Jesuit priest Jose Gabriel Funes, director of the Vatican's astronomic observatory, says star-gazing brings him closer to God.

"I became an astronomer in order to get closer to God who created the universe," said Funes at the observatory in the vast park surrounding the pope's summer residence in Castel Gandolfo, near Rome.

"We wonder the same things that our secular colleagues do -- how does the universe work, how did it originate, are there planets similar to Earth?" said Funes, 47.

Both Funes and his colleague Guy Consolmagno studied astronomy before joining the priesthood.

"I'm primarily a scientist," said Consolmagno, previously a university professor in the United States.

"It's my belief in God that gives me the courage to do science because I have to have a faith... that there are answers, that there are laws to be found, that the universe is worth studying, it's not just chaos," he said.

"Where I actually experience God is in the joy, in the delight when the numbers suddenly make sense, when the theory works," he added.

The observatory Funes has run since 2006 is housed in a former monastery on the edge of the papal sprawl, a fitting location suggesting the intersection of faith and science.

"But we are the pope's observatory. We are here to serve the pope, the Church and our colleagues," Funes said, adding: "The Church has always been interested in astronomy."

Centuries ago, papal astronomers combatted theories seen as dangerous -- such as those of Galileo Galilei, who had the temerity to claim that the Earth revolves around the Sun.

But all that seems far away here, where the second edition of Galileo's "Dialogue Concerning the Two Chief World Systems" -- banned by the Inquisition in 1633 -- is displayed with pride.

The simple one-storey facility's work has been limited to research and teaching since 1981, when the observatory set up a telescope in Tucson, Arizona, because of the purity of the sky there.

-- I experience God when the numbers make sense --

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An older telescope is still used in the papal residence to observe nearby planets.

The Tucson observatory has earned the attention of the world scientific community.

It proved the existence of the so-called green flash, an optical effect visible at the setting of the sun in the sea when there are no clouds.

"We showed that it wasn't subjective, that it could be observed and photographed," said the Argentinian Funes.

As a man of science, Funes is "not worried about the possibility of extra-terrestrial life," he said.

The Catholic Church does not have an explicit doctrine on the complex question.

"There is no proof of extra-terrestrial life so far, but in a universe that is so huge with a hundred billion galaxies that each have billions of stars, some of them could have characteristics similar to Earth's..." said Funes, his voice trailing off.

In Consolmagno's office cum lab, he is currently studying a meteorite that he described proudly as the "only vestige of a star that disappeared 4.5 billion years ago."

But the most precious object at the Observatory is a fist-sized rock from Mars, which is black on the outside and green -- not red -- within.

"There aren't many that as so big, and collectors would pay 1,000 euros (1,300 dollars) a gramme!" Consolmagno said, cradling the rock in a rubber-gloved hand.