Kepler Spacecraft Finds New Exoplanets

NASA's Kepler spacecraft has discovered six exoplanets orbiting a star named Kepler-11, which is about 2,000 light-years away. 

Kepler-11 is a yellow dwarf star, like our Sun.

All of the planets in the Kepler-11 system are made up of mixtures of rock and gas and are larger than Earth. The largest ones are about the size of Uranus and Neptune.

They are some of the smallest exoplanets that have been discovered so far.

Kepler-11's five innermost planets (Kepler-11b through Kepler-11F) are closer to their star than Mercury is to our Sun.

The orbit of the outermost planet (Kepler-11g) is about half the distance from its star as Earth the distance from Earth to the Sun.

The Kepler spacecraft has also found more than 1,200 other objects that may be exoplanets, as well. 68 of these objects are about the same size as Earth, and 54 are in their stars' habitable zones - at the right distance from the star for water to exist on the planet in a liquid state.

Five exoplanet candidates are both in their star's habitable zones and similar in size to Earth.

Currently, about 500 exoplanets have already been discovered.

The smallest exoplanet that has ever been found is Kepler-10b.  This planet was also discovered by the Kepler spacecraft.  Kepler-10b is the first rocky exoplanet to have been discovered. It orbits a star called Kepler-10, which is about 560 light-years away from Earth.

Kepler searches for exoplanets by measuring changes in the brightness of stars. When a planet passes in front of a star, it temporarily blocks some of the light from the star, making the star seem slightly dimmer. The planet's movement in front of the star is called a "transit". Kepler can determine the size of a potential planet by measuring how much the brightness decreases, and convey information about the planet's orbit by determining how often transits occur.

The Kepler spacecraft  has a special telescope, known as a "photometer", that continually monitors the brighteness levels of  more than 100,000 stars.

About 170 stars that have been studied by the Kepler spacecraft may be orbited by multiple planets.

NASA will make further studies to determine if the new exoplanet candidates are actual exoplanets.