According to the International Astronomical Union (IAU) a planet should clear its orbit of other objects. This condition was a source of heated debate among astronomers that rages on to this very day. It was this alienating third criterion that dethroned Pluto and other dwarf planets from planetary status.
So when I heard that KOI-730's exoplanets were sharing orbits, my first reaction was, “Hey wait a minute...if we try to apply the ‘official’ definition of 'planet' to these exoplanets, they would not be planets at all!”
This is just one instance, but i'm sure there are many derivatives of the case of KOI-730's co-orbiting exoplanets that "share" orbits with other objects. Think of intersecting resonant orbital paths, or locked LaGrangian exoplanet orbits, or exoplanets still in the process of clearing out debris in their path. (It would take millions of years for young planets to clear their orbital zones, mind you.)
I’ve always thought that exoplanets are planets. But today, I'm rethinking that. Yes, exoplanets continue to surprise us, and it's for that reason that I once concluded, Exoplanet is the new 'Planet' by virtue of the awe and wonder that they instill upon us. But now, I’ve come to another realization: Exoplanets are not Planets, and that is liberating. It frees the mind from a limited way of thinking, because the mindset needed for understanding exoplanets is different. Exoplanet discoveries forces you to unlearn, and it frees your mind from the confines of your own star system. Exoplanets require a novel way of thinking. And that is why I love exoplanets so much. They make us think in new ways. Exoplanets make us think outside the sphere! And all that is possible because of Science.
It frustrates me when some astronomers deny dwarf planets of being planets, and yet speak of exoplanets as planets in a carefree way. I want to avoid being annoyed by such inconsistent mindset. So I am letting go of the debate about planets. (Of course, I still consider dwarf planets as legit planets) I will simply let planets be planets, and exoplanets be exoplanets. Just that. I will not try to make exoplanets fit in as planets. I will not even attempt to redefine what a planet is, or grumble about its flawed definition. In fact, I'd rather we keep the current planet definition the way it is now. Let it be a reminder, a tainted bygone--an old ugly chapter in the history of Astronomy.
Perhaps someday, a new definition of the planet will emerge, one that is more universal, that will encompass exoplanets as well. But for now, we are experiencing a temporary chaos brought about by the "growing pains" in our effort to understand the universe.
But until then, with the narrow-minded planet definition we have arrogantly locked ourselves into, who can say with certainty that exoplanets are planets?
This is a new era of planetary thinking. Humanity’s concept of the Planet is of the past, but Exoplanets are of the future.
Links:
NewScientist: Two exoplanets found, sharing one orbit
Life, Unbounded: Make Me a Planet
Theories of Planetary Formation, Busted
Exoplanet is the new 'Planet'
