10 December 2011
Our Earth is a Goldilocks planet. It’s neither too cold nor too hot but right in the habitable zone. Add another parameter that’s needed to be just right to incubate life on our world: plate tectonics.
A team of geophysicists is modeling conditions that favor cruising plates on planets outside of our solar system, known as exoplanets, which might clue scientists into which of those worlds harbor complex life.
“We cannot fly to the planets and investigate if they have plate tectonics,” said Lena Noack, a geophysicist from the University of Münster and IfP DLR Berlin, in Berlin, Germany.
Her team’s model can look for plate movements on distant planetary bodies using only the bits of information we do have—such as a planet’s mass and weight. Noack presented a poster on the project Tuesday morning at the American Geophysical Union’s Fall Meeting.
Noack looked at the influence of how easily the mantle flows, what size the planet needs to be to support that flow, the influence of internal heating, how water affects the mantle’s movement, and the relationship between surface temperature and how yielding a planet’s crust is.
On Earth, when one plate slides beneath another, the addition of cool crust sustains the churning motion of the mantle, Noack said. That motion creates a magnetic field surrounding us, which protects life from harmful radiation. The same movement recycles minerals in the Earth’s crust, which are essential to a rich, diverse biosphere, Noack explained. Finally, recycling carbon out of the planet’s atmosphere prevents a run-away greenhouse effect, keeping Earth in that Goldilocks zone of not-too-hot, yet not-too-cold.
“If you had not had plate tectonics on Earth, we probably would not have life as we know it,” Noack said.
Planets that meet all the parameters for plate movements would be rare in the universe. But it happened on Earth, so it may have happened elsewhere.
One place that has piqued scientists’ curiosity is the newly announced Kepler 22b. The publicity surrounding this newest world sparked discussion around Noack’s poster.
The new planet is the smallest earth-like planet reported yet. Like Earth, it orbits its sun in the Goldilocks habitable zone. However the optimal planetary mass for tectonic plates is between the equivalents of 0.5 to 5 Earths, Noack said, whereas Kepler 22b’s mass is probably more than 10 Earth masses. Based on that strike against plate tectonics occurring on the new-found world, Noack doubts we’ve discovered the home of our galactic neighbors.
Still, Noack said she is hopeful we will discover extraterrestrial life in her lifetime. It may be tricky given how little information we can gather about planets outside of our solar system. Instead, we listen to distant worlds and hope to hear a transmission from another civilization.
“If you don’t get signs of life, that doesn’t mean it isn’t there,” Noack said. “But maybe they are too intelligent to broadcast into space.”
-Marissa Fessenden is a science communication graduate student at UC Santa Cruz