Stars’ Habitable Zones Are Larger Than Previously Thought

By Bill Andrews | December 11, 2013 12:09 pm


Good news for those searching for life elsewhere in the universe: a study released today suggests that planets orbiting surprisingly close to their stars can remain livable. This extension of the so-called habitable zone, based on computer modeling, is also important for what it implies about our own planet’s future habitability.

Studying habitable zones has always been tricky, because there’s only one habitable planet we know of—our own. Still, astronomers have established the general boundaries for what they call a star’s habitable zone, the donut-shaped region around that star where an Earth-like planet could host liquid water, necessary for life as we know it. At the zone’s outer edge water freezes from the cold, and at the inner edge it evaporates from the heat; conditions are “just right” inside the zone, hence the area’s other common nickname: the Goldilocks zone.

Changing Conditions

But it’s not as simple as all that, because stars’ output changes over time. The sun, for example, has been getting steadily brighter and hotter over the millennia. So scientists have used complicated models to determine the precise boundaries of any given star’s habitable zone over time.

But, as it turns out, they weren’t complicated enough. Today’s paper used 3-D climate models to determine just how hot a planet can get before it slips out of the habitable zone, and found that it can be hotter than the older, 1-D models suggested. (The new 3-D approach took into consideration things like clouds—a fairly important climate feature, if you think about it.)

So, whereas previously a sun-like star was believed to have a habitable zone starting at about 0.99 astronomical units away (where 1 AU is the average Sun-Earth distance of about 93 million miles), now it starts a bit closer, at 0.95 AU. The findings are reported today in Nature.

Pushing the Boundaries

That might not seem like much, but it widens a sun-like star’s habitable zone by millions of miles. Thus it should, theoretically, be that much more likely for researchers to find an extrasolar planet out there with conditions suitable for life.

And the results also hit closer to home. With the sun’s ever-increasing output, we know there will come a time when its habitable zone leaves Earth behind, rendering our own planet uninhabitable. This study, which proved planets are more heat-resistant than thought, also suggests that “we” won’t have to worry about our world losing all its liquid water for at least another billion years. Phew!


Image credit Petigura/UC Berkeley, Howard/UH-Manoa, Marcy/UC Berkeley


CATEGORIZED UNDER: select, Space & Physics
  • Ender Wiggin

    Yaaay, another nine hundred million years to procrastinate!

  • S Ibrahim

    Good to know..;-)
    “” “we” won’t have to worry about our world losing all its liquid water for at least another billion years. Phew.””
    Now I can sleep peacefully….. And dream about a planet like earth.

  • Buddy199

    With so many possible locations for life, some of which you would assume would be technologically advanced, why haven’t we detected even one unmistakable signal?

    • Wil Post

      Considering it took over 3 billion years for a technological species to emerge once life began on Earth… do I really need to point this out? I had a whole thing typed out then decided it’ll probably fall on deaf ears anyway.

      • Buddy199

        It’s a simple math problem, but thanks for the condescension.

        • Gary Carkeek

          How far into deep space could our current output be received and proved to be of artificial origin by a society with our own present level of technology?
          Surely the question hangs on this?

    • Michael Geil

      Considering the vastness of space, the question we need to answer is what is the ultimate universal tool for communication. Right now we use light and radio waves. But that would be similar to using smoke signals when comparing what the real answer should be. Inevitably we will find ways to bypass space by distortion or other means that will allow for instant relay of information beyond our galaxy. When we do we will find what we are looking for. Until then we just have to imagine and innovative.

  • OpinionLA

    So many places for people to live!

    • Jon

      There’s so much more room for activities!

  • stevlich

    This is all nonsensical speculation until alien life is discovered which will be never because NASA has a conspiracy to never confirm extraterrestrial life even if it were walking and as big as an elephant.

    • Michael Geil

      There are extraterrestrial microbes living on the outskirts of our atmosphere that were brought there by asteroids.

  • luke101

    This exercise is useless and naive, until someone can tell me how we are to travel to distant stars. Until then, we are far more likely to colonize the Moon and Mars than search for “Eden” in far away galaxies. Under-the-surface colonies are possible now.


Discover's Newsletter

Sign up to get the latest science news delivered weekly right to your inbox!


See More

Collapse bottom bar