There is more than one artist with this name:
1) Planet X are an American progressive fusion band that evolved in the USA from Derek Sherinian and Virgil Donati's collaboration on Sherinian's 1999 solo album Planet X.
Sherinian (keyboards) and Donati (drums) have remained the group's core members. Tony MacAlpine was featured on the first two studio albums, then left the band. Brett Garsed and Allan Holdsworth are featured on the latest Planet X album as guest musicians.