As Kepler, the space observatory launched by NASA to discover earth-like planets orbiting other stars, marks its 1,000th exoplanet discovery, it discovers eight more planets that show potentially habitable conditions.

Although eight planets are newly confirmed, not all are said to be habitable. The new eight planets are either relatively small or orbit stars that are too cool and too small for life.

Three of these newly-validated planets are located in their distant suns' habitable zones. The range of distances from which is said to be where liquid water might exist on the surface of the orbiting planet, according to NASA.

And at least two of these newly discovered planets, Kepler 438-b and Kepler 442-b, are believed to have the rocky composition of the Earth.

The planet which is said to orbit a star in the constellation of Lyra, helped the scientists mark the millinery milestone after its validation as the most habitable and Earth-like planet found outside the solar system.

The planet which is named 438b Kepler is about 470 light years away from Earth and is slightly larger than Earth and completes the revolution around its sun in every 35 days, according to The Guardian.

Kepler was launched as part of NASA's Discovery Program, which is part of relatively low-cost science missions that estimate the number and the frequency at which Earth-like planets occur in the Milky Way Galaxy.

"Each result from the planet-hunting Kepler mission's treasure trove of data takes us another step closer to answering the question of whether we are alone in the Universe," said John Grunsfeld, associate administrator of NASA's Science Mission Directorate at the agency's headquarters in Washington.

Although Kepler has not discovered a true Earth-like planet, scientists believe that they're closer than ever to finding the Earth twins around other sun-like stars as the search continues with the $600 million Kepler project.