Washington: Stars that resemble our own Sun are scattered around the Milky Way – and a new study has suggested that any planets orbiting those stars may very well be hotter and more dynamic than Earth.
That’s because the interiors of any terrestrial planets in these systems are likely warmer than Earth -- up to 25 percent warmer, which would make them more geologically active and more likely to retain enough liquid water to support life, at least in its microbial form.
The preliminary finding comes from geologists and astronomers at Ohio State University who have teamed up to search for alien life in a new way.
They studied eight “solar twins” of our Sun -- stars that very closely match the Sun in size, age, and overall composition -- in order to measure the amounts of radioactive elements they contain. Those stars came from a dataset recorded by the High Accuracy Radial Velocity Planet Searcher spectrometer at the European Southern Observatory in Chile.
They searched the solar twins for elements such as thorium and uranium, which are essential to Earth’s plate tectonics because they warm our planet’s interior. Plate tectonics helps maintain water on the surface of the Earth, so the existence of plate tectonics is sometimes taken as an indicator of a planet’s hospitality to life.
Of the eight solar twins they’ve studied so far, seven appear to contain much more thorium than our Sun -- which suggests that any planets orbiting those stars probably contain more thorium, too. That, in turn, means that the interior of the planets are probably warmer than ours.
For example, one star in the survey contains 2.5 times more thorium than our Sun, said Ohio State doctoral student Cayman Unterborn. According to his measurements, terrestrial planets that formed around that star probably generate 25 percent more internal heat than Earth does, allowing for plate tectonics to persist longer through a planet’s history, giving more time for life to arise.
“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 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,” he added.
His advisor, Wendy Panero, associate professor in the School of Earth Sciences at Ohio State, explained that radioactive elements such as thorium, uranium, and potassium are present within Earth’s mantle. These elements heat the planet from the inside, in a way that is completely separate from the heat emanating from Earth’s core.
On Earth, most of the heat from radioactive decay comes from uranium. Planets rich in thorium, which is more energetic than uranium and has a longer half-life, would “run” hotter and remain hot longer, Unterborn said, which gives them more time to develop life.
Jennifer Johnson, associate professor of astronomy at Ohio State and co-author of the study, cautioned that the results are preliminary. “All signs are pointing to yes -- that there is a difference in the abundance of radioactive elements in these stars, but we need to see how robust the result is,” she said.
Unterborn presented the results at the American Geophysical Union meeting in San Francisco this week.