Joby Aviation stock plummeted Thursday after surging 28% Wednesday following Toyota announcing an additional $500 million investment into Joby Aviation, bringing the legacy automaker's total stake in Joby to more that $890 million to support the commercial production of the startup's electric air taxi. Shares of Joby declined 8.7% to 5.61 during Thursday's market action. On Wednesday, Joby Aviation stock rocketed 28% to 6.14.