The Recipe for Alien Earths: Scientists Examine Earth-like Worlds

How to assemble Earth: Take elements, stir, and dash with water delivered by asteroids. Scientists are taking a closer look at how Earth-like planets are made in order to continue their hunt for exoplanets that have the likeliest chance at supporting life.

"Our solar system is not as unique as we might have thought," said Courtney Dressing, one of the researchers, in a news release. "It looks like rocky exoplanets use the same basic ingredients."

In this case, the researchers accurately measured the masses of small, Earth-sized worlds with the help of the HARPS-North instrument in the Canary Islands. The scientists focused on planets that were less than two times the diameter of Earth, studying a few planets very well. Recently, the researchers targeted KEpler-93b, a planet just 1.5 times the size of Earth in a tight, 4.7-day orbit around its star.

The researchers compared all ten known exoplanets with a diameter less than 2.7 times Earth's that had accurately measured masses. In the end, they found that the five planets with diameters smaller than 1.6 times Earth showed a tight relationship between mass and size. Not only that, but Venus and Earth fit into the same line, suggesting that all of these worlds have similar rock-iron compositions.

For the larger and more massive exoplanets, their densities were significantly lower. This means that they included a large fraction of water or other volatiles, hydrogen and/or helium. They also showed more diverse compositions rather than fitting into a single group like the smaller terrestrial worlds.

"To find a truly Earth-like world, we should focus on planets less than 1.6 times the size of Earth, because those are the rocky worlds," said Dressing.

The findings reveal a bit more about where to find Earth-like worlds. More specifically, it shows researchers which worlds to target for further study in other galaxies.

The findings were presented at a meeting of the American Astronomical Society.

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