A team of astronomers has uncovered an Earth-like planet orbiting a star located 4,000 light years away from the solar system, potentially offering insights into Earth's distant future. The rocky planet, about the same mass as Earth, revolves around a white dwarf in the constellation Sagittarius.
The discovery brings a glimmer of hope for Earth's survival when our sun enters its final stages. It suggests that Earth could potentially avoid being consumed by the expanding sun, opening up possibilities for human migration to the outer solar system, with moons such as Europa, Callisto, and Ganymede around Jupiter, or Enceladus near Saturn, becoming possible havens for future generations.
What is a white dwarf?
A white dwarf is a star's remnant after it has run out of nuclear fuel and shed its outer layers. It symbolises the sun's eventual fate. The sun will grow into a red giant as its nuclear fuel runs out, then shrink to become a white dwarf. The extent of its expansion will determine which planets in the solar system will be engulfed - Mercury and Venus are likely to be consumed. But what about Earth?
In a study published in Nature Astronomy, researchers from the University of California, Berkeley, used the Keck Telescope in Hawaii to observe a system designated KMT-2020-BLG-0414. The system contains a white dwarf star with an Earth-sized planet in an orbit twice as far from the star as Earth is from the sun. Alongside the planet is a brown dwarf - a planet roughly 17 times the mass of Jupiter.
This finding supports the theory that as the sun expands into a red giant, its loss of mass will push the planets into more distant orbits. This phenomenon could allow Earth to escape destruction. Jessica Lu, an associate professor of astronomy at UC Berkeley, noted, "Whether life can survive on Earth through that (red giant) period is unknown. But certainly, the most important thing is that Earth isn't swallowed by the Sun when it becomes a red giant."
Future of Earth
"We do not currently have a consensus whether Earth could avoid being engulfed by the red giant sun in six billion years," said Keming Zhang, the lead author and a former doctoral student at the UC Berkeley, who is now an Eric and Wendy Schmidt AI in Science Postdoctoral fellow at UC San Diego.
"In any case, planet Earth will only be habitable for another billion years, at which point Earth's oceans would be vaporized by the runaway greenhouse effect-long before the risk of getting swallowed by the red giant."
Could humanity find refuge beyond Earth? As the sun swells into a red giant, the habitable zone in the solar system will shift outward to the orbits of Jupiter and Saturn. Many of their moons, such as Europa and Callisto, could become ocean worlds capable of supporting life. Zhang suggested, "Humanity could migrate out there."
