Habitable planets: The ideal home in the Goldilocks Zone

An artist's rendition of Nasa's planet-hunting Kepler spacecraft. (AFP photo handout - Nasa/Ames/JPL-Caltech)

An artist's rendition of Nasa's planet-hunting Kepler spacecraft. (AFP photo handout - Nasa/Ames/JPL-Caltech)

It is some of the most sought-after real estate in the universe: the Goldilocks Zone. It is the area around a star in which liquid water could exist on an exoplanet. If the exoplanet were closer to the star, it would evaporate; further away, it would freeze.

Planet hunters the world over have been searching for exoplanets in this fairy-tale region because it is there they expect to find habitable exoplanets, which could hypothetically support human life, or be a place where we could possibly find carbon-based life forms.

On Tuesday, astronomers at the Harvard-Smithsonian Center for Astrophysics announced that they had found eight new habitable exoplanets, two of which the astronomers say are the most similar to Earth so far.

Checking out the neighbours
Before this announcement to a meeting of the American Astronomical Society, there were 14 confirmed habitable exoplanets.
Now that count is 22. A generation ago, we thought Earth was unique: a singular occurrence that allowed for life in the cold, infinite chasm of space.

We thought that our solar system was the only one of its kind in the universe. In fact, to this day, the official definition of “planet” only includes planets in our solar system. The first exoplanet – a planet not in our solar system, but orbiting another star – was detected and confirmed in 1992.

Lead author Guillermo Torres said of their discovery: “Most of these planets have a good chance of being rocky, like Earth.”

An important condition for life is sunlight: too much and life burns, too little and it freezes. The centre said the two most Earthlike candidates, Kepler-438b and Kepler-442b, have about 40% more light and 30% less light respectively than we get on Earth, putting their chances of being in the habitable zone at about 70% and 97%.

Mission extended
But it is not as simple as being the right size, rocky and in the Goldilocks Zone. Our blue and green globe has a cushioning atmosphere of nitrogen with a soupçon of oxygen, so we can breathe, and a magnetic core creating an invisible field that protects us from the unrelenting cosmic radiation.

“We don’t know for sure whether any of the planets in our sample are truly habitable,” said second author David Kipping. “All we can say is that they are promising candidates.”

Most of this is as a result of Nasa’s Kepler spacecraft, a planet-hunting space observatory.

Nasa on Tuesday announced the 1 000th confirmed exoplanet discovered by Kepler. Scientists are still sifting through the glut of information the spacecraft transmitted back to Earth.

Launched in 2009, it was said Nasa would decommission the spacecraft in 2013, as the second of its four reaction wheels failed. But Nasa approved the K2 “Second Light” mission for the space observatory late last year, which will allow it to continue collecting planet data, and in December announced that the K2 mission had detected its first exoplanet.

Sarah Wild

Sarah Wild

Sarah Wild is a multiaward-winning science journalist. She studied physics, electronics and English literature at Rhodes University in an effort to make herself unemployable. It didn't work and she now writes about particle physics, cosmology and everything in between.In 2012, she published her first full-length non-fiction book Searching African Skies: The Square Kilometre Array and South Africa's Quest to Hear the Songs of the Stars, and in 2013 she was named the best science journalist in Africa by Siemens in their 2013 Pan-African Profiles Awards. Read more from Sarah Wild

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