I recall a poster in a science classroom depicting a radiant blue, white and brown orb afloat in the darkness of space: our beloved and much abused home, Earth. The poster was emblazoned with the slogan: “Good Planets Are Hard to Find!” A recent astronomical discovery would seem to contradict this fetching claim.
A research paper by UC-Berkeley graduate student Erik Petigura and co-authors published on November 4 in the Proceedings of the National Academy of Sciences reported that there could be as many as 40 billion habitable Earth-like planets in our own Milky Way galaxy alone. To say nothing of the incomprehensibly large number of planets likely scattered among the “billions and billions!” of other galaxies flung far into the distant reaches of deep space by the primordial Big Bang 13.7 billion years ago.
Now if only we would take better care of Mother Earth – the one “Earth-like planet” that we know for sure supports diverse and abundant life, including our own!
The exciting finding that Earth-like planets may not be so rare after all was based on analysis of data from NASA’s Kepler spacecraft. As the study’s authors reported:
A major question is whether planets suitable for biochemistry are common or rare in the universe. Small rocky planets with liquid water enjoy key ingredients for biology. We used the [NASA] Kepler telescope to survey 42,000 Sun-like stars for periodic dimmings that occur when a planet crosses in front of its host star. We found 603 planets, 10 of which are Earth size and orbit in the habitable zone, where conditions permit surface liquid water….The nearest such planet may be within 12 light-years.
Approximately one in five sun-like stars in the galaxy is estimated to have an Earth-sized planet orbiting in the so-called “Goldilocks” zone – that is, not too hot and not too cold. This is where surface temperatures should allow for water to occur as a liquid, an indispensable condition for life as we know it to appear and flourish.
“It seems that the universe produces plentiful real estate for life that somehow resembles life on Earth,” Mr. Petigura told The New York Times.
For those of us who shudder at the prospect that we may be “all alone in the universe” – who are comforted by the idea that somewhere out there in all that numbing, inaccessible vastness – life, and perhaps even intelligent life, might exist, these findings offer qualified hope.
The Search for Extra-Terrestrial Intelligence (SETI) is founded both on this hope and on the conviction that probability alone, given the sheer size of our galaxy – some 300 billion or more stars – argues that the appearance of life on Earth was not a unique event.
Yet SETI confronts the so-called Fermi paradox, the seeming contradiction between high theoretical estimates for the existence of extraterrestrial intelligence and the utter lack of any compelling evidence to date for it. Astronomer and author Paul Davies calls this “the eerie silence.”
CAPS Vice-President Ben Zuckerman, Ph.D., professor emeritus of physics and astronomy at UCLA, is no stranger to these issues. He dedicated his scientific career to studying the origin and evolution of planetary systems around various types of stars. He also co-edited a book called Extraterrestrials: Where Are They? in which experts weigh in on that Holy Grail of all scientific questions: “Is anybody out there?”
According to his UCLA web page, Prof. Zuckerman, “believes that if astronomy is to have a viable future then people must confront the declining environmental health of the world….if the U.S. and world environments become stressed too severely, then support of astronomy at anything like current levels may one day be regarded as an unaffordable luxury.”