Astronomers have discovered an Earth-like planet orbiting a dead star, offering a preview of what may become of our solar system billions of years from now. Located 4,000 light-years away in the Milky Way galaxy, this distant planetary system mirrors what is predicted to happen to Earth after the sun exhausts its fuel and evolves into a white dwarf.
The system, identified by astronomers from the University of California, Berkeley, after detailed observations with the Keck Telescope in Hawaii, features a white dwarf star with about half the mass of our sun, and a planet of similar size to Earth, orbiting at roughly twice the distance of Earth’s current orbit around the sun.
A Glimpse Into Earth’s Distant Future
This discovery provides insight into a future scenario for Earth. Billions of years from now, the sun will undergo dramatic changes. It will expand into a red giant, growing larger than Earth’s current orbit, engulfing the inner planets Mercury and Venus in the process. As the sun’s mass decreases, planets will migrate outward, possibly giving Earth a chance to avoid being consumed. Eventually, the sun will shed its outer layers and leave behind a dense white dwarf, no larger than Earth but with half the mass of the original sun.
At that point, if Earth manages to survive, it will have drifted to a more distant orbit, about twice its current distance from the sun. However, life on Earth will long have ceased, as the sun’s transformation into a red giant will vaporize the planet’s oceans and make it uninhabitable.
The Significance of the Discovery
This discovery, soon to be published in Nature Astronomy, gives scientists valuable information about the life cycle of stars like the sun, from the main sequence to the red giant phase and finally to a white dwarf. The distant planetary system offers a potential glimpse into the ultimate fate of our planet.
According to Keming Zhang, the lead author of the study and a former doctoral student at UC Berkeley, “We don’t have a consensus on whether Earth will survive the red giant phase of the sun in six billion years.” Zhang, now a postdoctoral fellow at UC San Diego, also noted, “Regardless, Earth will only remain habitable for about a billion more years, as its oceans will boil away long before the sun becomes a red giant.”
While this planet orbits a white dwarf star and resides outside the habitable zone, its existence shows that planets can survive the violent transformation of their host stars. The system’s planet may have once enjoyed more habitable conditions when the star was similar to our sun.
Microlensing: A Window Into the Cosmos
The discovery of this distant system was made possible through a phenomenon called microlensing, where the gravitational pull of an object, like a star, magnifies the light from a more distant background object. In this case, the white dwarf and its planets magnified the light of a star located even farther away, bringing this fascinating system to the attention of astronomers.
In 2020, astronomers noticed a “microlensing event” when this planetary system passed in front of a distant star, brightening its light by a factor of 1,000. Dubbed KMT-2020-BLG-0414, the event was detected by the Korea Microlensing Telescope Network. Using the Keck II telescope’s adaptive optics, the team was able to confirm in 2023 that the system’s host star was indeed a white dwarf.
“We expected to see a main-sequence star, but when we detected nothing, we realized the lens must be a white dwarf,” Zhang explained. The system also contains a much larger object—likely a brown dwarf, a type of “failed star” with a mass too low to sustain fusion.
A Path to Future Discoveries
This study highlights the value of microlensing in discovering exoplanets and their host stars, many of which are too faint to be detected by more conventional methods. The detection of KMT-2020-BLG-0414 is part of a broader effort to study these rare events and learn more about how planetary systems evolve after their stars die.
“We are at the beginning stages of discovering other exotic star-planet configurations using microlensing,” said Joshua Bloom, a UC Berkeley professor and co-author of the study. “There’s a whole new set of worlds opening up to us.”
As humanity looks to the future, this discovery offers both hope and a cautionary tale. While Earth may face a similar fate billions of years from now, planets surviving the death of their stars, even under harsh conditions, provide a glimmer of possibility for survival in the distant reaches of space. In the meantime, missions like NASA’s Nancy Grace Roman Telescope, set to launch in 2027, will continue to help uncover more planets around stars that have long since perished.
In an ironic twist, as our sun transforms into a red giant, the habitable zone of the solar system will shift outward to the moons of the gas giants, like Europa and Ganymede around Jupiter or Enceladus around Saturn. These frozen moons, which likely harbor subsurface oceans, may become viable homes for life as the sun swells and heats them.
While Earth’s future remains uncertain, one thing is clear: the cosmos holds many surprises and potential paths for planetary survival long after the death of a star.