What Makes Earth So Perfect for Life?

What makes a world such as ours able to host life?

The closest star system to our own made headlines yesterday with the announcement that it hosts a planet about the mass of Earth — a tantalizing discovery so close, astronomically speaking, to us. While the newfound planet may be Earth-sized, researchers say it is almost certainly barren. Astronomers detected the alien world around the sunlike star Alpha Centauri B, which is a member of a three-star system only 4.3 light-years away from our solar system. This planet, known as Alpha Centauri Bb,is about as massive as Earth, but its hot surface may be covered with molten rock — its orbit takes it about 25 times closer to its star than Earth is from the sun. "We're pretty sure there's no chance of life on this planet," said MIT planetary scientist Sara Seager. So what makes a world such as ours able to host life? Why is Earth so special? There are a few key ingredients that scientists often agree are needed for life to exist — but much debate remains as to what limits there actually might be on life. Even Earth hosts some strange creatures that live in extreme environments.

"First, you'd need some kind of liquid, any place where molecules can go react," Seager told OurAmazingPlanet. In such a soup, the ingredients for life as we know it, such as DNA and proteins, can swim around and interact with each other to carry out the reactions needed for life to happen. The most common contender brought up for this solvent is the one life uses on Earth: water. Water is an excellent solvent, capable of dissolving many substances. Second, life needs energy. Without energy, virtually nothing would happen. The most obvious source of energy is a planet or moon's host star, as is the case on Earth, where sunlight drives photosynthesis in plants. The nutrients created by photosynthesis in turn are what the bulk of life on Earth directly or indirectly relies on for fuel. Other factors researchers have trotted out for why life succeeded on Earth include how little variation there is in our sun's radiation compared with more volatile stars, or how our planet has a magnetic field that protects us from any storms of charged particles from the sun. Earth remains the only known planet to host life, due to a unique combination of factors.


However, continued monitoring of alien worlds might one day change that, by finding other planets that share these attributes or by discovering other ways that life has found to blossom in the universe.


Kemo D. 7

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