What is the approximate minimum diameter required for an object to be classified as a planetesimal where self-gravity becomes the primary growth driver?
Answer
One kilometer or more
The transition from smaller accumulated bodies to a true planet builder involves overcoming the limitations of gentle sticking and gas drag. Objects that successfully survive this early phase grow large enough, typically defined as one kilometer or more in diameter, that their own internal gravitational field becomes significant. At this scale, self-gravity allows the body to noticeably influence nearby material, enabling it to actively attract and sweep up smaller dust and pebble-sized debris, marking the onset of planetesimal status.
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