On Earth, greenhouse gases are blamed for climate change, but elsewhere in the cosmos, they could help a planet not at all like Earth be habitable, one scientist suggests.
The search for life outside our solar system can, at times, sound a bit like a broken record. We are looking for planets not too much bigger or smaller than ours, circling stars not too different from our sun, orbiting at a distance not too far out or close in.
This, astronomers say, is the "Goldilocks zone," where everything is just right for life. For that reason, finding an Earth-like planet orbiting a sun-like star remains, in many ways, the holy grail of exoplanet research. After all, we know it works here.
Now, a new paper in the journal Science is suggesting that the actual Goldilocks zone might be much different from what we earthlings imagine. Indeed, habitable planets could be much farther out than Earth or significantly closer in if other factors are taken into account, writes Sara Seager of the Massachusetts Institute of Technology in Cambridge, Mass.
The point, she says, is to remember the spectacular variability of nature and consider all the different ways life might find a foothold in the cosmos.
Take greenhouse gases, for example. Here on Earth, as humans introduce more into the atmosphere, these gases are mostly blamed for heating up the climate at unusually fast rates. But, in the right regulation, they serve a vital purpose to life on Earth: They keep the planet warm.
Earth's mass has helped it hold on to these gases, but it's not nearly massive enough to hold on to hydrogen – a much more potent greenhouse gas than the ones at work here. Yet other planets – super-Earths several times more massive – perhaps could hold on to their stocks of hydrogen. If so, they could orbit their stars much farther out than Earth does and still have a warm surface.
In other words, such a super-Earth would receive less heat from its star than we do from ours, but it would hold onto whatever heat it does receive much more effectively.