Planets, Planets 

This composite of the Large Magellanic Cloud (LMC), a small satellite galaxy of the Milky Way located about 160,000 light years from Earth. NASA

Tonight, after reading this article, you will never see the starry night sky in the same way again. Gazing at the splendor of the Milky Way galaxy, you will ask yourself, “Is anyone looking back?”

It’s official: in our own celestial backyard, our galaxy holds 100 billion planets, a number beyond human comprehension. About half the stars in our galaxy have planets going around them; however, most of them are huge and unable to support life as we know it. But many—about 17 billion—are roughly the size of Earth. For the first time in his­tory, we now have a “census” of the galaxy extrapolating from a sample: about one in six stars has Earth-size planets revolving around them.

These are the astounding results from the Kepler satellite, announced this week at the American Astronomical Society Meeting in Long Beach, Calif. The Kepler satellite, launched in 2009, can detect tiny Earth-like planets because they occasionally pass in front of their mother star, causing a slight dimming of starlight. Kepler has now identified 2,740 potential planets orbiting 2,036 stars, in this way.

This raises the eternal question: is anyone out there? Back in 1600, the former monk Giordano Bruno was burned alive in the streets of Rome for claiming that life can thrive on alien planets. Fortunately, we don’t burn astronomers at the stake anymore. But it does raise interesting theological and philosophical questions about our place in the universe. Arthur C. Clarke once said, “Either intelligent life exists in space or it doesn’t. Either thought is frightening.”

But don’t worry. The aliens aren’t going to land on the White House lawn anytime soon. The distances between the stars are huge. It would take 70,000 years for a Saturn rocket to reach even the nearby stars.

To be sure, most of these planets are probably dead, incapable of supporting life as we know it. And of the Earth-like planets, many may harbor only primitive, microbial life. After all, life has existed on Earth for about 3.5 billion years, but only in the past 200,000 years has intelligent life (us) risen from the swamp. But perhaps a handful of these planets harbor intelligent civilizations. So this leads us to the final question: why don’t they visit us? Or maybe they have?

Scores of answers have been given (mainly by Hollywood screenwriters). My own feeling is this: if you walk down a country road, and encounter an anthill, do you bend down to the ants and say, “I bring you trinkets. I bring you beads. I promise you an Age of Aquarius. Take me to your leader?” Probably not­—you’d just walk on by.

Personally, I think that the aliens, if they exist, will be peaceful. After all, as Kepler has shown, there are plenty of other planets to plunder for resources if they felt like it. So relax, they come in peace.