Kepler field of view (photo courtesy of Creative Commons).

According to a statement from NASA Tuesday, the planets "are too close to their star to be in the so-called habitable zone where liquid water could exist on a planet's surface, but they are the smallest exoplanets ever confirmed around a star like our sun."

The planets reside in a five-planet system called Kepler-20. They are approximately 1,000 light-years away in the constellation Lyra.

The Kepler space telescope detects planets and planet candidates. Ground-based telescopes and the Spitzer Space Telescope are then used to review observations on planet candidates.

According to the statement, the star field Kepler observes in the constellation Lyra can be seen only from ground-based observatories in spring through early fall.

Francois Fressin of the Harvard-Smithsonian Center for Astrophysics said the primary goal of the Kepler mission is to find Earth-size planets in the habitable zone.

"This discovery demonstrates for the first time that Earth-size planets exist around other stars, and that we are able to detect them," Fressin said.

Kepler-20e orbits its star every 6.1 days, Kepler-20f every 19.6 days. The statement said that these short orbital periods mean very hot, inhospitable worlds. Kepler-20f's surface temperature is 800 degrees Fahrenheit. Kepler-20e's is more than 1,400 degrees Fahrenheit, hot enough to melt glass.

Their parent star belongs to the same G-type class as our sun, though slightly smaller and cooler.

NASA announced the discovery of Kepler-22b on Dec. 5 that is in the habitable zone of its parent star.

"In the cosmic game of hide and seek, finding planets with just the right size and just the right temperature seems only a matter of time," said Natalie Batalha in the statement. Batalha is Kepler's deputy science team lead and professor of astronomy and physics at San Jose State University.

"We are on the edge of our seats knowing that Kepler's most anticipated discoveries are still to come."

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