Is this white dwarf exoplanet a preview of Earth’s fate?

In about 5 billion years, our sun will start to die. But will it take Earth with it? Astronomers have spotted an exoplanet that suggests our planet might survive against the odds. EarthSky’s Will Triggs explains in this 1-minute video.

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• White dwarf stars are the small, hot cores of dead stars. A typical white dwarf forms after a star expands into a red giant, then collapses back into an object perhaps about as massive as our sun, yet only slightly bigger than the Earth.
• Planets orbiting near their stars would be consumed in the red giant phase. But it’s possible Earth could escape this fate when our sun becomes a red giant, billions of years from now.
• Astronomers discovered an Earth-sized exoplanet orbiting a white dwarf. Its survival might mean that Earth has a route for escaping being swallowed by the sun.

Earth-sized exoplanet orbiting a white dwarf star

About 5 billion years from now, astronomers believe, our sun will become a red giant star. It will consume Mercury, Venus … and probably Earth. And then the sun will collapse to become the dead, dense core of a star – a tiny white dwarf – as it dies. But the discovery of an Earth-sized planet orbiting a white dwarf 4,000 light-years away shows that our world might be able to out-run this fiery fate.

A team of astronomers, led by the University of California, Berkeley, found the planet using the W. M. Keck Observatory on Maunakea in Hawaii.

Astronomer Keming Zhang and colleagues published their peer-reviewed findings in Nature Astronomy on September 26, 2024. You can also read the free preprint on arXiv.

White dwarf exoplanet: Earth’s future?

The newly found white dwarf planet is rocky like Earth, and it’s about Earth’s size. It and its star lie some 4,000 light-years away, close to the central bulge of our galaxy. According to astronomers’ theories, this star must have swelled into a red giant, before entering this white dwarf phase.

In most scenarios, the Earth-sized planet should have been consumed and destroyed by the red giant. But it’s still there. Does that mean Earth could also escape a cataclysmic fate?

Could Earth move out to safety?

According to the researchers, there’s a chance. As our sun expands, it will also shed its mass. That means its gravitational attraction would lessen. The researchers noted that, if our sun sheds this mass quickly enough, it could have the effect of releasing Earth into a more distant orbit. And this could be the difference between being engulfed by the growing sun and remaining scorched but intact.

The researchers calculated that, in this scenario, Earth’s new orbit may be about twice the size it is now. And, interestingly, the newly-discovered planet is in an orbit about twice the size of Earth’s.

It may be a slim chance of survival, but it is possible. Earth would still no longer be habitable for life itself as we know it now, but the planet itself would still exist. Jessica Lu, associate professor and chair of astronomy at UC Berkeley wrote:

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. This system that Keming found is an example of a planet – probably an Earth-like planet originally on a similar orbit to Earth – that survived its host star’s red giant phase.

This video depicts a possible fate for Earth when the sun expands into a red giant star. If the red giant sheds its mass quickly enough to allow Earth to migrate to a wider orbit, our planet will escape being engulfed by the expanding surface of the red giant. A newly-discovered white dwarf exoplanet seems to have done exactly that. Video via Adam Makarenko/ UC Berkeley/ YouTube (Creative Commons Attribution License, reuse allowed).

Microlensing discovery

Astronomers first detected this planetary system back in 2020. They found it using the microlensing technique. That was when the white dwarf passed in front of a more distant star. The white dwarf magnified the background star’s light by 1,000 times. How does that happen? In microlensing, the gravity of the closer star acts like a lens, which focuses and amplifies the light from the more distant star.

The researchers called this particular microlensing event KMT-2020-BLG-0414. They used the Korea Microlensing Telescope Network (KMTNet) in the Southern Hemisphere to detect it, hence “KMT.”

The astronomers re-examined the system in 2023. This time, they used Keck Observatory’s second-generation Near-Infrared Camera (NIRC2), along with the adaptive optics system. This allowed them to eliminate the blur caused by Earth’s atmosphere.

Regular star or white dwarf?

If the star was a regular star, then it should have been seen in the Keck images. But the astronomers saw nothing. This led them to conclude that the star was actually a white dwarf. Zhang said:

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

Jessica Lu added:

This is a case of where seeing nothing is actually more interesting than seeing something,” said Lu, who looks for microlensing events caused by free-floating stellar-mass black holes in the Milky Way.

UC Berkeley astronomer Joshua Bloom also said:

Microlensing has turned into a very interesting way of studying other star systems that can’t be observed and detected by the conventional means, i.e. the transit method or the radial velocity method. There is a whole set of worlds that are now opening up to us through the microlensing channel, and what’s exciting is that we’re on the precipice of finding exotic configurations like this.

Bottom line: Astronomers have discovered an Earth-sized planet orbiting a white dwarf star. Does this white dwarf exoplanet mean Earth could survive the death of the sun?

Source: An Earth-mass planet and a brown dwarf in orbit around a white dwarf

Source (preprint): An Earth-Mass Planet and a Brown Dwarf in Orbit Around a White Dwarf

Via W. M. Keck Observatory

Read more: Giant planets orbiting white dwarfs: 1st images?

Read more: Solar system’s future seen: 1st planet around a white dwarf