Planet was an early steam locomotive built in 1830 by Robert Stephenson and Company for the Liverpool and Manchester Railway.

The ninth locomotive built for the L&MR, it was Stephenson's next major design change after the Rocket.

[2] The Planet (from 1830) and the Patentee (from 1834, also designed by Stephenson) were the first locomotive types to be built in large numbers.

[3] The Planet locomotives appear closer to subsequent types, and conversely look quite different from Rocket although only a year separated these two designs (Stephenson's Northumbrian representing an intermediate evolutionary step).

Other improvements include: A working replica was built in 1992 by the Friends of the Museum of Science and Industry (MOSI) in Manchester, and is operated by volunteers to provide rides for visitors.