“You know, our sun looks just like thousands of other stars in the sky. You’d never guess that there are planets going around it, and that one of those planets has people who consider themselves very intelligent. There would be no way of knowing that,” said Cornell University icon, astronomer Carl Sagan, in a 1973 interview with Rolling Stone, long before Michel Mayor and Didier Queloz announced the first discovery of a planet outside our solar system, an exoplanet, orbiting a solar-type star in our home galaxy, the Milky Way in 1995. The planet, 51 Pegasi b, a gaseous ball comparable with the solar system’s biggest gas giant, Jupiter was detected at the Haute-Provence Observatory in southern France, using custom-made instruments.
Could there be another planet in the universe with a society at the same stage of technological advancement as ours? Astrophysics initially wasn’t Ecole Polytechnique Federale de Lausanne physicist Claudio Grimaldi’s thing; he was interested more in the physics of condensed matter. Working at EPFL’s Laboratory of Physics of Complex Matter, his research involved calculating the probabilities of carbon nanotubes exchanging electrons. But then he wondered: If the nanotubes were stars and the electrons were signals generated by extraterrestrial societies, could we calculate the probability of detecting those signals more accurately?
Scientists are proposing seasonality of atmospheric ozone as a sensitive indicator of life in low-oxygen planets: “We are particularly excited about the prospect of characterizing oxygen fluctuations at the low levels we would expect to find on an early version of Earth,” says Timothy Lyons, a professor of biogeochemistry in University of Calfornia, Riverside, and director of the Alternative Earths Astrobiology Center. “Seasonal variations as revealed by ozone would be most readily detectable on a planet like Earth was billions of years ago, when most life was still microscopic and ocean dwelling.”
The Milky Way is nearly 14 billion years old, and its oldest stars developed in the early stage of the galaxy’s formation, making them about six to nine billion years old. They’re found in the halo, a roughly spherical component of the galaxy that formed first, in which old stars move in orbits that are highly elongated and tilted.
“As we improve our understanding of ancient Earth and the history of our solar system, perhaps we may someday uncover evidence that suggests the activity of another technological civilization right here in our neighborhood,” said Andrew Siemion, the director of Berkeley’s SETI Research Center.