If we're learning one thing in this golden age of planet hunting, it's that our galaxy
is home to a wide diversity of other worlds.
We've yet to find another earth, but we're getting closer.
That's because of a growing class of planet detections known as "super earths."
These planets have a mass higher than that of Earth, but substantially lower than our
Neptune, at around ten times the mass of earth.
At the higher end of the mass scale, these planets are often referred to as mini-Neptunes
or gas dwarfs.
It's those at the lower end of the scale that have sparked our imaginations.
Take the star system called Gliese 667, 22 light years from Earth.
The central point in this image is actually two stars, A and B.
There's also a third, Gliese 667C.
It's the bright finger that juts out to the lower left of the two main stars.
That's where astronomers have found a solar system.
If you could visit one of the planets there, you'd experience the curious spectacle of
three suns rising.
They are part of an elaborate sky dance of stars and planets.
Planet E, pictured here as a crescent, is one of at least seven planets.
They were recently discovered by astronomers at the European Southern Observatory, on the
mountaintops of Chile.
By unraveling the pattern of wobbles in the star's light, they have determined that three
out of seven planets lie within the habitable zone, the range of distances in which there
is enough heat from the star to allow liquid water to flow, but not so much that it would
boil it off.
Sentient beings in residence here might consider the sight of just one sun rising to be boring.
Certainly their world is anything but.
Their parent star is slightly fainter and cooler than our sun.
That means that the habitable zone is closer and narrower than in our solar system.
In fact, it would fit entirely within the orbit of our Mercury.
Remarkably, the three worlds that are crammed into this zone are all considered to be rocky
super earths.
This is the first time that three such planets have been spotted within the same habitable
zone.
Of course, that does necessarily mean they are earth-like.
Our planet shows that it may take a range of specific characteristics to nurture life,
a magnetic field to deflect solar outbursts, a stable rotation, an active geology, and
just the right amount of water vapor and carbon dioxide in the atmosphere to regulate surface
temperatures.
There is one other solar system that may well have what it takes.
The Kepler space telescope has a star in its sights that is well beyond our solar neighborhood.
Kepler 62 is considered to be "sun-like."
It weighs in at 69% the mass of our sun, with a radius of 64%.
Astronomers have discovered five planets orbiting the star, based on subtle dips in its light
as the planets pass between the star and earth.
Two of them, planets E and F are likely solid planets that lie within the star's habitable
zone.
The size of these planets is still uncertain.
They could be several tens of times the mass of Earth.
And the larger they are, the less likely they are to be life bearing.
Still, these Super Earth discoveries are part of an ever-growing diversity of planets known
to grace our galaxy.
No doubt there are planets, somewhere out there, that have the right characteristics
to be called "Earth-like."