Well, Earth-like planets to be precise. What does that mean, you ask? You see, Earth is a very SPECIAL planet. Special in the sense that it is the only planet that we (currently) know of that can support life.
How does Earth support life?
For starters, Earth is right DISTANCE from our Sun, in what some call the Goldilocks Zone (also known as the habitable zone). It is the region where water can exist in a liquid form on the surface of a planet. Too much closer and the heat from the sun would boil away all the water. Too far, and there isn’t enough heat causing any water on the planet to freeze.
Earth is also a TERRESTRIAL planet, meaning that part of the surface is solid, i.e. made up of rocks and dirt. The Earth is also large enough to have a GRAVITY that can have an atmosphere, you know, the air we breathe. Without enough mass, the gravity would be too low to prevent the air from escaping out into space. You can read more about this in my book. 😉
Believe it or not, those are the pretty much all the things that are needed for a planet to support life. What about OXYGEN, you ask? Oxygen that we breathe is created by plants, which are a form of life. You would think, with these meager requirements, there are probably HUNDREDS, if not thousands, of planets that can support life.
The thing is, detecting other Earth-like planets is not an easy thing to do. Stars are really far away, and planet that may exist around those stars tend to be very TINY compared to the star they orbit. Our own Sun contains more that 99% of all the mass in our solar system. And our, habitable Earth is quite small compared to giants like Jupiter and Saturn.
Kepler, the planet hunter.
As you can imagine, looking for other Earth-like planets is not an easy task. However, a space mission launched in March of 2009 aims to do just that. Kepler, named after the astronomer, Johannes Kepler carries very POWERFUL cameras to catch a planet transiting its parent star. A transit is when the planet that we are looking is in between us and its parent star as the planet goes around the star. When the planet is between us and its star, the brightness of that star as seen by us is lower than when the planet is behind star. The animation below explains it better than I can write it.
Look at the sky on a clear night. What is the largest star you see? Imagine looking for a planet in front of that star. A tiny Earth-like planet around a star that already looks only like a dot from where we are. That is what Kepler is trying to do. At a lecture given by a Kepler mission scientist that I attended, she said that they expected to find about a 100 Earth-like planets in the tiny patch of the sky it will look at. Whether those planets will have ALIENS will be another matter.
- Goldilocks and The Three Bears (in text form).
- Stars and habitable planets.
- Kepler mission’s education and public outreach.