Are We Alone?

Our sun is a star, one of hundreds of billions of stars.

In the past 16 years, scientists have founds more than 700 planets orbiting a few of the stars beyond our sun. These distant planets are often called exoplanets, short for extra-solar planet.

Just how many exoplanets are there in our Milky Way galaxy? Were researches just extremely lucky, looking where exoplanets exist? Or do they exist nearly everywhere?

Research published in the January 11, 2012 issue of Nature supports the idea that planets are as common as stars. Each of the 100 billion stars in our galaxy has on average at least one planet.

If life exists out there, it most likely exists on planets that are roughly like our earth. Not too big and neither too far from its sun (perpetual winter) or too close (blazing heat). Of all the planets, how many are roughly on the scale of earth? Half of them at least, maybe more.

Caption: This artist's cartoon view gives an impression of how common planets are around the stars in the Milky Way. The planets, their orbits and their host stars are all vastly magnified compared to their real separations. A six-year search that surveyed millions of stars using the microlensing technique concluded that planets around stars are the rule rather than the exception. The average number of planets per star is greater than one. Credit: ESO/M. Kornmesser

Arnaud Cassan of the Institut dʼAstrophysique de Paris and lead author of the paper explains: “We have searched for evidence for exoplanets in six years of microlensing observations. Remarkably, these data show that planets are more common than stars in our galaxy. We also found that lighter planets, such as super-Earths or cool Neptunes, must be more common than heavier ones,” Cassan said in a press release issued by the European Southern Observatory (ESO).

"We used to think that the Earth might be unique in our galaxy. But now it seems that there are literally billions of planets with masses similar to Earth orbiting stars in the Milky Way," according to Daniel Kubas, co-lead author of the paper.

If there are tens of billions of life-friendly planets just in our own galaxy, how likely is it that life exists out there somewhere? And if life exists, has intelligence evolved?

These are ancient religious and philosophical questions. The latest science certainly tilts the debate in favor of life. Sure, it’s possible that earth beat the odds: of the tens of billions of life-friendly planets, only ours has life.

Right now, there’s no evidence either way. All that science can tell us is that the planets are there, ready for the spark of life to get started.

So we are left to gaze at the night sky and to wonder as never before. For each star, there’s a planet. Is anyone out there looking back?

In Christian theology, one of the earliest statements about the Holy Spirit is that the Spirit is the “giver of life.” Hildegard of Bingen (Symponia) put it this way: “God our life is the life of all.” Or consider John Calvin, who says the Spirit is "everywhere diffused, sustains all things, causes them to grow, and quickens them in heaven and on earth."

To believe in God is to believe in the life-giving presence of God, not just here but everywhere. Thanks to this research, it turns out that the Spirit has many more planets on which to give life.

The article, "One or more bound planets per Milky Way star from microlensing observations", by A. Cassan et al., appears in the 12 January issue of the journal Nature.