The Search for Another Earth

Photo Source:  projectarchive.net

Are we alone in the universe?  This fundamental question has been asked since mankind first looked up into the night sky.  With the successful launch of the Kepler space telescope, astronomers are one step closer to finding an answer.  The search for life throughout the cosmos begins with the search for planets.  Preferably for planets similar in composition to a planet that we know can harbor life, like Earth. 

The search for another Earth is simply the search for a planet that can sustain liquid water.  Liquid water is the critical substance that allows the chemical reactions to take place that can eventually lead to life.  To sustain liquid water a planet must be in what astronomers deem the habitable zone –  the zone in which a rocky planet is not to hot (like Venus) and not to cold (like Mars).  Astronomers have theorized on other factors that an Earth-like planet must contain including:

• The size must be similar to Earth.  This would allow the planet to hold on to its atmosphere.
• The planet must be in a peaceful spot in its galaxy, away from dangers like black holes and deadly neutron stars.
• The planet’s solar system must contain a huge gas giant planet like Jupiter.  This Jupiter-like planet would gravitational protect the Earth-like planet from asteroids and mass extinctions. 
• The planet must have plate tectonics. This would keep the planet cool, recycle its elements and bring heavy metals to the surface.

Currently astronomers have found over 340 exoplanets, which are planets found in other solar systems.  Most of these planets were found by the radial velocity method.  In this method astronomers study the wobble of a star, or the gravitational pull of a planet around its host star.  From the size and frequency of the wobble, astronomers can calculate the number, size and temperature of the planet or planets orbiting the star.  Nearly all the exoplanets found have been gas giants 4 to 10 times larger than Jupiter that orbit their host star very frequently (some in as few as 4 days). 

The technological advances of Kepler will allow astronomers to find planets differently using the transit method.  Cameras onboard Kepler will take constant pictures of stars similar to our sun for 3.5 years and observe the slight dimming of a star when a planet crosses the light path between a star and the telescope.  This method should yield results that help astronomers find smaller planets similar to the size of Earth in the habitable zones of distant solar systems.