Galaxy's Abundance Of Gaseous Mini-Neptunes, Super-Earths Makes Possibility Of Life There Impractical

By Ben Wolford on January 12, 2014 12:52 PM EST

The Super-Earth 55 Cancri e, depicted by a NASA artist, zips around its sun every 18 hours, giving it an extremely short year and an extremely hot crust. (Photo: NASA/JPL-Caltech)

The Super-Earth 55 Cancri e, depicted by a NASA artist, zips around its sun every 18 hours, giving it an extremely short year and an extremely hot crust. Its surface is likely water in a superheated state between liquid and gas, and its atmosphere is likely steam. Nothing on Earth could live there. (Photo: NASA/JPL-Caltech)

Exoplanets aren't like the eight planets in our solar system, a distinguished astronomer told his colleagues at the annual meeting of the American Astronomical Society in Washington, D.C. last week. In fact, somewhere around 85 percent of them fall in a planetary gray zone between our rocky, smallish Earth and the fairly large, gaseous Neptune — meaning they aren't necessarily ideal for life as we know it.

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As astronomers pry the heavens for more examples of alien planets, underlying their science is a deeper question about life. Bold in its implications — that perhaps we are not unique — the inquiry has so far been foiled by the limitations of our technology and the universe's apparent preference for planets larger than earth (called super-Earths) and smaller than Neptune (mini-Neptunes). It is likely, though yet unknown, that Earth-like life could exist on these planets.

"We know very little about how life got started and in what environments it might flourish," Geoff Marcy, astronomer at the University of California, Berkeley, said, according to The Washington Post. Marcy is known for discovering more exoplanets than anybody else. "We're really in the dark about the biology aspect of these planets."

Tracking down planets outside our solar system is a tricky business. They're so small that astronomers have to wait until one of them passes in front of its star, causing a trademark flicker that tells scientists scant information about the planet's size, orbital distance, and density. From that, they can hypothesize about the gravity, composition, and surface characteristics of these planets. According to Marcy's findings, it doesn't look like many of the hundreds of solar systems discovered so far look anything like our own.

As The Post, which covered the astronomers conference, put it: "Marcy noted that these planets orbit close to their parent stars and that it is possible, with advances in instrument sensitivity, that scientists will discover an abundance of small, rocky planets at more distant orbits. ... But that's not what we see so far." So far, Marcy says, planets that are twice the diameter of Earth or smaller are kind of like Earth, dense and rocky. Any bigger, and they become far less dense and more like Neptune, which is gaseous except for a small, rocky core. The pressure at the core of these planets would be immense.

Others are more hopeful that Earth-like planets exist. One astronomer at the same conference even suggested there are super-Earths that look a lot like ours, just bigger, according to Space.com. Nicolas Cowan of Northwestern University says scientists have often thought that any water on a super-Earth would completely flood the surface, like the planet 55 Cancri e, pictured above. But Cowan argues that the heightened gravity of these planets would force the water into the mantle, exposing continents and creating a more temperate climate. "We can put 80 times more water on a super-Earth and still have its surface look like Earth," said Cowan in a statement. And since the latest census of planets this size numbers around 40 billion, maybe such a planet is possible after all.

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