WAIMEA, Hawai'i — The Keck Observatory has teamed up with NASA in one of the most ambitious space projects yet — the search for Earth-size planets in habitable orbits around stars in our galaxy.

NASA this week launched the unmanned Kepler space observatory into an Earth-trailing orbit a thousand miles away to gaze steadily at one patch of space in the Milky Way, focusing on the same 150,000 stars for 2 1/2 years. Kepler will be able to detect planets of roughly Earth's mass orbiting sun-like stars at "Goldilocks" distances — not too far, not too close — that might be capable of supporting life.

Once Kepler spots a likely planet candidate, University of California-Berkeley astronomer Geoff Marcy and his team at Keck will take a closer look, using the Keck I telescope and its high-resolution spectrometer to check the planet for habitable characteristics.

Marcy and his Keck colleagues have discovered dozens of giant planets — mostly larger than Jupiter in inhospitable orbits — around distant stars, but the arrangement with NASA and Kepler takes their planet-discovery venture into Earth-like zones.

The Kepler-Keck partnership will begin with observations from atop Mauna Kea during the last three nights of July, checking out any Earth-like candidates spotted by Kepler in its early look at the 150,000-star cluster.