The Search For Extraterrestrial Life
Scientists have been searching for extraterrestrial life for decades. Moreover, speculation about alien life in other planets is at least more than 100 years old. But only in the last few decades has there been a concerted effort to understand the conditions that might create and support alien life. This is more than intelligent life; rather it is understanding the conditions for any form of life to exist in distant planets.
The Goldilocks Zone
For any life to manifest itself in a planet, several conditions must be present. First, the planet must have mass and not be a gas giant like Jupiter or Saturn. The mass can’t be so overwhelming that it crushes the molecules of life and they are unable to grow.
Secondly, the planet must be in the “habitable zone” near a star, otherwise known as the Goldilocks zone. It cannot be too close or too far away from the star. If it is too close, the heat will prevent the formation of life. If it is too far away, the cold will also prevent the formation of life.
Third, the planet must have an atmosphere with oxygen and water. At this time, scientists can only speculate about the formation of life if these chemicals are present. Those chemicals currently define what life is and how to create it. So exoplanets must have those elements present if the bare conditions exist to create life.
The Kepler Mission
Two years ago, NASA launched the Kepler Satellite mission project, which had one scientific goal: identify stars and planets surrounding those stars that could be in the Goldilocks zone.
By February 2011, NASA had identified 1,235 with 997 host stars. And to date, 677 planets have met the criteria to qualify as an exoplanet.
Super Earth
With these entire planet candidate’s list of alien planets, there includes 16 super Earths, which are potentially rocky worlds that are more massive than our planet. A Super Earth is a planet measured by its mass slated to be between one and 10 times that of Earth. This classification only refers to the mass of the planet, not about the surface conditions or habitability.
So, have any Super Earth’s been found? Yes. In fact, in the first Super Earth discovery, two exoplanets with masses four times that of Earth were orbiting a pulsar called PSR B1257+12. Pulsars, however, expel too much radiation to be considered viable sources for life. Instead, scientists look for main sequence stars, one that is on order with our Sun. The first Super Earth around a main sequence star was discovered in 2005. It has an estimated mass of 7.5 Earth masses and orbits the star Gliese 876. The Super Earth is called Gliese 876 d. Dozens more Super Earths have since been discovered with masses as low as 1.9 Earth masses.
But recently, one Super Earth called HD 85512 b has generated a lot of buzz because it orbits at the edge of its star’s habitable zone, suggesting conditions could be ripe to support life.
With all of this activity going on investigating Super Earths, astronomers can only hope it will be a matter of when not if they will discover a truly viable exoplanet that harbors life.