JWST has directly imaged two giant exoplanets orbiting white dwarf stars. This discovery may reveal the fate of our solar system.

Illustration of an exoplanet around a white dwarf with a debris disk
Illustration of a cloudy exoplanet and a disk of debris orbiting a white dwarf star.
NASA / JPL-Caltech

JWST has directly imaged what appear to be two giant exoplanets in orbit around white dwarf stars. This discovery has important implications for the fate of giant planets in our solar system as the Sun evolves into a red giant and eventually becomes a white dwarf.

The Fate of Most Stars

While brilliant supernova explosions demand our attention when they burst onto the scene, the vast majority of stars will end their lives more quietly, lofting their outer layers into space and forming a glowing planetary nebula that surrounds the star’s exposed core. The core, now a white dwarf containing roughly the mass of the Sun in a sphere roughly the size of Earth, starts out extremely hot and cools slowly over billions of years.

Planetary nebula NGC 5189
A planetary nebula appears briefly during the life cycle of most stars, including those like the Sun. Planetary nebulae tend to appear round or elliptical, but they can have dramatically varied shapes, like NGC 5189 shown here.
NASA / ESA / the Hubble Heritage Team (STScI/AURA)

As stars evolve from main-sequence stars to red giants to white dwarfs, it’s clear that close-in planets will meet a fiery fate: as a red giant, the Sun will swell to more than 200 times its current radius, engulfing Mercury, Venus, and possibly Earth. But exactly how the transition affects planets watching things unfold from a distance isn’t yet clear. To learn more, we’ll need to study planets that survived the transformation, and recent observations with JWST may have revealed two planets that fit the bill.

Investigating Metal-Polluted White Dwarfs

Only a handful of planetary-mass objects have been discovered around white dwarfs, but many more are thought to exist; 25–50% of seemingly solo white dwarfs show metals in their spectra, which suggests that they’re collecting cast-off material from unseen planets or asteroids. If giant planets are common around these “metal-polluted” white dwarfs, it would suggest that 1) these planets are able to survive their home star’s red giant phase, and 2) they play a role in gravitationally nudging material toward the white dwarf.

Images of two white dwarfs with their candidate planetary companions
The two white dwarfs and their candidate planets. The object in the upper-left corner of the top row of images is a galaxy.
Mullally et al. 2024

Susan Mullally (Space Telescope Science Institute) and collaborators pointed JWST at four white dwarfs that may harbor planets. These white dwarfs have been shown to contain metals in their atmospheres and are young enough or close enough that their planets would be relatively bright. Even before carefully removing the white dwarfs’ light from the images, Mullally’s team spotted what they were looking for — a possible giant planet around two of the four white dwarfs.

Potential Planets on Outlying Orbits

The observations show a reddish object near two of the white dwarfs. If these objects are indeed planets and the same ages as their host white dwarfs (5.3 and 1.6 billion years old), they likely have masses of 1–7 and 1–2 Jupiter masses, respectively. They’re currently orbiting at estimated distances of 11.47 and 34.62 astronomical units (au), which correspond to orbital distances of 5.3 au and 9.7 au when their host stars were on the main sequence — similar to the present-day orbital distances of Jupiter and Saturn.

A comparison of the ages and orbital separations of the two new planet candidates (red triangles), the four giant planets in our solar system (blue stars), and objects with masses less than 12 Jupiter masses discovered previously through direct imaging (black circles). Click to enlarge.
Mullally et al. 2024

While the objects appear to be associated with the white dwarfs, it’s not impossible for them to instead be small photobombing objects within our solar system or distant, reddish galaxies meandering in the background. The authors pin the likelihood of their detections being a false positive at 1 in 3,000.

If future JWST observations show that these white dwarfs and their candidate planetary companions march across the sky in step, it will mark the first direct imaging detection of planets similar to the giant planets in our solar system in age, mass, and orbital distance. More than that, it will provide evidence that widely separated planets survive their host stars ballooning into red giants, and that giant planets around white dwarfs are common and help their hosts accrete metal-rich material.


“JWST Directly Images Giant Planet Candidates Around Two Metal-Polluted White Dwarf Stars,” Susan E. Mullally et al 2024 ApJL 962 L32. doi:10.3847/2041-8213/ad2348

This post originally appeared on AAS Nova, which features research highlights from the journals of the American Astronomical Society.


Image of Anthony Barreiro

Anthony Barreiro

March 5, 2024 at 6:33 pm

"They’re currently orbiting at estimated distances of 11.47 and 34.62 astronomical units (au), which correspond to orbital distances of 5.3 au and 9.7 au when their host stars were on the main sequence — similar to the present-day orbital distances of Jupiter and Saturn."

Why would these planets move away from their host stars as the stars transitioned from main sequence to white dwarf?

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Andrew James

March 6, 2024 at 2:11 am

Anthony. I think we might have to take into account the mass loss by the superwinds caused by the transition between the red giant to white dwarf. The collapse of the white dwarf by gravitation, causes an increase in temperature, then energies blow out the outer layers of the star. A simple calculation shows that 1.0 solar mass star produces a 0.6 mass white dwarf. If the gravitational pull of the star decreases, you would expect the planets would expand in their orbits.
There are other possibilities too, such as the pressure from the gas on the planetary bodies, which will increase their orbits.
The perplexing thing I find, is that you would expect the outer layers to be blown off by the superwind, so that you would expect more rocky bodies. Another thing here is that if the majority of exoplanets orbit very close to their stars, how did these two ones get so far out?

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Andrew James

March 6, 2024 at 2:33 am

NGC 5189 is in the far southern constellation of Musca. It is a bipolar nebula that looks like an 'S' in 20cm. telescopes, which is why it is called the Spiral Planetary. It's central start with much more massive than the Sun, so that it is unlikely that we can draw an analogy of the end of the life of the sun when it becomes a white dwarf. The analogy a planet surviving cannot be excluded though.
What are the most intriguing things, is that the nebulosity around the stars is in the order of about a light year. A light year compare to the size of the inner orbits of planets is minutely small. Much of the damage caused would be close to this in the region, but the outer layers far away are extremely tenuous.
There is a very good science-fiction story by Arthur C. Clarke, called 'The Songs of Distant Earth', where our planet is destroyed by an unexpected nova event. All the inner planets were destroyed, turned into cinders, where the planets glowed like incandescent lights. Clark had scientific advice on this possibility when he wrote the book. There is no reason to expect that the ashes that remain could still persist after the superwind had abated.
In my view, the future of the solar system is intriguing, especially if the planets survive, and I'm far more interested in the evolution and appearance of the planets that go through the final death throws of the stars.
Perhaps another line of study is to examine the planetary nebula gas distribution, and look for the tell-tale signs of planetary atmospheres in their wake.

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