Week 8: Earths (and Life) Away From Earth

This week in class we have been talking about how to observe exoplanets. We've learned that in general, larger planets that are closer to their stars, like hot Jupiters, are the easiest to observe. However, for me at least, these aren't the planets that are the most interesting. I'm much more interested in the planets that would be able to support life--especially life as we know it. This is a job that the Kepler Space Telescope has been working on since 2009, and it has found some pretty interesting candidates.

One of the most promising Earth-like planets that Kepler has found is Kepler-186f. This planet, which was discovered in 2014, has a radius about 10-20% larger than that of the Earth. Furthermore, Kepler-186f orbits within a region around its parent star known as the habitable zone. This band is defined as the region in which liquid water can exist, although this definition can be somewhat flexible depending on the mass and atmospheric conditions of the planets in question. Fortunately, Kepler-186f lies in the "conservative" habitable zone, outside of which only larger-than-Earth planets could have liquid water.

While it can be difficult to determine the planet's composition, the planet's small size indicates that it is likely not a gaseous planet. Instead, scientists predict that it is a rocky planet, like our own. Assuming similar composition to Earth's, Kepler-186f would have a mass of about 44% greater than the Earth's (although estimates based on compositions with more water or iron range from a third to about 4 times Earth's mass). However, Kepler-186f is close to 500 lightyears away, which will make investigating its surface for life very difficult until our technology improves.

Searching for life by looking for Earth-like planets that lie in their stars' habitable zones has been criticized by some scientists for focusing too closely on the idea that extraterrestrial life must be carbon-based and need liquid water (an idea which has the awesome name "carbon chauvinism"). For example, silicon, which, like carbon, forms 4 bonds, has been proposed as an alternative basis for biochemical systems, especially for colder environments--which I think this is a really cool idea. However, the only examples of life we know of are all carbon-based, so I think until both observational astronomy and biochemistry have advanced quite a bit, we should stick to what we know.



Sources
http://www.space.com/30172-six-most-earth-like-alien-planets.html
https://en.wikipedia.org/wiki/Kepler-186f
https://en.wikipedia.org/wiki/Circumstellar_habitable_zone
http://www.nasa.gov/ames/kepler/nasas-kepler-discovers-first-earth-size-planet-in-the-habitable-zone-of-another-star
https://en.wikipedia.org/wiki/Carbon_chauvinism
http://topinfopost.com/wp-content/uploads/2015/02/new_earthh.jpg