by The James Webb Space Telescope (JWST) has already proven adept at looking into the past by imaging distant objects, but new ones could see the powerful instrument acting almost like a ball scientific crystal, staring into the distance of the future. Solar system.
The JWST carried out its prognosis when it made a rare direct possible direction of two extrasolar planets, or “exoplanets,” orbiting two different dead stars, or “white dwarfs.”
Not only do the planets strongly resemble the solar system’s gas giants Jupiter and Saturn, but the white dwarfs also serve as analogs to the fate of the sun. When the sun transforms into a white dwarf itself, the change is likely to destroy the planets of the inner solar system – all the way out to Jupiter.
“Very few planets have been discovered in white dwarf stars. What is unusual about these two candidate planets is that they are more similar to planets in our outer solar system in temperature, age, mass and orbital separation than any previously found planets this,” Susan. Mullaly, lead author of the research, which has yet to be peer-reviewed, and an astronomer at the Space Telescope Science Institute, told Space.com. “This gives us our first chance to see what a planetary system looks like after the death of its star.”
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A glimpse of our future
The planet candidates were directly observed by JWST’s Mid-Infrared Instrument (MIRI) orbiting the white dwarfs WD 1202-232 and WD 2105-82. One exoplanet candidate lies at a distance from its white dwarf host that is equivalent to about 11.5 times the distance between Earth and the sun. The other candidate sits further from its dead parent star, at a distance of about 34.5 times the separation between our planet and our star.
The masses of the planets are currently uncertain, and Mullaly and colleagues estimate that they are between 1 and 7 times that of Jupiter, the most massive planet in the solar system.
When the sun exhausts its fuel supply for the nuclear fusion processes at its core in about 5 billion years, it will emerge as a red giant. Nuclear fusion, however, will continue in its outer layers. This reaches those outer layers of our star as far as Mars, engulfing Mercury, Venus, Earth, and possibly, the Red Planet itself. Eventually, these outer layers will cool, leaving the star’s smoldering core, now a white dwarf, surrounded by a planetary nebula of depleted stellar material.
However, these exoplanet detections suggest what would happen to the planets beyond Mars, the gas giants Jupiter and Saturn, when the sun dies.
“Our sun is expected to become a white dwarf star in 5 billion years,” Mullaly said. “We expect planets to drift out, into wider orbits, after a star dies. So, if you were to turn back the clock on these candidate planets, you would expect them to have similar orbital separations with Jupiter and Saturn.
“If we can confirm these planets, they will provide direct evidence that planets like Jupiter and Saturn can survive the death of their host stars.”
In addition, the white dwarfs at the heart of this discovery are contaminated with elements heavier than hydrogen and helium, which astronomers call “metals”. This could hint at what will happen to the bodies in the asteroid belt between Mars and Jupiter after the sun dies.
“We suspect that the giant planets cause metal pollution by driving comets and asteroids onto the surface of the stars,” explained Mullaly. “These planets strengthen the link between the metal pollution and the planets. Since 25% to 50% of the white dwarfs show this type of pollution, it means that giant planets are common around white dwarf stars.”
Therefore, Jupiter and Saturn could find any asteroids that survived the death of the sun for their bodies.
The double discovery is impressive beyond what it predicts for the future of our planetary system — it represents a rare scientific achievement.
Just a rare exoplanet detection
Since the discovery of the first exoplanets in the mid-1990s, astronomers have found about 5,000 life orbiting outside the solar system. According to the Planetary Society, as of April 2020, only 50 of these exoplanets have been discovered with direct imaging.
That’s because any light from such a massive planet is usually overwhelmed by the intense light from that planet’s parent star, making an exoplanet look exactly like seeing a firefly sitting on a lighthouse’s light bulb .
As a result, exoplanets are usually seen with the effect they have on starlight, by reducing light output as they transit, or by “transiting,” the face of the star, or by a “wobble” motion created as the planet tugs gravitationally on the star.
“We imaged these two exoplanets directly, which means we took their picture and we see the light produced by the planet itself,” Mullaly said. “Most of the exoplanets discovered have been found using the transit method or by measuring the motion of the star. These indirect methods tend to favor planets much closer to the star. Direct imaging is better to find planets further away from the star, at wider orbital separations.”
She explained that by seeing these planets directly, the JWST can further study these worlds; now scientists can begin to investigate things like the composition of the planets’ atmospheres and directly measure their masses and temperatures.
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Mullaly said that everything she and her team discovered about these exoplanets was unexpected, and that these mysteries could change the way astronomers think about exoplanets like this in general.
Alternatively, the strange features of the targeted worlds may provide subtle clues to long-sought migrations.
“If these are planets, then surprisingly they are not as red in the mid-infrared as we might expect. The amount of light collected by JWST at 5 and 7 microns is brighter than might we expect for the two exoplanet candidates given their age and how bright they are at 15 microns,” concluded Mullaly. “This could challenge our understanding of physics and chemistry of exoplanet atmospheres.
“Or maybe it means there’s another light source, like a heated moon orbiting the planet.”
The team’s research is available as a preprint on the arXiv research repository site.
