Studying the cosmos, we know that low-mass M-class stars are among the most common throughout the universe; or rather, scientists know that.
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There are so many favorable conditions that are set up by smaller stars.
However, the habitable zone for smaller, dimmer stars – the region in which an orbiting planet would receive the amount of heat that is necessary to keep life-friendly moisture in a liquid state on the surface – lies fairly close in.
The closer orbital distance also involves a greater gravitational pull on the planet, which could cause such planets to become tidally locked with their host star, with one side always facing the star as the planet orbits.
Small planets dangerously close to their parent stars could still possess a magnetic field that could protect evolving life, astronomers say.
Could magnetic fields be protecting life on other planets? ‘The question I wanted to ask is, around these small stars, where people are going to look for planets, are these planets going to be roasted by gravitational tides?’
However, he says, computer simulations he and Driscoll performed suggest that far from being damaging to a planet’s magnetic field, tidal heating might actually give it a boost – and thus improve the habitability prospects for a planet.
The research combined models of orbital interactions and heating by Rory Barnes, assistant professor of astronomy, with those of thermal evolution of planetary interiors done by Driscoll, who began this work as a University of Washington postdoctoral fellow and is now a geophysicist at the Carnegie Institution for Science in Washington, DC. This phenomenon creates tidally generated heat inside the planet, also known as “tidal heating”, and drives volcanic activity. By merging their models, they were able, Barnes said, “to produce a more realistic picture of what is happening inside these planets”. The tidal heating does not harm planets.
There has been a general feeling among the cosmologists that tidally-bolted planets are unrealistic to have defensive magnetic fields “and in this manner are totally helpless before their star”.
The more tidal heating a planetary mantle experiences, the better it is at dissipating its heat, thereby cooling the core, which in turn helps create the magnetic field.
Study leader Peter Driscoll and fellow researchers argue that, contrary to these assumptions, their simulations showed that it is perfectly possible for such planets to form magnetic fields. This blocks a larger fraction of the light than if they transited a more massive star.
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The team also found that planets that begin with noncircular orbits and tidal heating eventually settle into circular orbits with no tidal heating. “In the future, exoplanetary magnetic fields could be observable, so we expect there to be a growing interest in this field going forward”.
