Companion planets can increase old worlds' chance at life

Companion planets can increase old worlds’ chance at life
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. 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. “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. “The sky is mostly dark because cool stars don’t emit much blue light, so the atmosphere doesn’t scatter it.” Credit: Rory Barnes, University of Washington

(Phys.org) —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.


But astronomers at the University of Washington and the University of Arizona have found that for certain about the size of our own, the gravitational pull of an outer companion planet could generate enough heat—through a process called —to effectively prevent that internal cooling, and extend the inner world's chance at hosting life.


Tidal heating results from the gravitational push and pull of the outer companion planet on its closer-in neighbor, Barnes said. The effect happens locally, so to speak, on Jupiter's moons Io and Europa. The researchers showed that this phenomenon can take place on exoplanets—those outside the solar system—as well.



The outer planet is necessary, Barnes added, to keep the potentially habitable planet's orbit noncircular. When a planet's orbit is circular, the from its host star is constant, so its shape never changes, and there is no tidal heating.




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Ancient worlds could be kept 'alive' by gravitational nudges

More information: Tides, planetary companions, and habitability: habitability in the habitable zone of low-mass stars, MNRAS (July 1, 2014) 441 (3): 1888-1898. http://mnras.oxfordjournals.org/content/441/3/1888

The complete paper is also available on Arxiv: http://arxiv.org/pdf/1401.7221v1.pdf

Citation: Companion planets can increase old worlds' chance at life (2014, August 1) retrieved 28 May 2020 from https://phys.org/news/2014-08-companion-planets-worlds-chance-life.html

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