In the distant future (about six or seven billion years from now), the Sun will begin to die and swell into a bloated red giant. Over a span of several hundred million years, it will blow away its outer layers, lose about half its mass, and leave behind its super-hot, super-dense, super-small core: a white dwarf.
The inner planets will be toast when this happens. Mercury, Venus and most likely even our precious Earth will be literally consumed by the sun and vaporized as their once benevolent host star literally invades and engulfs them. But what about the outer planets, like Jupiter and Saturn? They should survive the ordeal, being so far from the center of the solar system. However, until now there has been little direct observational evidence that such outer worlds can withstand the agony of their sun-like stellar host.
Using the James Webb Space Telescope (JWST), a team of astronomers led by Susan Mullally at the Space Telescope Science Institute targeted four white dwarfs, hoping to directly image any large planets that might still orbit them. Two turned out to be empty, but the other two show evidence of existing giant exoplanets still orbiting them. To be clear, these planets have not yet been confirmed, but if the research is successful, they will serve as a glimpse into the future of our sun and its worlds, and that future is not exactly comforting. The group’s research, which was published on the preprint server arXiv.org last month, has been accepted for publication in Letters from astrophysical journals.
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The four white dwarfs were chosen for JWST scrutiny because there seemed to be a good chance that they had possessed planets in their pre-red giant phases, and that any planets still lingering around them should be easy to see. They are relatively close to the sun in the galaxy, making the planets around them easier to detect; From very far away, the planets and host stars would merge into a single mass. Furthermore, these white dwarfs are young enough that any existing planets should still glow in the infrared due to the heat left over from their formation; That is, the younger they are, the hotter they are and the easier it is for JWST to detect them.
Most importantly, however, previous observations revealed that all four white dwarfs have surfaces contaminated with heavy elements. White dwarfs are small but massive. They are about the size of Earth, but about half the mass of the sun. This gives them a ferocious surface gravity that is 100,000 times greater than that of Earth. Any heavy elements like calcium or iron should sink quickly into your hot soup of hydrogen and helium plasma.-very quickly, even in a matter of days. If elements like that are seen, it is almost certainly because the white dwarf has recently snacked on asteroids composed of those elements. We know that in our own solar system gravitational interactions with giant planets commonly fling asteroids and comets toward the sun. If that happens in other star systems (and there’s no reason to assume it doesn’t), then seeing those heavy elements spread across the surface of a white dwarf implies the existence of large, unseen worlds farther away from the star.
JSWT is perfect for this search because in visible light, such as that primarily detected by Hubble or most ground-based telescopes, the stars are millions or even billions of times brighter than any of their planets. In infrared the contrast is lower. On top of that, white dwarfs are so hot that they emit most of their light in the ultraviolet, making them even weaker in the infrared, where they can be only a factor of a hundred times brighter than a giant planet: an easy choice. .
After astronomers processed and analyzed the images, two of the white dwarf targets, WD 1202-232 and WD 2105-82, appeared to have faint companion objects nearby. The estimated ages of these stars are 5.3 billion and 1.6 billion years, respectively. But that includes her extensive stories before entering her denouement as a white dwarf. They both made that transition between 900 and 800 million years ago, so from an astronomical point of view, they are really young.
Each of the two candidate companions has an infrared brightness consistent with that of large gas giant planets of about the same age as their host star. Its mass, deduced from its brightness at multiple wavelengths, is one to seven and one to two times the mass of Jupiter, respectively, firmly in the “planetary” mass range. This rules out the possibility that they are brown dwarfs.
Their orbital distances are very interesting. WD 1202-232’s companion candidate is about 1.8 billion kilometers from the star, and WD 2105-82’s is even further away, about 5.2 billion kilometers. However, it is highly unlikely that those remote positions are where these supposed worlds began; As stars die and lose mass, their gravitational hold on their planets weakens and, as a result, the planets migrate further away. This means they probably originated closer, about 800 million and 1.5 billion kilometers, respectively, from their stars. That’s very similar to the current distances of Jupiter and Saturn from the Sun!
If confirmed, these planets would show that the outer planets of our own solar system could very well survive the disappearance of the Sun, even if the inner planets probably will. No.
The JWST observations also support the hypothesis that giant planets fling asteroids toward their white dwarf. If no planet were found around any of the four target stars, this idea would be weakened; It would potentially imply that perhaps only the smallest planets, invisible to JWST, feed their star in this way. (I should note that such small planets could still be lurking around the other two white dwarfs where no giant planets were seen.)
But let’s not hurry too much; Again, these planets are not yet confirmed. Because of their color, astronomers were able to rule out that these objects were distant stars or objects in our own solar system. They could be very distant red background galaxies, but given the number seen in the images, the possibility of two of them apparently being so close to the white dwarfs is low. The odds are one in 3,000, according to astronomers’ calculations. This finding is not conclusive but it is hopeful.
The best way to confirm these is to conduct more observations in the near future. White dwarfs move through space and will be seen to change their position in relation to the stars in the background. If these objects are truly planets, they will move along with the stars; if they are background objects, they will appear fixed. The uncertainty is certainly frustrating right now, but time will tell.
However, given the apparent success of these observations, hopefully JWST will monitor more white dwarfs soon to see if other possible planetary survivors can be found and, with them, more information about the fate of our own solar system.
Of course, we could wait six or seven billion years to see what happens. But I’d rather know sooner, while we still have a non-vaporized planet to study it from.