Rare Earth

We are not alone. To believe contrary seems unscientific and unenlightened. Ever since Copernicus plucked our Earth from the centre of the universe and placed it in orbit around a rather ordinary star, humans too have been demoted from masters of the universe to just another civilization.

alien city

The idea that others are out there was popularized by astronomers Carl Sagan and Frank Drake. In 1974, they estimated that our Milky Way galaxy alone should contain a million civilizations. To think otherwise seemed egotistical.

It was against that backdrop that I read a contrary viewpoint by professors Peter Ward and Donald Brownlee in their book: Rare Earth, Why Complex Life is Uncommon in the Universe (2004).

They had no problem with the idea that life may exist elsewhere: after all, bacteria have been found on Earth in the most hostile places. But anything beyond the most basic was unlikely. “In other planetary systems, primitive life might flourish but never advance to the point where forests and flying animals even get a serious chance to evolve.”

There are many arguments for a rare Earth but here are three: location, location, location. First, the right distance from a star. Complex life requires what Carl Sagan called a “habitable zone.” Otherwise, no liquid water and we cook or freeze.

Habitable planets have to be located in the right part of galaxies. Not too close to centre where black holes gobble up solar systems and things are chaotic. Not near the edge where stars don’t have enough metals.

Life needs the right kind of galaxy. Not globular clusters where stars are too hot. Not elliptical or small galaxies that are metal-poor.

Sagan notwithstanding, things seemed gloomy for the prospect of millions of civilizations until the Kepler satellite discovered more than a thousand of planets. Some even appeared to be within the habitable zone.

But on closer examination, Earth still seems as exceptional as Ward and Brownlee suggested more than a decade ago. A study by astrophysicists  Konstantin Batygin and Greg Laughlin takes a closer look at these newly discovered planets.

Dr. Laughlin told the CBC science program Quirks and Quarks: “This flood of information made our solar system stand out like a sore thumb.” What makes our solar system unique is the lack of big planets close to the sun. The systems that Kepler discovered have gas giants near the star, more like Neptune than like Earth.

Also unique in our solar system is the position of Jupiter which has more mass than all the other planets combined. Laughlin and Batygin confirmed an earlier idea that Jupiter moved close to the sun in the early development of our solar system and gobbled up all the planet-making material. No wonder Jupiter is so fat.

In one fell swoop, Jupiter cleaned up the buffet and then joined in a dance with that other giant, Saturn, to move back from where it came. This dance is called a resonance in which Jupiter rotates three times for every two of Saturn.

The notion that we are alone is hard to take but the dream of other civilizations is getting dim.


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