Galactic Habitable Zone

This post is sort of an addendum to the two Kepler posts made last week, here and here. As you can probably tell, I am pretty much obsessed with Kepler information right now. The two things I wanted to add were (1) the concept of a galactic habitable zone and (2) a couple of Kepler Objects of Interest, or KOIs. You'll probably be hearing about a few KOIs in the future, as more and more data gets sifted through.

So first, the galactic habitable zones. When I did the calculations for the Kepler posts for the spacing out of possible civilizations, I assumed that any civilization would be roughly about as far from the galactic center as our own solar system. There is actually a good reason for this.

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Not all locations in the Milky Way seem to be fit for life. Our bodies, the Earth, our entire solar system is made up of a complex chemistry of elements. In astronomy, any elements higher then hydrogen and helium are collectively called 'metal,' even chemically non-metallic elements like oxygen, carbon, and chlorine. From now on, when I mention metals, this is what I'm referring to. Metals make up a small part of things, about 2% of the Sun and the Milky Way, but are hugely important for planet formation and life.

To create metal, you need the energy for nucleosynthesis (think of it a bit like alchemy, creating new atomic nuclei from existing particles). For the kind of metals we're looking for, you need supernova. Our solar system was created out the debris created from supernova. In essence, as Carl Sagan says, you are made up of star stuff. But the activity that creates supernova that can seed stellar nurseries only occurs in certain areas of the galaxy. This occurs in denser regions, where supernova occur close to the stellar nurseries. Once you get further out from the galactic center, near the edge of the galaxy, there isn't much star birth going on and supernova are more spread out. It is a metal poor region, not conducive of life. Therefore, forming the outer edge of the galactic habitable zone.

Now that we have the outer edge defined, we need to define the inner edge. The inner edge is defined by two concepts. The easiest is by radiation, life as we know it has a limit to how much radiation it can withstand. So, looking inward on the Milky Way, the denser it gets, the more radioactive it is. However, knowing some extremophiles thrive in radioactivity, there might be life, but it might not be a civilization. The other concept is with this denseness, stars interact more often. This would cause disturbances to planets, their stability would be low. Life, from our experience, seems to need long stable periods to reach civilization, and planets flying all about are probably not going to be helpful for that. So between these two spots we have out galactic habitable zone, a zone where our solar system appears to be smack dab in the middle of. Lucky us.

Moving onto the KOIs now. The first is KOI 730, which appears to be two planets sharing the same orbit. They are more or less permanently separated by 60 degrees, inside each others Lagrange points. Lagrange points being gravitationally stable regions between a planet an its star, there is one 60 degrees in front of and behind a planets orbital path, along with others. This is an incredibly rare find, and exciting because it lends support to the theory that Earth once shared its orbit with another Mars-sized planet, eventually colliding (probably through Jupiter's gravitational influence) and creating the Moon. The linked article sums it up well.

The other object is KOI 326.01, which is being called the cream of the Kepler crop. It is the closest Earth analog found so far. It's slightly smaller then Earth, within the star's habitable zone, and about 100 light years away, making it 'fairly close' in astronomical terms. This might be where our neighbors are, but it might take 100 years to contact them, and another 100 to hear back from them. So its still an immense distance, but closer then the one I had proposed before for possible civilizations. Heck, it might just turn out to be a Venus or Mars. It will definitely be good to follow the development on this object. Also, it should be mentioned that KOIs are not yet confirmed Kepler finds, they are objects of interest in the data, confirmation is pending. But that said 90% of the Kepler data is thought to be real planets, not false positives.

Hope you enjoyed the update!

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