Nasa's Kepler spacecraft has discovered a new planet while on its new K2 mission.

The discovery marks a comeback for the planet-hunting spacecraft after two of its four reaction wheels failed last summer.

The newly found planet, HIP 116454b, is 2.5 times the diameter of Earth and is smaller than Neptune. It follows a close nine-day orbit around a star that is smaller and cooler than our sun, Nasa announced in a statement.

"The Kepler mission showed us that planets larger in size than Earth and smaller than Neptune are common in the galaxy, yet they are absent in our solar system," said Steve Howell, K2 project scientist at Nasa's Ames Research Center in Moffett Field, California.

"K2 is uniquely positioned to dramatically refine our understanding of these alien worlds and further define the boundary between rocky worlds like Earth and ice giants like Neptune."

HIP 116454b is located about 180 light-years from Earth, towards the constellation Pisces and is too hot for living organisms.

Kepler's K2 mission began in May this year and the spacecraft has observed over 35,000 stars since then. It has collected data on star clusters, dense star-forming regions and several planetary objects within the solar system.

"K2 mission promises to not only continue Kepler's planet hunt, but also to expand the search to bright nearby stars that harbour planets that can be studied in detail and better understand their composition," the space agency said.

"K2 also will introduce new opportunities to observe star clusters, active galaxies and supernovae."