NASA has announced confirmation of the most Earth-like planet yet. Known as Kepler-452b, it is a “super Earth” about 60% larger than our home planet. We don’t know its mass, but if it has a similar composition to Earth, then its mass is about 4 times Earth’s, and its surface gravity is about 1.6 gees. While that’s not too similar to Earth, what’s remarkable is its orbit. Kepler is a G2 star only 4% more massive than our own Sun, and this new planet orbits at a radius only 5% larger than Earths. The amount of light 452b receives from its star is almost identical to Earth.

We don’t have any direct evidence regarding 452b’s composition. It could be a cold dry world like Mars, or have a thick and toxic atmosphere like Venus. But it could also be a wet world with an atmosphere similar to ours. If that’s the case, then it would have a temperature similar to Earth’s, with liquid water lakes or oceans. It could have a strong magnetic field and be geologically active. It is within the realm of possibility that the planet would be habitable by terrestrial organisms. Kepler 452 is about 1.5 billion years older than our Sun, so this newly announced planet has been within the habitable zone of its star for 6 billion years, which is plenty of time for life to have evolved.

It’s important not to read too much into this. Kepler-452b could be completely inhospitable for lots of reasons, and we still don’t know if it is easy or difficult for life to arise on potentially habitable worlds. But this discovery does make one thing quite clear. Sun-like stars do indeed have Earth-like planets orbiting their habitable zones. Given the statistics of the exoplanets we’ve found thus far, such planets appear to be common. Perhaps extraordinarily so.

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The search for planets around other stars has led to the discovery of over 800 extrasolar planets.  Most of these are large, Jupiter type planets orbiting close to their star since those planets are easier to detect.  Our techniques are getting better, however, and that means not only more planets discovered every year, but also smaller planets.

In the figure below I’ve plotted the masses of discovered planets vs. the year of their discovery.   I’ve only plotted planets that have around 10 earth masses or less, which are often called “super earths” because they are Earth-like (rocky) planets with a larger mass than Earth.

What is interesting about this graph is that the minimum mass planet of each year keeps getting smaller, to the point that we are now discovering planets almost as small as Earth.  Within the next year or so we will start discovering planets of Earth mass or smaller, and eventually one of those planets will be in the habitable zone of its star.  We will have discovered the first “new Earth.”

Of course, even when we discover an Earth mass planet with an Earth-like temperature, that doesn’t guarantee that it will have life.  But what it will show is that planets like ours are not alone in the universe.  Our pale blue dot will have sisters.

We’ve come a long way since the first extra-solar planet was discovered in 1995. Within a decade of that discovery, we will likely identify dozens of earth-like worlds, which is nothing short of amazing.

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