Earth and Venus: Exoplanet Habitable Zone Around Sunlike Stars Bigger

The Earth and Venus, although not very different in size, have had a very different climate history. 

In the future, the Earth may look like Venus. 

Credit: Jeremy Leconte

Earth's place in the solar system is just right.

It's not too hot, like Venus, and it's not too cold, like Mars, and this "Goldilocks zone" of habitability around other stars like the sun just might be bigger than thought, scientists say.

A new study, unveiled today (Dec. 11), expands the habitable zone — the sweet spot in a solar system where liquid water and therefore life could potentially exist — surrounding stars like the sun.

Previous studies on the habitability zone around sunlike stars have placed the innermost edge of so-called Goldilocks zoneat about 0.99 AU (1 AU, or astronomical unit, is the average distance from Earth to the sun, about 93 million miles, or 150 million kilometers).

But a new computer model study pushes that border closer to its parent star, to a distance of about 0.95 AU (about 88 million miles, or 142 million kilometers).

The study in the journal Nature, led by Jeremy Leconte, now a postdoc at the Canadian Institute for Theoretical Astrophysics of the University of Toronto, used 3D computer modeling to find that the runaway greenhouse effect isn't an issue unless the planet is less than 0.95 AU from its star.

The new inner boundary for habitable zones might not make a big difference for scientists trying to determine if an alien planet is habitable, but it does make a big difference for future life on Earth, Leconte said.

Eventually, the sun will become brighter, heating the Earth and potentially creating a runaway greenhouse effect — a feedback loop that eventually causes a planet's oceans to boil away. But that eventuality is long way off, and it may now actually be farther off than previously expected, Leconte suggests.

"For example, if we believe that the limit is at 0.99, it means that Earth would start losing oceans around 150 million years from now," Leconte told reporters.

"Now, with our new estimate, it's not 150 million years, but it's actually 1 billion years, so almost an order of magnitude bigger."



More Information: 
Increased insolation threshold for runaway greenhouse processes on Earth-like planets doi:10.1038/nature12827

ESA ESO: New Goldilocks Planet Found

European astronomers said Monday that they had found what might be the best candidate for a Goldilocks planet yet: a lump of something about 3.6 times as massive as the Earth, circling its star at the right distance for liquid water to exist on its surface — and thus, perhaps, to host life, as we narrowly imagine it.

The planet, known as HD 85512b, is about 36 light years from here, in the constellation Vela. It orbits its star at about a quarter of the distance that Earth circles the Sun, taking 58 days to make a year.

That distance would put it in the star’s so-called habitable zone, if the planet is rocky and has some semblance of an atmosphere — “if everything goes right and you have clouds to shelter you,” as Lisa Kaltenegger of the Harvard-Smithsonian Center for Astrophysics and the Max Planck Institute for Astronomy in Heidelberg, Germany, summarized it.

Astronomers cautioned, however, that it would take years and observations from telescopes not yet built before those assumptions could be tested and a search for signs of life could be undertaken.

Neither humans nor their robot helpers are likely to be dispatched toward Vela anytime soon. But the finding did vault HD 85512b to the top of a list of the handful of Goldilocks candidates.

Habitable Planet in the 'Goldilocks Zone'

An artist rendering provided by Lynette Cook, National Science Foundation, shows a new planet. Astronomers have found a planet that is in the "Goldilocks zone" - just right for life.

Not too hot, not too cold. Not too far from its sun, not too close and it is near Earth - relatively speaking, at 120 trillion miles.

It also makes scientists think that these examples of habitable planets are far more common than they thought

Picture: AP Photo/Zina Deretsky, National Science Foundation