A team of astronomers have discovered and confirmed 104 planets outside of our solar system using NASA’s Kepler spacecraft on its K2 mission. At least four of these have shown potential similarity to Earth, NASA confirmed Monday.

The discoveries were published online in the Astrophysical Journal Supplement Series after researchers combined data provided by Kepler with observations from telescopes based on Earth, primarily from the W.M. Keck Observatory on Mauna Kea, Hawaii, the Gemini telescopes on Mauna Kea and in Chile, the Automated Planet Finder of the University of California Observatories and the Large Binocular Telescope operated by the University of Arizona.

The exoplanets are all 20 to 50 percent larger than Earth by diameter. They are orbiting the M dwarf star K2-72, less than half the size of the sun. Their orbital periods range from five and a half to 24 days, even smaller than Mercury’s. Two of the exoplanets may experience irradiation levels from their star, 181 light-years away in the direction of the Aquarius constellation, comparable to those on Earth, NASA said.

For its initial mission, Kepler was programmed to survey a particular patch of the sky in the Northern Hemisphere. However, it lost its ability to focus on the target in 2013. A new mission, referred to as K2, was created for the telescope, providing it the capacity to observe a series of independent target fields in the ecliptic plane, which is the apparent path of the sun’s motion on the celestial sphere when seen from Earth.

kepler planets An artist's concept depicting select planetary discoveries made to date by NASA's Kepler space telescope. Photo: REUTERS/W. Stenzel/NASA

“Kepler’s original mission observed a small patch of sky as it was designed to conduct a demographic survey of the different types of planets. This approach effectively meant that relatively few of the brightest, closest red dwarfs were included in Kepler’s survey," Ian Crossfield, a Sagan Fellow at the University of Arizona’s Lunar and Planetary Laboratory in Tucson, leading the research effort, said in a statement, adding, "The K2 mission allows us to increase the number of small, red stars by a factor of 20 for further study.”

The latest discovery would provide great targets for NASA’s James Webb Space Telescope, the highly anticipated project scheduled to be released in October 2018, allowing “the astronomical community ease of follow-up and characterization,” according to Steve Howell, project scientist for the K2 mission at NASA’s Ames Research Center in Moffett Field, California.

“This bountiful list of validated exoplanets from the K2 mission highlights the fact that the targeted examination of bright stars and nearby stars along the ecliptic is providing many interesting new planets,” Howell said.