Recently, researchers have closely examined a Jupiter-like exoplanet, which has persisted for billions of years after its parent star, similar to our sun, died. This planet, named WD 1856 b, is located 81 light-years from Earth in the Draco constellation. A light-year is equivalent to 9.5 trillion kilometers, the distance light covers in one year.
WD 1856 b is a gas planet, with a mass about eight times that of Jupiter, the largest planet in our solar system. Intriguingly, its atmospheric temperature is around 127 degrees Celsius, which is warmer than expected.
Having apparently moved closer to the white dwarf over time, WD 1856 b now orbits it at a distance 50 times closer than Earth is to the sun, completing a full orbit in just 1.4 days.
This scenario with WD 1856 b shows that some planets may endure even after their host stars die, similar to predictions for some planets in our solar system following the sun’s end.
However, the circumstances surrounding WD 1856 b differ from what surviving planets in our solar system might experience. The planet exists in a unique gravitational setting, as the white dwarf is part of a triple star system, including two red dwarf stars, each having about 30% of the sun’s mass.
Researchers are exploring why WD 1856 b orbits so near to the white dwarf.
“There are two main competing ideas for how WD 1856 b got into the tight orbit we observe today,” said astrophysicist Christopher O’Connor from Northwestern University in Illinois, a co-author of the study published in the journal Nature.
One theory suggests the planet was engulfed during the host star’s expansion in the red giant phase but survived near the stellar core that became the white dwarf. The other theory posits that the planet initially avoided being engulfed due to its distance from the star, later being pulled into its current orbit by gravitational influences from nearby objects like the two red dwarfs.
The original discovery of WD 1856 b, shared in 2020, provided the first concrete evidence that planets could endure the death of a sun-like star. The recent study sheds more light on the planet’s structure and history.
Using the James Webb Space Telescope, researchers found that WD 1856 b is primarily composed of hydrogen and helium, similar to Jupiter, but with an unusually high methane concentration.
The warmth of the planet is attributed to its interactions with the strong gravitational forces of the white dwarf as its orbit drew closer over time.
Stars are generally much larger than their planets, with the sun being about 1000 times the volume of Jupiter. However, WD 1856 b is 500 times larger than the white dwarf, which is only slightly bigger than Earth but significantly denser.
The white dwarf originated from a star with up to twice the mass of the sun, which died around 5 billion years ago.
THE SOLAR SYSTEM’S FATE
As the sun enters its red giant phase, it will expand to about 200 times its current size, certainly engulfing Mercury and Venus.
“The rest of the planets beyond Earth will be well beyond the sun’s maximum size, so they will most likely just continue to orbit the white dwarf left behind by the sun,” O’Connor said.
“However, because the sun will lose about half of its mass as it becomes a white dwarf, we expect the survivors to gradually drift away until they reach about double their current orbital distances,” O’Connor noted.
The future of Earth remains uncertain.
“We cannot predict Earth’s future orbit well enough to know whether it will be inside or outside the ‘danger zone’ when the sun reaches the end of its life,” O’Connor added. “Fortunately, this is one problem we still have billions of years to figure out.”
