![]() The outer planet is necessary, Barnes added, to keep the potentially habitable planet’s orbit noncircular. “This constant flexing causes layers inside the planet to rub against each other, producing frictional heating.” When farther from the star, the field is weaker and the planet relaxes into a more spherical shape,” Barnes said. “When the planet is closer to the star, the gravitational field is stronger and the planet is deformed into an American football shape. The habitable zone is that swath of space around a star just right to allow an orbiting rocky planet to sustain liquid water on its surface, thus giving life a chance. Using computer models, the researchers found the effect can occur on older Earth-sized planets in noncircular orbits in the habitable zone of low-mass stars, or those less than one-quarter the mass of the Sun. ![]() ![]() The researchers showed that this phenomenon can take place on exoplanets - those outside the solar system - as well. The effect happens locally, so to speak, on Jupiter’s moons Io and Europa. Tidal heating results from the gravitational push and pull of the outer companion planet on its closer-in neighbor, Barnes said. The lead authors are graduate student Christa Van Laerhoven and planetary scientist Richard Greenberg at the University of Arizona. UW astronomer Rory Barnes is second author of a paper published in the July issue of the Monthly Notices of the Royal Astronomical Society. Over time their molten cores solidify and inner heat-generating activity dwindles, becoming less able to keep the world habitable by regulating carbon dioxide to prevent runaway heating or cooling.īut astronomers at the University of Washington and the University of Arizona have found that for certain planets about the size of our own, the gravitational pull of an outer companion planet could generate enough heat - through a process called tidal heating - to effectively prevent that internal cooling, and extend the inner world’s chance at hosting life. Having a companion in old age is good for people - and, it turns out, might extend the chance for life on certain Earth-sized planets in the cosmos as well. “The sky is mostly dark because cool stars don’t emit much blue light, so the atmosphere doesn’t scatter it.” Rory Barnes, University of Washington “The star would appear about 10 times larger in the sky than our sun, and the crescent is not a moon but a nearby Saturn-sized planet that maintains the tidal heating,” Barnes notes. But what would such a planet look like on its surface? Here, UW astronomer Rory Barnes provides a speculative illustration of a planet in the habitable zone of a star about the size of the sun. For certain ancient planets orbiting smaller, older stars, the gravitational influence of an outer companion planet might generate enough energy through tidal heating to keep the closer-in world habitable even when its own internal fires burn out.
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