NASA today revealed that its Kepler mission has discovered two new planetary systems that include three planets that might be what the space agency considers "habitable."

That term should be used loosely, however. What it really means is that the planets appear to have a surface temperature that might be suitable for liquid water, which is necessary to sustain life. Still, it's another step toward the discovery of a planet like Earth.

"The Kepler spacecraft has certainly turned out to be a rock star of science," John Grunsfeld, associate administrator of the Science Mission Directorate at NASA Headquarters in Washington, said in a statement. "The discovery of these rocky planets in the habitable zone brings us a bit closer to finding a place like home. It is only a matter of time before we know if the galaxy is home to a multitude of planets like Earth, or if we are a rarity."

The Kepler space telescope, which launched in March 2009, captures information about 200,000 stars every 30 seconds utilizing something known as the transit method.

"When a planet candidate transits, or passes in front of the star from the spacecraft's vantage point, a percentage of light from the star is blocked," NASA said. "The resulting dip in the brightness of the starlight reveals the transiting planet's size relative to its star."

This process has uncovered 2,740 possible planets; 122 have been confirmed.

The two most recently discovered systems are known as Kepler-62 (above) and Kepler-69 (below). Kepler-62 has five planets, and Kepler-69 has two. Of those seven planets, two of Kepler-62's are considered habitable, while one of Kepler-69's might be able to sustain life. They are known as Kepler-62e, Kepler-62f (above left), and Kepler-69c.

Kepler-62e: This was the first of the new planets to be identified. It's 60 percent larger than Earth and orbits its star every 122 days. That star, NASA said, is smaller and cooler than our Sun.

Kepler-62f: NASA said this planet is 40 percent larger than Earth, and likely has a rather rocky composition, based on previous studies of rocky exoplanets similar in size. It has a 267-day orbit and was found by Eric Agol, associate professor of astronomy at the University of Washington. He co-authored a paper on the discoveries for the journal Science.

Kepler-69c: This planet is 70 percent larger than Earth and orbits in the habitable zone of a star similar to our Sun. Its composition is unknown but its 242-orbit makes scientists think it might be similar to Venus.

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NASA's Kepler Finds 3 New Planets in 'Habitable Zone'