A widely accepted theory explaining the formation of Earth’s moon is a collision with another rocky planet about the size of Mars that created a partially vaporized disk around Earth which eventually formed a satellite with a radius more than one-quarter of Earth’s. While other planets in our solar system have moons, only ours is so large in comparison to its planet … and only Earth is home to advanced forms of life -- or any life at all, as far as we know. Could a large moon be the key to life? A new study proposes just that – and suggests the search for life should focus on Earth-sized exoplanets with massive satellites.
“By understanding moon formations, we have a better constraint on what to look for when searching for Earth-like planets. We expect that exomoons [moons orbiting planets outside our solar system] should be everywhere, but so far we haven’t confirmed any. Our constraints will be helpful for future observations.”
In a paper published in the journal Nature Communications, Miki Nakajima, an assistant professor of earth and environmental sciences at the University of Rochester, describes how her team of researchers at the Tokyo Institute of Technology and the University of Arizona developed a simulation to recreate impacts like the one that formed our Moon. The simulation allowed them to vary the size of the Earthlike planet and its composition – rocky or icy – and predict what kind of disc would form around it. Those creating a partially vaporized disk would eventually get a large moon and should be good candidates for life.
“We found that if the planet is too massive, these impacts produce completely vapor disks because impacts between massive planets are generally more energetic than those between small planets.”
The simulation showed large icy planets created fully vaporized discs and were easily dragged back into their host planet. The team also found that rocky planets larger than six times the mass of Earth and icy planets larger than one Earth mass generally produced fully vaporized disks. Thus the ideal life candidate is a rocky planet less than six times the size of Earth with a large moon capable of helping life survive on its planet the way our Moon does – controlling tides on the watery surface, affecting the length of a day which affects the biological life cycles of living creatures, stabilizes the rotation of the planet to make living less traumatic.
If there are any SETI researchers reading this, Miki Nakajima has this advice:
“The exoplanet search has typically been focused on planets larger than six earth masses. We are proposing that instead we should look at smaller planets because they are probably better candidates to host fractionally large moons.”
Do they exist? Will we find them?
Before they find us?