Using computer simulations, researchers have determined that when giant stars like our sun die, they lose mass and swell in size and intense solar winds spread heat to surrounding planets making them uninhabitable.
Planets like Earth reside in the “Goldilocks Zone,” is “just right,” where a planet sits the perfect distance from its sun (host star) allowing for liquid water to exist on the surface. This makes them habitable, fit for life. When a star like our sun dies, every 9 billion years, this zone shifts outward and the zone changes. Habitable planets become uninhabitable. Planets outside of the zone that were frozen, warm and may become habitable.
Earth has been in the “Goldilocks Zone” for 4.5 billion years. It’s only a matter of time when our sun dies off, growing larger and hotter engulfing Mercury and Venus, turning Earth and Mars into hot barren, uninhabitable rocks.
Ramses M. Ramirez, research associate, from the Carl Sagan Institute at Cornell University and team member explains,
Our model predicts that when stars eventually leave the “main-sequence” of stellar evolution, becoming red giants, the habitable zone (HZ) expands outward. The HZ is currently in a region that approximately spans between just beyond Venus’ orbit to just beyond Mar’s orbit. However, during the red giant stage, which for our sun will occur some 7 billion or so from now, stars will get much bigger and brighter, so the HZ will move outward to the outer regions of the stellar system, during which time outer worlds and moons will be within it for some time.
As the zone shifts, it would cover Jupiter and Saturn. However, Jupiter’s only water in floating clouds and Saturn is made entirely of gas. The warming, though, would affect their moons, which would be more conducive to primitive life.
Jupiter’s moon Europa and Saturn’s moon Enceladus may have oceans beneath their surface layers, much like that found in the Arctic. Primitive life may be found underneath that ice, as it thaws. This could begin a new evolutionary lifecycle.
Any initially frozen worlds (e.g. Europa and Enceladus analogues) would melt, allowing any pre-existing subsurface life to be potentially detected. Thus, the red giant stage may be akin to giving a “second wind” to life in the stellar system.
The scientists’ models suggest that in the Universe, in our solar system, a dying star has already brought frozen planets back to life. Actually, the team has identified 23 red giant stars within 100 light years of Earth, which could be warming up with new life.
Lisa Kaltenegger, Director of the Carl Sagan Institute and researcher on the study, says,
In the far future, such worlds could become habitable around small red suns for billions of years, maybe even starting life, just like Earth. That makes me very optimistic for the chances for life in the long run.