Elon Musk is closing in on recapturing his title as the world's richest person, thanks to Tesla Inc.'s 70% rise this year. The disclosure comes as Musk, 51, has narrowed the gap to Bernard Arnault to less than $10 billion amid signs of growing demand for Tesla's electric vehicles. Much of Musk's wealth is still tied up in Tesla stock, though SpaceX has made up a bigger share in recent years.