Biologists who study extremophiles know just how tough and resilient life can be. Microbes have been discovered in virtually all four corners of the Earth, including deserts, extreme altitudes, and undersea volcanoes. Insights like these have forced astrobiologists to reconsider the types of environments where life is capable of emerging and flourishing.
And indeed, as a new paper published in Astrobiology suggests, life may even emerge on those planets whose orbits take them out of a solar system's habitable zone — what would likely result in some rather unique and bizarre adaptations.
Odd life on odd planets
Compared to other planets, Earth's orbit is practically a circle. We are firmly planted in the midst of our solar system's so-called Goldilocks zone, which is likely why life flourishes here to the degree that does.
But not all planets are like Earth. As astronomers who study exoplanets are quickly realizing, many terrestrial planets travel along exaggerated elliptical orbits that take them too close or too far away from their parent star. The question that emerges, therefore, is whether or not life can handle these periodic journeys outside the habitable zone.
NASA's Dawn Gelino and Stephen Kane say yes — and that the presence of extremophiles on Earth likely proves it. The only requirement, they say, is that water needs to be present at some point during the planet's orbit.
The researchers suggest that life can adapt and develop countermeasures to survive the harsh conditions found outside of habitable zones. The strategies would essentially involve hiding, hibernating, taking advantage of the good times, and avoiding sterilization.
For example, the researchers suggest that some organisms could drop their metabolism to zero and hibernate in order to survive extended stays in frigid conditions. Similarly, if the planet gets too close to its sun, it could hide inside a protective layer of rock or water.
They also point to studies on Earth which have shown that spores, bacteria, and lichens can survive a variety of conditions — including the ravages of space. And if complex plant or animal life should emerge, it would have to evolve strategies to cope with an extended annual biological clock; these exo-creatures would have to find a way to optimize the time they spend in favorable conditions.
Habitable Zone Gallery
As a result of their research, Gelino and Kane are suggesting that astrobiologists need to revise the traditional parameters of the habitable zone to include those planets who, every once in awhile, leave their cozy confines.
To that end, the team has compiled a handy resource called the "Habitable Zone Gallery." The site calculates the size and distance of the habitable zone for each exoplanetary system that has been discovered, along with a graphical demonstration of each planet's orbit — and they've included those exoplanets that occasionally leave the habitable zone.
The researchers also suggest that life can emerge completely outside Goldilocks zones, such as on moons that orbit around outer gas giants. Though further research is required, they suggest that gas giants may someday have to be included as a potentially habitable zone unto themselves.
Check out the entire study at Astrobiology.
Images via NASA/NASA/JPL-Caltech.