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'Venus Zone' around stars identified, aiding the search for Earth-like worlds beyond our solar system

Scott Sutherland
Meteorologist/Science Writer

Thursday, September 18, 2014, 4:55 PM - The search for Earth-like planets around other stars has taken a step forward recently, thanks to astronomer Stephan Kane and a team of researchers. Their identification of the 'Venus Zone' will go a long way towards helping scientists work out exactly which planets discovered beyond our solar system are the most likely to be potentially habitable.

In the search for extrasolar planets, or exoplanets, astronomers have come up with what they call the 'habitable zone' of a star. This is the region surrounding the star where it's not too warm or too cold - just taking into consideration the amount of heat and radiation from the star - so that it's possible to have liquid water on the surface of any planet that would be orbiting in that zone. This 'not too hot' and 'not too cold' has earned this region the nickname 'the Goldilocks Zone' and a primary goal of NASA's Kepler Telescope mission has been to finding these potentially-habitable worlds.

Just because a planet orbits in this zone, though, does not mean that it's automatically habitable or even potentially-habitable. The planet itself has a big influence on this. If it's too large, it will very likely be more like Neptune, or maybe even Jupiter (if it's big enough). That wouldn't necessarily rule out the possibility of habitable layers of the planet's atmosphere or even habitable moons orbiting the planet, but the planet itself wouldn't be anything like Earth. If the planet is too small, it probably won't be able to hang on to enough atmosphere to be habitable by the standards of life here on Earth. Although we're still trying to determine what happened with Mars' atmosphere over time, it is a fairly good example of this.

Even for an Earth-sized planet, the relative distance within the habitable zone - whether it's closer to the inner edge, the outer edge or somewhere in between - is certainly important, but it may also come down to the thickness and composition of the atmosphere to determine whether we would consider it habitable. Earth is, of course, just at the right spot for the size of the planet and the composition of the atmosphere, while Venus - an Earth-sized planet that's 25 per cent closer to the Sun - is inhospitable to the extreme.

"The Earth is Dr. Jekyll and Venus is Mr. Hyde, and you can't distinguish between the two based only on size," Dr. Kane said in a San Francisco State University news release. "So the question then is how do you define those differences, and how many 'Venuses' is Kepler actually finding?"

RELATED: Colonizing Venus may be more plausible than it sounds

There have already been some examples of exoplanets discovered in their star's habitable zone that have come under dispute, due to how their size and potential atmospheric composition would affect what the surface environment would be like. So, when looking out into the galaxy, searching for exoplanets that may harbour life like us, knowing exactly where an Earth-sized planet would transition from being Earth-like to being Venus-like would help us weed out those that are unsuitable for life.

CLICK BELOW TO WATCH: "So, if the planet is the size of the Earth and it falls in between these two boundaries of the Venus Zone, then we know that it's probably more like Venus than like Earth."

Knowing the 'Venus Zone' isn't only useful for looking out to other star systems. It can also help us with piecing together the history of our own solar system.

"If we find all of these planets in the Venus Zone have a runaway greenhouse-gas effect, then we know that the distance a planet is from its star is a major determining factor," Kane said in the news release. "That's helpful to understanding the history between Venus and Earth."

The study, which has been accepted for publishing in a future issue of Astrophysical Journal Letters, has been pre-published online (click here).

(Images courtesy: NASA/JPL-Caltech/Ames, Chester Harman, Penn State. Video courtesy: SFSU)

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