Astronomers looking for signs of life beyond Earth often try to study star systems that are similar to our own. But a new study published in the Astrophysical Journal says that scientists should be studying red giants or dying stars for alien life. Lead author Lisa Kaltenegger, director of the Carl Sagan Institute at the Cornell University, said in a statement that red giants could turn many places into “habitable worlds.”
Life may move from Earth to Saturn, but when?
When a star gets old and runs out of fuel, it starts burning helium instead of hydrogen. Helium is far more potent, increasing the star’s energy output. As a result, the star swells up to become hundreds of times larger than its original size, swallowing up planets that are too close. A lot of stars eventually become red giants and remain that way for billions of years, reports Space.com.
Even though the dying star engulfs planets that orbit too close, it could turn distant planets located in frigid locations into havens for life. For instance, our own sun is currently a yellow dwarf star. In about 4 billion years, it will have used up most of the hydrogen at its core, and will start burning helium. In 7.5 billion years, it will swell to about 200 times its current size, engulfing Mercury and Venus. It will render the Earth inhabitable.
Planets near red giants could remain habitable for 9 billion years
But currently frigid locations like the icy moons of Saturn, Pluto and its moon Charon, and Neptune’s moon Triton could become habitable, with just the right temperature to host liquid water on the surface and support life. Researchers estimate that planets around dying stars could remain habitable for up to 9 billion years. If life on Earth could evolve in less than 4.5 billion years, why can’t it flourish in a newer and welcoming environment?
The A5 category stars that are bigger than our sun could have a planet in the “new” habitable zone for only about 200 million years because giant stars burn fast and bright. But smaller stars can remain in the red giant phase for a long period, allowing their planets to stay in the “new” Goldilocks zone for up to 9 billion years. Kaltenegger said she and her colleague Ramses M. Ramirez have submitted a second paper where they provide a list of 23 red giants within 100 light years of Earth.