SUMMERS: NASA’s Center For Life Detection Is On The Hunt For Life In The Universe

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Knowing if something is alive or not is easy. Right? Barking dogs and flying birds are alive. Rocks are not. Turtles and polar bears are alive. Water is not. And so on. The difficulty of knowing what is, and is not, alive comes about when we consider things that are close to the boundary between the two domains. For instance, a mold is alive, but it takes some patience to see it grow. Bacteria are alive, but are so small to be invisible to the unaided eye. Viruses have characteristics of both domains.

We learn in high school that living things share some common characteristics. For example, living things metabolize materials from their environment to get energy for growth and reproduction. But fire metabolizes, and it’s certainly not alive. Crystals grow and reproduce, but are not alive. On the other hand, mules (the offspring between a horse and donkey) are clearly alive, but cannot reproduce.

Most life on Earth, whether measured by mass or numbers, is the bacteria. And many bacteria live in extreme environments, such as deep underground or in the deep ocean. They are called extremophiles — they live in extreme environments, at least from the perspective of humans. Many times they live in environments that would kill us.

One of NASA’s goals in astronomy is to understand the long and rich story of life in the universe. An important aspect of that goal is to search for life on other worlds. But how do you go about detecting life elsewhere if it is extreme life, it is at or near the boundary between the domains of living and non-living things, that could be vastly different from life on Earth, and that is very, very far away. It is an incredibly difficult task.

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