Our sun is located in a spiral-shaped collection of stars known as the Milky Way. You’ve undoubtedly heard of the Milky Way, but you may not realize that it is our home galaxy. Day or night, summer or winter, everything you see in the sky is part of the Milky Way, including the sun, the moon, the stars, the planets and the occasional meteor. Everything. Astronomers estimate that the Milky Way contains up to 400 billion stars. It is difficult to imagine 400 billion. To visualize numbers like this, it helps to write all the zeroes. That’s 400,000,000,000. Almost lost within this enormous collection of stars, our sun is a yellow star among red giants, blue giants, and white dwarfs. In the end, our sun is just another star in the Milky Way, one in 400,000,000,000 to be exact.
Wouldn’t it be interesting if some of the other stars in our galaxy had planets like the earth? After all, why should our sun, with its collection of planets that we call a solar system, be the only star with planets in orbit around it? When you think about, it seems kind of unlikely that only one of the 400,000,000,000 stars in the Milky Way would have planets, doesn’t it? The trouble is, how would we know if a distant star has a “solar system,” or a collection of planets orbiting it? The nearest star to us (besides our own sun) is located 25 trillion miles away (if you want to see all the zeroes in that number, it’s 25,000,000,000,000). That’s an incomprehensible distance! It takes a powerful telescope just to see the planets in our own solar system…how could we possibly see a planet that orbits a star 25 trillion miles away? And as we know from our own solar system, planets are not very bright, especially compared to their shining host star. So, looking for a distant planet is a little like spotting the taillights of a single car in New York City while you are looking down on the earth from a spaceship. Not easy indeed.
But astronomers are a clever group, and starting in the 1990s, they began to use some very creative measurement techniques to infer the presence of planets around distant stars. It turns out that an orbiting planet affects the brightness and position of its host star in very small, but measurable ways. As a planet orbits, the position of the host star wobbles slightly, or dims faintly, in regular and repeatable patterns. Based on these patterns, astronomers developed indirect evidence for the presence of planets in orbit around a handful of distant stars. Astronomers call these planets “exoplanets” because they are external to our solar system.
The first exoplanet was discovered in 1992. Twenty years later, the list of known exoplanets had grown to several hundred. Earlier this week, astronomers announced the discovery of more than a thousand new exoplanets, almost doubling the number of known exoplanets. These latest discoveries were made possible by NASA’s Kepler telescope, which is an observatory that orbits the earth in a fashion similar to the Hubble space telescope. Except Kepler is specifically designed to detect the presence of exoplanets.
It is amazing how much we already know about distant exoplanets. For example, in most cases, astronomers can determine the mass of an exoplanet, the orbital frequency (i.e., the length of “a year”) of the exoplanet, and the distance between the exoplanet and the host star. Some of the new exoplanets are rocky planets like our earth and also about the same distance from their host star as our earth is from our sun. The ramifications are mindboggling to me.
It is not possible to know exactly how many of the 400,000,000,000 stars in our galaxy have planets, but it is now clear that planets, like those in our very own solar system, are commonplace in the Milky Way. It is also not possible at this stage to know if any of the known exoplanets have an atmosphere like our earth, which contains water and oxygen and can support carbon-based life as we know it. But future observatories planned by NASA will be able to explore these possibilities. That gives me goose bumps!
If the history of the cosmos has taught us anything, it is that our planet and our sun are nothing special in the vastness of space. The earth is not the center of the solar system, as we once believed. And the sun is not the center of the universe, as we also once believed. Now, we know that other planets are commonplace as well!
You can tell that this is all amazing to me, so I’ve chosen to share a picture of the Milky Way from the perspective of a very special planet to me: the earth. Specifically, from the perspective of a place called Aguereberry Point in the western region of Death Valley National Park. Aguereberry Point is a fantastic place to see the sunrise. As you can see in this image, it is also a fantastic place to see the Milky Way as well. As you look at this image, which is really a pathetic representation of our galaxy that only resolves a few hundred stars, try to wrap your mind around the 400,000,000,000 stars in the Milky Way. Try to wrap your mind around the possible exoplanets out there based on these latest findings from the Kepler telescope. Finally, try to wrap your mind around the possible ramifications of these findings on our understanding of our planet, our solar system, and our universe. What a cool time to be a human being!
I hope you want to learn more about exoplanets and the Kepler findings. Check out this article on space.com: http://www.space.com/32850-nasa-kepler-telescope-finds-1284…