Forbes indicates Elon Musk of spaceX fame is worth $2 billion

Elon Musk joins our list of the world’s billionaires following a 25% stock value gain in Tesla, his publicly traded electric car company, since he appeared on our list of "Ones to Watch" in October. Meanwhile he is prepping SolarCity and SpaceX for IPOs. SolarCity will likely debut later this year, underwritten by Goldman Sachs, and is expected to achieve a valuation of $1.5 billion. Space transportation and innovation company SpaceX could be listed in 2013. Musk is working with fellow billionaire Paul Allen on a project that will launch unmanned rockets from what will be the world’s biggest plane