The Keck telescope at Mauna Kea, Hawaii

MAUNA KEA, Hawaii (CNN) -- Two new planets have been detected orbiting distant stars, bringing to 12 the number of worlds detected beyond our solar system.

Astronomers said Thursday the two planets could provide clues to how planetary systems are formed, and aid the search for extraterrestrial life.

"Make no mistake about it," said Geoffrey Marcy of San Francisco State University, who has helped find nine of the 12 planets discovered since 1995.

"What we're all about is discovering (planets) where evolution might have gotten a toehold."

They are the first planets discovered by the enormous Keck telescope in Hawaii, the sharpest optical telescope in the world. Marcy and a team that includes Paul Butler of the Anglo-Australian Observatory are using the telescope to scan more than 400 stars for the characteristic "wobble" caused by the gravitational effect of planets on stars.

No images of these new discoveries are available. In fact, scientists only know they exist because of the "wobble" detected in the motion of the stars they're orbiting.

Astronomer Steven Vogt describes one of the planets as "a real speedy son of a gun," orbiting its star once every three days. That planet is dubbed HD 187-123.

But the second planet may yield more valuable clues about the formation of solar systems and the universe. HD 210-277, which is about the size of Jupiter, has an Earth-like orbit.

The discovery of a dozen of these extra-solar planets in the past three years in no way diminishes astronomers' delight in each new discovery. Each one, Vogt said, is like a Rorschach test for the theorists, offering plenty of ways to look at this brand-new material and many new thoughts on the origins of the stars, their planets, their orbits and their life spans.

Reuters contributed to this report.