What if we dropped the “terrestrial” from “extraterrestrial”? Scientists recently explored the intriguing possibility that alien life may not need a planet to support itself.

At first glance, planets seem like the ideal locations to find life. After all, the only known place life is known to exist is Earth’s surface. And Earth is pretty nice. Our planet has a deep gravitational well that keeps everything in place and a thick atmosphere that keeps surface temperatures in the right ranges to maintain liquid water. We have an abundance of elements like carbon and oxygen to form the building blocks of biological organisms. And we have plenty of sunlight beaming at us, providing an essentially limitless source of free energy.

It’s from this basic setup that we organize our searches for life elsewhere in the universe. Sure, there might be exotic environments or crazy chemistries involved, but we still assume that life exists on planets because planets are so naturally suited to life as we know it.

In a recent pre-paper accepted for publication in the journal Astrobiology, researchers challenge this basic assumption by asking if it’s possible to construct an environment that allows life to thrive without a planet.

This idea isn’t as crazy as it sounds. In fact, we already have an example of creatures living in space without a planet: the astronauts aboard the International Space Station. Those astronauts require tremendous amounts of Earth-based resources to be constantly shuttled to them, but humans are incredibly complex creatures.

Perhaps simpler organisms could manage it on their own. At least one known organism, the tiny water-dwelling tardigrades, are able to survive in the vacuum of space.

Any community of organisms in space needs to tackle several challenges. First, it needs to maintain an interior pressure against the vacuum of space. So a space-based colony would need to form a membrane or shell. Thankfully, this isn’t that big of a deal; it’s the same pressure difference as that between the surface of water and a depth of about 30 feet. Many organisms, both microscopic and macroscopic, can handle these differences with ease.

The next challenge is to maintain a warm enough temperature for liquid water. Earth achieves this through the atmosphere’s greenhouse effect, which won’t be an option for a smaller biological space colony. The authors point to existing organisms, like the Saharan silver ant (Cataglyphis bombycina), that can regulate their internal temperatures by varying which wavelengths of light they absorb and which they reflect — in essence, creating a greenhouse effect without an atmosphere. So the outer membrane of a free-floating colony of organisms would have to achieve the same selective abilities.