How a planet survived the death of its sunlike star
Someday, several billion years from now, our sun will expand into the last phase of its life when it becomes a red giant. When it does, it will engulf most of the inner planets in its swollen atmosphere. Eventually, all that will be left of the sun is its dense core. That’s when it will reach the end stage of its evolution, as a white dwarf star.
Will Earth survive? That’s still a matter of debate. But on July 1, 2026, NASA said the James Webb Space Telescope (JWST) investigated a gas giant planet that not only survived the death of its sunlike star, but is also 50 times closer to its star than Earth is to the sun.
The planet in question (or exoplanet, as we call it when it orbits a star other than the sun) is named WD 1856 b, and it’s orbiting a white dwarf star. When the star was a red giant, it should have destroyed any nearby planet. But this gas giant exoplanet still orbits its star once every 34 hours from less than 2 million miles (3 million km or 0.02 astronomical units) away.
The researchers published their peer-reviewed study in the journal Nature on July 1, 2026.
Investigating this mysterious planet
To find out how a planet so close to its star could have survived the star’s red giant phase, a team of astronomers turned Webb on it. From the telescope’s point of view, the planet passes right in front of the star in what’s called a transit. During a transit, astronomers can get a look at the planet’s atmosphere. The team looked at what the atmosphere was composed of and measured its temperature.
Despite its star having cooled into a white dwarf stage, the planet itself was warmer than astronomers expected. They determined the planet’s atmosphere was a toasty 260 degrees Fahrenheit (126 C). That’s hotter than it would be if the star was the sole source of heat.
The team also managed to discern a bit of the planetary atmosphere’s chemical composition. Co-author Victoria Boehm of Cornell University said:
We saw the telltale signatures of small cloud particles and hydrocarbons, most likely methane, which is the first time we have seen an atmosphere on a planet transiting a dead star.
NASA’s Transiting Exoplanet Survey Satellite originally discovered the planet orbiting the star in 2020. The pair are 80 light-years away. Interestingly, now that the star is in its white dwarf phase, the planet is much larger than the star. Lead author Ryan MacDonald of the University of St. Andrews in the United Kingdom said:
The planet is about the size of Jupiter, but the white dwarf it orbits is the size of Earth, so the planet is seven times larger than its star.
So how did this close planet survive?
The planet is simply too close to its star to have survived there during the red giant phase. So astronomers reasoned that it migrated into that position sometime after the red giant phase ended. Looking closer at the temperature of the planet helped them crack the case.
The white dwarf doesn’t provide enough heat to account for the temperature of the planet. So there must be internal heat in the planet from an earlier time. Co-author Christopher O’Connor of Northwestern University modeled the heat of the planet backward to determine how long it took the planet to cool down. This would help astronomers know how long ago the planet acquired its heat. What they really wanted to know is if the planet heated up due to the red giant phase of its star or as a consequence of its journey closer to the star.
And the calculations showed the planet heated up between 3 and 5.5 billion years after the star became a white dwarf. So the heating couldn’t have been from the red giant phase. Originally, the scientists said, the planet was far enough away from the star in its orbit that it didn’t heat up as the stellar atmosphere swelled. But, O’Connor said:
As the planet moved inward, its interactions with the strong gravity of the white dwarf will have caused it to warm up considerably, and it has been cooling ever since.
What’s next for the surviving planet?
The exoplanet WD 1856 b will continue to slowly cool over the next few billion years. If there were any form of life on the planet, there’s no telling how it fared during the wild ride inward toward its star and the subsequent increase in heat to the point where it is cooling today.
Perhaps the future of Jupiter or one of the other gas giant planets in our solar system will resemble that of WD 1856 b. MacDonald said:
We’re used to looking back in time when we use telescopes, but this is the first time we have been able to look forward to what might happen to the outer planets around the remnant of a sunlike star. It’s like using a time machine to peer into the distant future of our solar system.
Bottom line: Scientists have solved the mystery of how a planet survived the death of its star. The planet is 50 times closer to its star than Earth is to the sun. So how did it survive the star’s red giant phase?
Source: Aerosols and hydrocarbons in the atmosphere of a white dwarf planet
Via NASA