small bodies like asteroids to slowly form planets. That’s how the close-in planets like Earth formed, with a chaotic field of debris and gas particles slowly collapsing into progressive fewer and more massive bodies. Further out, though, the material becomes too diffuse to make planets of any real size. Our furthest large planets are Uranus and Neptune, which orbit at a paltry 15-30 times the average Earth-Sun distance. This planet is dozens of times their size, and hundreds of times further from its star.

Some theories about how it could have gotten so large so far out have been bandied about, but there are problems with them. One says that the planet is a failed attempt at a second star, making it a stillborn binary system. The problem is, ironically, that the planet isn’t big enough for that to make sense, since binary formations usually don’t exceed a 10-to-1 mass ratio. This planet (planet ‘b’ in the HD 106906 system) is less than one percent as large as its host star, making the ratio far off predictions.

Another possibility is that the planet formed traditionally around a completely separate star and was then wrenched free in some unimaginably powerful event. It’s a nice idea, and one that makes the planet seem particularly lonely. It’s at least warm, still glowing with heat from its formation and maintaining surface temperature of a toasty 1,500 degrees Celsius. The problem here, though, is that the planet is still very young, less than 13 million years old – not nearly enough time for such a large planet to form, break away, and fly to a nearby system for pick-up.

The search for exoplanets is constantly providing new evidence to extend the borders of our understanding. Astronomers have already found planets that refine their understanding of planetary formation and the weird places it can occur. Much like biological evolution, the physical evolution of the universe is occurring on such an enormous scale that extreme oddities are bound to pop up here and there.
Almost as pressing as the question of how this planet formed is the question of just how common it is. Have we found a whole new class of planet that demands a robust explanation, or is this an extreme freak of nature that shows the variety possible in the universe?

Only time will tell, but with significant research gearing up for this planet it really should not take long to figure it out.

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“Impossible Newly-Discovered Exoplanet Defies All Theories On Planet Formation”