Wait, what? Astronomers at Ohio State University have concluded that there could be solar systems more habitable than ours. OSU reports that planets orbiting stars that resemble our own sun may be hotter and more dynamic than Earth. In fact, the interiors of any terrestrial planets in these systems could be 25 percent warmer than Earth. If this is true, these planets would be more geologically active and more likely to hold enough liquid water to support life (at least in its microbial form).
Researchers examined eight “solar twins” of our sun (stars that resemble the sun in size, age and overall composition) in order to determine the amounts of radioactive elements they contain. The solar twins came from a dataset obtained by the High Accuracy Radial Velocity Planet Searcher spectrometer at the European Southern Observatory in Chile.
Researchers were looking for elements such as thorium and uranium, which are key to Earth’s plate tectonics because they are key ingredients in the warming of our planet’s interior. Since plate tectonics contribute to the existence of water on the surface of the Earth, the existence of plate tectonics often indicates whether or not a planet could be hospitable to some form of life.
Seven of the eight solar twins were found to contain a lot more thorium than our sun, suggesting that any planets orbiting those stars probably hold more thorium, as well. This also suggests that the interior of the planets are most likely hotter than ours.
One of the solar twins contains 2.5 times more thorium than our sun. Planets that formed around that particular star likely create 25 percent more internal heat than our own planets does, giving plate tectonics the opportunity to endure longer through a planet’s history. The longer plate tectonics exist, the more time life has to appear.
“If it turns out that these planets are warmer than we previously thought, then we can effectively increase the size of the habitable zone around these stars by pushing the habitable zone farther from the host star, and consider more of those planets hospitable to microbial life,” said Ohio State doctoral student Cayman Unterborn. “At this point, all we can say for sure is that there is some natural variation in the amount of radioactive elements inside stars like ours. With only nine samples including the sun, we can’t say much about the full extent of that variation throughout the galaxy. But from what we know about planet formation, we do know that the planets around those stars probably exhibit the same variation, which has implications for the possibility of life.”
Radioactive elements such as thorium, uranium and potassium exist within Earth’s mantle. These elements warm the planet from the inside, in a manner that is completely separate from the heat emerging from Earth’s core.
“The core is hot because it started out hot,” said Wendy Panero, associate professor in the School of Earth Sciences at Ohio State. “But the core isn’t our only heat source. A comparable contributor is the slow radioactive decay of elements that were here when the Earth formed. Without radioactivity, there wouldn’t be enough heat to drive the plate tectonics that maintains surface oceans on Earth.”
While the relationship between plate tectonics and surface water is not fully understood, scientists theorize that the same forces of heat convention in the mantle that alter our planet’s crust also manage the amount of water in the oceans, too.
“It seems that if a planet is to retain an ocean over geologic timescales, it needs some kind of crust ‘recycling system,’ and for us that’s mantle convection,” Mr. Unterborn added.
Some types of microbial life also rely on subsurface heat to exist. Microbes known as archaea live off of the heat coming from deep inside the Earth. While on Earth, a lot of the heat from radioactive decay comes from uranium, thorium-rich planets are hotter and remain hot longer.
“It all starts with supernovae. The elements created in a supernova determine the materials that are available for new stars and planets to form. The solar twins we studied are scattered around the galaxy, so they all formed from different supernovae. It just so happens that they had more thorium available when they formed than we did,” Mr. Unterborn said.
Researchers warn that these results are untested and that additional studies need to be conducted in order to fine tune conclusions and readjust the accuracy of computer models.