Since the spacecraft Kepler set out on a mission to learn more about Earth-sized and Earth-like planets in 2009, more than 150,000 objects in the Milky Way have been observed. One planet stood out; that planet is Kepler 37 b.

Kepler 37 b stood out because it is the smallest planet that has ever been discovered outside of our solar system. The planet is just a little bigger than Earth’s moon.

The spacecraft Kepler orbits our sun and looks at a mass of stars that is just off the left wing of a bird-like constellation called Cygnus. Kepler is designed to pick up small changes in the light that the stars emit.

Bert Pablo, graduate student at Iowa State who works with Kepler on data from these stars, said via email, “[Kepler’s] instrumentation is extremely sensitive to small changes in the light that comes from these stars. This is important because the main way it finds a planet is when it transits, or moves in front of a star.”

Astronomers were able to determine that this transit was being caused by the same planet each time because when they are being caused by the same planet, the change in brightness is the same, and the amount of time is the same for each transit.

According to a journal written about the Kepler mission on the NASA Ames Research Center website, “The scientific objective of the Kepler Mission is to explore the structure and diversity of planetary systems.”

Data from Kepler has been collected for about three years now, and observations will continue to be made on the planet until the end of the mission, which is expected to be about another seven years.

Kepler’s telescope also discovered three more planets that are orbiting Kepler 37 b, adding to the more than 100 new planets that the Kepler mission has already identified since its launch from Cape Canaveral Air Force Station in 2009.

In the future, observations on Kepler 37 b and its surroundings will probably have to be done from large telescopes on Earth due to the distance that the planet is from Earth.

Kepler 37 b is approximately 215 light years away from Earth, which means that any light observed from Earth now was was given off in 1798.

“The planet itself is so far away that we will never be able to send a probe there,” said Steve Kawaler, professor of physics and astronomy at Iowa State, via email. “Traveling even at the speed of light, it would take 430 years for a round trip.”

Despite not being able to send a probe onto the actual planet, Kepler and the large telescopes from here on Earth will be able to provide astronomers with enough information to make observations, and learn more about Kepler 37 b and other Earth-size, Earth-like planets for years to come.