Lunine

Although life on other planets has yet to be discovered, researchers continue to consider the possibility, said Jonathan Lunine, Cornell's David C. Duncan Professor in the Physical Sciences, April 18 at the 92nd Street Y in New York City.

They consider, for example, the Drake Equation, devised by Cornell astronomer Frank Drake in the 1960s. This calculation helps estimates the number of detectable extraterrestrial civilizations in the Milky Way galaxy, considering such factors as the fraction of stars with Earth-sized planets, the number of habitable planets per star and the number of new stars born per year.

Life in other areas of the cosmos has yet to be discovered, yet there has been progress in identifying other planets and moons in the solar system that might host life, said Lunine, a planetary scientist and physicist who researches how planets form and evolve, what processes maintain and establish habitability, how many known planets might harbor life and what types of environments might host life forms.

Space missions to those could lead to answers -- in some cases, within the next decade, he noted.

"Every year in our galaxy, a star like the sun is born," Lunine said. Surprisingly, with 200 billion stars in the Milky Way galaxy alone, only five are born each year. Stars are tracked and planets detected by NASA's Kepler spacecraft that identifies "transits," or the changes in light when a planet passes in front of its parent star.

"Today we know of 750 planets orbiting stars," Lunine said. "Kepler searches for the periodic dip in light of a star that is the signpost of a planet. It does this for 150,000 stars at the same time."

To find life on other planets, researchers look for signs of habitability, Lunine explained. On Earth, water would be an obvious element. However, is it possible, he asked, through the laws of physics and chemistry, that life could exist in elements other than those that make Earth a hospitable planet?

Lunine and his colleagues think so and have proposed a space mission to search for life on Saturn's moon Titan, one of the largest moons in the solar system. Evidence suggests a cycle of methane-generating processes there, which could be analogous to the Earth's hydrologic cycle.

The proposed Titan Mare Explorer would be the first nautical exploration of an extraterrestrial sea; if approved, it would leave Earth in 2016 and land on Titan in 2023 to sail the moon's largest lake, Ligeia Mare.

"This is the first opportunity in space exploration history to test for life in an organic-rich environment," said Lunine, who serves as a deputy-principal investigator for the mission.

Lunine wondered aloud whether Earth is unique to the cosmos. The possibility that there is life in outer space is intriguing, he said.

"Throughout history, humans have wondered if we are alone," Lunine said. "The possible existence of many inhabited worlds in the universe is inseparable from the issue of our place in the world and, hence, our own identity."

His talk was part of the Changing Earth seven-part lecture series at the 92nd Street Y in partnership with Cornell Plantations.

Claire Curry is a freelance writer in New York City.