While the poet Robert Frost wrote that “Some say the world will end in fire/ Some say in ice,” earthlings may take cold comfort from a newly published discovery that suggests the latter is more likely than previously believed.
Astronomers using the W. M. Keck Observatory on Maunakea discovered a planet roughly 4,000 light years away that offers a glimpse of Earth’s possible future. The planet has roughly the same mass as Earth, but orbits a white dwarf star, the cool core of a dead star that was once much like our sun.
Jim Lyke, staff astronomer at Keck, said the unnamed planet is orbiting its star about twice as far away as Earth does the sun. Compared to our solar system, the planet would be a little bit beyond the orbit of Mars, outside the habitable zone of our solar system and well outside any habitable zone for a white dwarf.
“The concept is that, as a star sheds its outer layers as it becomes a red giant, it becomes less massive, with a reduced gravity, and the planet pulls away from it,” Lyke said.
Planets of this sort are not unheard of, but are very rare, Lyke said. For one thing, the small size and faintness of white dwarf stars makes them difficult to detect.
This star, he said, was discovered through “microlensing,” a phenomenon when a celestial object too faint to be visible passes in front of a star that is visible. When that happens, the gravity of the nearer object acts as a lens for the light of the more distant star, causing a detectable fluctuation that astronomers can use to infer the character of the occluding object.
Another reason these planets are hard to find is because of the simple reason that white dwarf stars were previously red giant stars, which likely would have engulfed and destroyed any nearby planets.
Indeed, when the sun begins to die — estimated to be in as few as 1 billion years — it will become a red giant and expand to hundreds of times its size. This will certainly engulf Mercury and Venus, and quite possibly Earth as well — unless it manages to escape in time.
“The rocky body of Earth could survive,” Lyke said. “Of course, it would be very different. There would be no oceans, no atmosphere. It would be a rock.”
Lyke said there is no current consensus on which fate awaits Earth, although statistics favor fire, as the study notes there’s likely only a slim chance for a planet to escape the red giant. But the question is academic, as Lyke added that “fortunately, none of us will be around to find out.”
Lead author of the study, Keming Zhang, said in a statement that all life on Earth likely will end when the runaway greenhouse effect caused by the expanding sun causes the oceans to vaporize, long before the planet either gets incinerated or flung into the frozen void.
Zhang noted that the end of Earth does not necessarily have to mean the end of humans, who could find refuge on some of the larger moons of Jupiter and Saturn, which could warm to habitable levels as the sun expands.
But in 8 billion years when the sun finally collapses into a white dwarf, those moons will end in ice all the same.
Email Michael Brestovansky at mbrestovansky@hawaiitribune-herald.com.