New Delhi, India

Astronomers have been looking for signs of life in other galaxies and planets. But what if life doesn't need a planet to thrive in the universe? Scientists have come up with a fascinating theory that suggests life might simply be floating in space while we look at planets to locate it.

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A recent pre-paper accepted for publication in the journal Astrobiology suggests that life can exist anywhere in the universe simply by itself if the right environment exists that allows life to thrive without a planet.

The tiny water-dwelling tardigrades are an example of an organism that can survive in the vacuum of space. The paper says that any community of organisms needs a set of conditions to thrive. 

It needs to maintain an interior pressure against the vacuum of space, like a membrane or shell. This should not be a problem since it is the same pressure difference as that between the surface of water and a depth of about 30 feet 

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For liquid water to exist, a warm enough temperature is the next requirement. On Earth, the atmosphere's greenhouse effect achieves this, but for a smaller biological space colony this might not be possible.

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The researchers cite the Saharan silver ant that can regulate its internal temperatures by varying which wavelengths of light it absorbs and which it reflects. This way they are creating a greenhouse effect without an atmosphere. A free-floating colony of organisms would also need to emulate this form.

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They would also need to overcome the loss of lightweight elements, something the planets maintain through the sheer force of gravity. Even in the best-case scenario, a colony would lose lightweight elements over the course of tens of thousands of years. How it manages to replenish itself will also be a big factor.

Free-floating life would depend on asteroids for resources

The colony also need to be within the habitable zone of its star to get sunlight. For things like carbon or oxygen, it would need to depend on something like an asteroid that could bring the elements to it and move to a closed-loop recycling system among its various components to sustain itself over the long term.

The paper posits that if all these factors can exist together, a free-floating colony of life is possible in space. It could be 330 feet across, and sit within a thin, hard, transparent shell that would stabilise its interior water to the right pressure and temperature and to create and maintain a greenhouse effect.