Focus Off Ourselves, on Rest of Universe

Our perception of our place in the universe has changed throughout history.

At first, we were at the center of everything, and the universe revolved around us.

The works of Copernicus, Galileo, Kepler, Newton and others dislodged that notion. It became understood that the planets, including us, orbit the sun. And not in perfect circles, but in elliptical orbits, whose motions could be described with mathematics.

In the 20th century, we came to better understand the nature of the universe. Even the sun was not at the center. The planets were realized to be other worlds different than our own. Stars are born, live and die. And our Milky Way Galaxy is not the whole of the cosmos.

Today, science has painted for us a remarkable picture. After 1,500 years of being at the center of everything, we have been demoted.

We now know that we are one species among millions that evolved on one world, orbiting one star among billions, in one galaxy among billions.

How very humbling.

As our knowledge improved, it seemed natural to wonder if these other stars had planets of their own. Indeed, the models of stellar evolution suggest that planets are a natural consequence of star formation. The task then became to find them.

And we have.

Since 1995, more than 127 planets orbiting other stars – extrasolar planets – have been discovered around 98 other stars. This confirms that our own solar system is not unique, and that we are just one neighborhood in a vast city of stars.

The methods used by scientists to locate these planets are ingenious. When two bodies orbit one another, neither is at the center of the system. They both orbit a common center of mass.

Consider, for example, the Earth orbiting the sun. The mass of the Earth pulls the sun off center by approximately 280 miles, about the length of Tennessee.

The nearest star, Proxima Centauri, is 4.2 light years away, or 25 trillion miles. From that distance, this wobble of the sun would be the same as looking at a coin on edge from 46,000 miles away.

While this is a small amount of movement, we can detect this stellar wobble. Until recently, the planets we have found around other stars were massive – about the size of Jupiter.

But our technology and methods are growing.

On Aug. 31, NASA announced the discovery of a new class of extrasolar planets. Two worlds were found around other stars that are only 10 to 20 times the mass of Earth and are already being described as “Neptune-like.” These are far smaller than any previously detected. It is not yet known if they are gaseous, like Jupiter and Neptune, or actually made of rock and metal, like Earth.

One of these planets orbits a star called Gliese 436, 30 light years away in the constellation Leo. Gliese 436 has a mass only 40 percent that of our sun.

The second planet actually joins three other previously discovered extrasolar planets around the star 55 Cancri, 41 light years away in the constellation Cancer. 55 Cancri is just a little less massive than the sun.

Because Gliese 436 and 55 Cancri are not very massive stars, they are more susceptible to be pulled off center by smaller planets orbiting them.

First, we could only study the stars. Then, we learned how to find large, Jupiter-like worlds around other stars. Now, we can find extrasolar planets the size of Neptune.

It is only a matter of time before we find another Earth.

And then we will firmly know that we are not alone.

Thomas R. Webber is director of the Heritage Planetarium in Blount County. If you have a question about an astronomical happening, email him at skyguy@blountk12.org.