The Search for Earth

N = the number of civilizations in our galaxy with which communication might be possible;

R_* = the average rate of star formation per year in our galaxy

f_p = the fraction of those stars that have planets

n_e = the average number of planets that can potentially support life per star that has planets

f_ℓ = the fraction of the above that actually go on to develop life at some point

f_i = the fraction of the above that actually go on to develop intelligent life

f_c = the fraction of civilizations that develop a technology that releases detectable signs of their existence into space

L = the length of time for which such civilizations release detectable signals into space

What is this? This is Drake's Equation. What does it tell us? It tells us the chances of finding intelligent life elswhere in the galaxy. 

Humans have been infatuated with the idea of life elswhere in the universe for decades. From movies to video games to comics, our culture is obsessed with "little green men from Mars". The greatest TV series ever produced, Star Trek, is based entirely on the entreaction of various species in the galaxy. The thought of someone else being out there is compelling, and according to the latest research from NASA, maybe not as impossible as once was thought. 

Backtrack to my posts about space colonization. What does life as we know it need to survive? 

• Oxygen
• Water
• Food
• Proper temperature
• Proper ecosystem

Earth, obviously, provides all that we need for this. But what about other planets? 

NASA is studying planets orbitting stars light years away from Earth to determine if they rest inside the "habitable zone". The habitable zone is where water is found in the liquid state. If water is a liquid and not a solid or a gas, then we know that a nitrogen-oxygen atmosphere will be a gas, not a solid or liquid, because the temperature range where water remains a liquid is entirely inside the temperature range for the atmosphere to be gas. 

The habitable zone has a wider range than is normally expected. The habitable zone can be from ver close to very far away from the star, depending on the size and energy output of the star. This means that a very low energy output star's habitable zone is much closer to it than the habitable zone of a high energy star. 

We can determine how far away a planet is from it's star with a lot of very complicated math which I won't go into now. Basically though, we can determine how close it is by how much a star's light "flickers". Toss a ball past a lightbulb and watch how it blocks the light for a minute to see what I'm talking about.  

Once we find a planet in the habitable zone, the next step is to determine the surface temperature of the planet. NASA's orbitting infrared telescopes are able to measure surface temperature of far away planets. Once we know the surface temperature, we know if it is possible for liquid water to exist on the planet. If so, then there may be the presence of life on the planet. 

If we do find life, it will probably be only in the bacterial form, but life of any sort will still be a step closer to understanding the secrets of the galaxy. 

Go to www.planethunters.org to learn more about planet hunting. You can even sign up to hunt planets yourself!