This week NatGeo posted an interesting article about a recently published study estimating the number of Earth-sized planets in our galaxy. Researchers used data provided by the Kepler Space Telescope, which is currently peering at a group of 156,000 stars.
The thinking goes that if these stars show a regular pattern of dimming and brightening, it may indicate a planet is crossing our field of view as it orbits its parent star. An analog might be how moths flutter around your porch light. As they pass in front of the lightbulb, they block a small fraction of light. If these moths are big enough, we might notice the brightness of light fluctuating.
That’s the same idea here, except Kepler is looking for the tiniest of variations. From there it comes down to mathematics. How much light the transiting planet blocks can give an indication of the planet’s size and mass. How often it crosses the star can tell us how long its orbit is. The brightess and color of the star can tell us if the planet is inside the star’s “habitable zone”, the area around a star where water can exist in liquid form.
Of course, as with all such studies, there is some discussion on whether it is actually right or not. The science of detecting planets is still in its infancy, and Kepler is the first dedicated research tool. This study is one of the first with only a limited amount of data, still it estimates there may be as many as 2 billion Earth-sized planets in our galaxy. Others say that is way too conservative a figure.
The article goes on to touch on the next steps, which would help us discover if these Earth-sized planets are Earth-like. Not only can they support liquid water and an atmosphere with oxygen, but do they? The technology to answer such a question doesn’t yet exist, but studies such as this one help us to build the tools that will answer those questions.
Question: How many years do you think it will take to be able to determine if a planet orbiting another star has liquid water? How many years to learn if it has chlorophyl or other indicators of life?