[identity profile] mmcirvin.livejournal.com 2011-02-25 09:09 pm (UTC)(link)
By modern informal naming conventions for extrasolar planets, Earth is presumably Sol b. Unless for discovery one needs realization that it really is a planet, in which case it's probably Sol g.

[identity profile] mmcirvin.livejournal.com 2011-02-26 02:23 am (UTC)(link)
The letters are assigned in order of discovery, starting with b. a is presumably the parent star, by analogy with the capital-letter designations for multiple stars, but nobody ever uses a.