The Argentine spoke from his Vatican desk facing a wide-screen television on which astronauts from the US, Russia and Italy could be seen floating together in their blue suits.

"Astronomy makes us think about the universe's boundless horizons and prompts questions such as 'where do we come from, where are we going?'" Francis said.

He then asked about the astronauts' opinion of love as a force that moves the universe and what was their source of joy up in the space station?

Space, the final frontier

The 30-second delay in the satellite feed gave the astronauts — Italian Paolo Nespoli, Americans Vande Hei, Randolph Bresnik and Joseph Acaba, and Russians Sergej Nikolaevic Rjazanskij and Alexandr Misirkin — time to ponder the questions and how they would manage without a Russian translator.

Of the three Americans, one is a Baptist and two are Catholics, both Russians are of the Orthodox faith and the Italian is a Catholic, the Vatican said.

To boldly go

"I get the most joy by looking outside every day and seeing God's creation, maybe a little bit from his perspective," Bresnik said, adding that the visible thinness of the planet's atmosphere showed how fragile life on Earth is.

Nespoli - on his third trip into space - said that despite the bird's eye view of Earth he remained perplexed. "Our aim here is to spread knowledge, (but) the more we learn, the more we realize we do not know."

"I would like people like you, theologians, philosophers, poets, writers, to come to space to explore what it means to be a human in space," Nespoli went on.

Francis nodded and smiled in response, after a 30-second delay.

Far from wars, famines, pollution or human folly, Nespoli said: "The future of humanity looks better from up here." He added that he was ill-equipped to reflect on the destiny of humanity.

He then thanked the pope for "making us think about things that are bigger than us."

Second Vatican to ISS phone call

The first pope to talk with astronauts in space was Benedict XVI in 2011. He rang the ISS — which has been continuously occupied since 2000 — when Nespoli was also among the crew.

The ISS is a spacecraft orbiting at a distance of 400 kilometers (248 miles) above the Earth, and has hosted multinational teams since 2000. Their main task is to carry out scientific experiments.

jbh/kms (AFP, dpa)