Scientists may have just gotten some encouragement in their search for other habitable worlds. According to new research, super-Earths likely harbor long-lasting oceans, a hallmark recipe for life on far-away planets.
"When people consider whether a planet is in the habitable zone, they think about its distance from the star and its temperature. However, they should also think about oceans, and look at super-Earths to find a good sailing or surfing destination," lead author Laura Schaefer of the Harvard-Smithsonian Center for Astrophysics (CfA) said in a statement.
Geologic evidence indicates that Earth's oceans have existed for nearly the entire history of our world - flooding our planet earlier than we thought - though exactly how they formed still largely remains a mystery. One recent study even suggests that Earth created its own bodies of water from within via a series of geologic process at its interior - in addition to help from icy comets, which conventional theory argues is the source of liquid water.
So can the same be said of super-Earths - planets up to five times the mass (or 1.5 times the size) of Earth? The CfA team says yes, and that once oceans are established on these massive planets, they can persist for billions of years.
While liquid water makes up a whopping 70 percent of Earth's surface, the scientists note that it actually is only a fraction of its overall bulk. The majority of Earth is composed of rock and iron, whereas only a tenth percent is water. It seems strange then that our oceans are so vast. But water doesn't just exist on the surface.
The research team explains that Earth's mantle holds so much water - kept underground by plate tectonics and subduction of the ocean seafloor - that it's enough to fill several oceans. The theory is that via a process called volcanism, Earth essentially recycles its oceans, constantly sucking water down to its interior then to shoot it back up to the surface and create our Blue Planet.
According to this latest study, which relied on computer simulations, this recycling process can occur on super-Earths as well. Astonishingly, planets two to four times the mass of Earth are even better at establishing and maintaining oceans than our Earth, lasting for at least 10 billion years. That is, once the planet cooled enough for its crust to solidify and oceans to form. But these chemical processes take time.
Researchers found that a super-Earth five times the mass of Earth, the largest planet studied, didn't develop oceans until about a billion years after it first formed. That's because it had a thicker crust and lithosphere which delayed the start of volcanic outgassing. (Scroll to read on...)
"This suggests that if you want to look for life, you should look at older super-Earths," Schaefer said. Specifically, she says scientists should look toward planets that are about five and a half billion years old - a billion years older than Earth - in the hunt for habitable super-Earths.
The use of the ground-based telescope called the Nordic Optical Telescope, on the island of La Palma, Spain, may make detection of such worlds easier. Last month researchers were able to for the first time measure more accurately a transit of the known super-Earth 55 Cancri e, located 40 light-years away, in front of a nearby Sun-like star.
This ground-based technology, along with the results of the new study, spell hope that we may soon discover more super-Earths in the next several years, perhaps with promising conditions and vast oceans teeming with life.
The findings were presented Monday at the 225th meeting of the American Astronomical Society in Seattle.
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