Does extraterrestrial life need a planet to survive? Scientists propose an intriguing possibility

What if we removed the “terrestrial” from the word “extraterrestrial”? Scientists have recently explored the intriguing possibility that extraterrestrial life does not need a planet to support itself.

At first glance, planets seem like ideal places to find life. After all, the only place where life is known is the surface of the Earth. And Earth it’s quite nice. Our planet has a deep gravitational well that holds everything in place and a thick atmosphere which keeps surface temperatures in the right ranges to keep water liquid. We have an abundance of elements like carbon and oxygen that are the building blocks of biological organisms. And we benefit from lots of sunlight, providing an essentially unlimited source of free energy.

It is from this basic configuration that we organize our search for life elsewhere in the universe. Sure, there may be exotic environments or crazy chemistries involved, but we continue to assume that life exists on planets because planets are so naturally suited to life as we know it.

In a recent pre-article accepted for publication in Astrobiology magazineResearchers are challenging this basic assumption by asking whether it is possible to build an environment for life to thrive without a planet.

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This idea is not as crazy as it seems. In fact, we already have one example of creatures living in space without a planet: the astronauts aboard the International Space Station. These astronauts require enormous amounts of Earth’s resources to be constantly delivered to them, but humans are incredibly complex creatures.

Perhaps simpler organisms could handle it themselves. At least one known organism, the tiny aquatic tardigrades, is capable of surviving in the vacuum of space.

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Any community of organisms in space faces several challenges. First, it must maintain inner pressure against the vacuum of space. So, a space colony should form a membrane or shell. Fortunately, it’s not that bad; this is the same pressure difference as that between the water surface and a depth of about 30 feet (10 meters). Many organisms, both microscopic and macroscopic, can easily handle these differences.

The next challenge is maintaining a warm enough temperature for the liquid water. Earth achieves this through the greenhouse effect of the atmosphere, which will not be an option for a smaller biological space colony. The authors point to existing organisms, such as the Sahara silver ant (Cataglyphis bombycina), which can regulate their internal temperature by varying the wavelengths of light they absorb and those they reflect – essentially creating a greenhouse effect without an atmosphere. Thus, the outer membrane of a colony of free-floating organisms should acquire the same selective capabilities.

They would then have to overcome the loss of light elements. Planets maintain their elements through the simple force of gravitybut a biological colony would struggle with this. Even optimistically, a colony would lose light elements over tens of thousands of years and would therefore have to find ways to replenish itself.

Finally, the biological colony would need to be positioned in the habitable zone of its star, to access maximum sunlight. As for other resources, like carbon or oxygen, the colony should start with a steady supply, like an asteroid, and then move to a closed-loop recycling system between its various components to sustain itself over the long term.

Putting it all together, the researchers paint a picture of an organism, or a colony of organisms, floating freely in space. This structure could measure up to 330 feet (100 m) in diameter and would be contained by a thin, hard, transparent shell. This shell would stabilize its internal water at the right pressure and temperature and allow it to maintain a greenhouse effect.

Although such organisms may or may not exist in the universe, the research has important implications for future human activities in space. While we currently build habitats with metal and supply our stations with air, food and water transported from Earth, future habitats could use bioengineered materials to create self-sustaining ecosystems.

Originally published on Espace.com.

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