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When researchers look for a planet around a star, they only need to look at a small part of our sky. Not so for nearby objects. Plus, they can exploit the fact
by waserwill 8y ago
When researchers look for a planet around a star, they only need to look at a small part of our sky. Not so for nearby objects.
Plus, they can exploit the fact that stars with planets nearby will exhibit patterns of brightness, etc.,—if the planet is in the right orbit, has a great deal of mass, along with other parameters.
- daveFNbuck 8y agoAlso they're not usually looking for a specific planet around a particular star. The sky is full of stars and planets to find but there's only one planet nine.
- dotancohen 8y agoWhy do you assume that there is only one planet nine? Are you using the IAU definition of a planet? If so, why assume that there even is one? And if you are using a different definition, why assume that only one single object meets those criteria? If you are willing to forego "cleared the neighbourhood" then there might be dozens of round worlds with upwards of 10^20 KG mass in the solar system. We even know of such worlds not bound to any star at all!
- tobr 8y agoEven if there are multiple undiscovered planets, there would be at most one planet nine, plus maybe a planet ten, eleven, etc.
- dotancohen 8y agoWhat would happen if we discover an object that deserves the term "planet" at 180 AU, and then five years later discover another at 120 AU? Which one is "nine"?
- ahje 8y agoBoth. The one at 180 AU would be considered the 9th known planet from the Sun, until the one at 120 AU was discovered.