4,000 light-years from home, astronomers find a chilling vision of Earth’s potential future

BERKELEY, Calif. — What will happen to Earth when our Sun burns out? A newly discovered planetary system 4,000 light-years away might hold the answer, showing an Earth-like world orbiting the remnant of a star like our Sun.

Imagine Earth not as the vibrant, life-sustaining oasis we know but as a frozen, desolate world orbiting the faint ember of what was once a star like our Sun. This is the scene set by the newly discovered system, where an Earth-mass planet circles a white dwarf at a distance roughly twice that of Earth’s current orbit around the Sun. It’s a cosmic déjà vu, a preview of one possible fate awaiting our planet in the distant future.

The story of this remarkable find begins with a celestial magic trick known as gravitational microlensing. In 2020, astronomers detected a brief brightening of a distant star, magnified a thousandfold by the gravity of an intervening planetary system. This cosmic lens, dubbed KMT-2020-BLG-0414, revealed not just one but three bodies: a star about half the mass of our Sun, an Earth-sized planet, and a much larger object about 17 times the mass of Jupiter — likely a brown dwarf (a failed star).

However, the true nature of this system remained shrouded in mystery until Keming Zhang, a former doctoral student at the University of California-Berkeley, and his colleagues took a closer look using the powerful Keck II telescope in Hawaii. What they found—or rather, didn’t find—was the key to unlocking the system’s secrets. Their findings are published in the journal Nature Astronomy.

“Our conclusions are based on ruling out the alternative scenarios, since a normal star would have been easily seen,” Zhang explains in a media release. “Because the lens is both dark and low mass, we concluded that it can only be a white dwarf.”

This absence of light told a compelling story: the star at the heart of this system had already lived out its main sequence life, ballooned into a red giant, and finally settled into its current state as a white dwarf — a dense, Earth-sized stellar remnant.

The implications of this discovery ripple far beyond the boundaries of astronomy. It offers a cosmic crystal ball, showing one possible outcome for Earth as our own Sun ages. In about a billion years, our star will begin to swell, potentially engulfing the inner planets and forcing the outer ones, including Earth if it survives, into wider orbits.

“We do not currently have a consensus whether Earth could avoid being engulfed by the red giant sun in 6 billion years,” Zhang notes. “In any case, planet Earth will only be habitable for around another billion years, at which point Earth’s oceans would be vaporized by runaway greenhouse effect — long before the risk of getting swallowed by the red giant.”

While the fate of our planet remains uncertain, the KMT-2020-BLG-0414 system provides evidence that Earth-like worlds can indeed survive their stars’ tumultuous final acts. It’s a testament to the resilience of planets and a reminder of the vast timescales on which cosmic dramas unfold.

This discovery is more than just a scientific curiosity — it’s a profound reflection on our place in the universe and the ultimate fate of our cosmic home. As we gaze at the night sky, we’re not just seeing distant stars and planets; we’re seeing possible futures, cosmic postcards from billions of years hence.

As humanity contemplates its long-term future, Zhang offers a glimmer of hope, albeit a distant one. Even if Earth doesn’t survive the Sun’s red giant phase, the outer solar system might become a surprising haven.

“As the sun becomes a red giant, the habitable zone will move to around Jupiter and Saturn’s orbit, and many of these moons will become ocean planets,” he concludes. “I think, in that case, humanity could migrate out there.”