Solar system’s future seen: 1st planet around a white dwarf
Scientists now have evidence that some of our solar system’s planets can survive the death of our sun. They said on October 13, 2021, that they’ve found a star system – about 6,500 light-years away, toward the center of our Milky Way galaxy – consisting of a star once like our sun but now a compact white dwarf. This star has a gas giant planet still orbiting it, similar in size and orbit to our solar system’s large planet Jupiter. It’s evidence that Jupiter (at least) can and will survive when our own sun swells up to become a red giant, just before it enters the white dwarf stage of star evolution. The newly discovered Jupiter-sized planet now circles its star’s cold, burnt-out remains. And so, for the first time, we’re glimpsing into our own solar system’s future, some 5 billion years from now.
This evidence confirms that planets orbiting at a large enough distance can continue to exist after their star’s death. Given that this system is an analog to our own solar system, it suggests that Jupiter and Saturn might survive the sun’s red giant phase, when it runs out of nuclear fuel and self-destructs.
Solar system’s future: outer planets vs. inner planets
Scientists have long wondered if the outer planets would be safe from the star’s bloated red giant phase and would stick around for the long haul. Now they have evidence that they will. But Earth’s prospects of existing past the red giant phase may be bleak. When the sun expands into a red giant, scientists expect it to swallow Mercury, Venus and perhaps Earth as well. Therefore, humankind will need an evacuation plan to survive. Co-author David Bennett of the University of Maryland and NASA’s Goddard Space Flight Center said:
Earth’s future may not be so rosy because it is much closer to the sun. If humankind wanted to move to a moon of Jupiter or Saturn before the sun fried the Earth during its red supergiant phase, we’d still remain in orbit around the sun, although we would not be able to rely on heat from the sun as a white dwarf for very long.
Making the discovery
The sun is a main sequence star. Main sequence stars are average stars that, as they age, burn through their hydrogen and begin to expand into red giants. It is the red giant phase that may eat Earth alive, depending on how large it gets before the sun collapses in on itself and puffs off its outer layers. Then the sun settles into the remainder of its existence as a cooling white dwarf. A white dwarf is, essentially, a dead star.
A white dwarf is about the size of Earth with a mass about half that of the sun. Due to their small size and cool temperatures, they’re dim and difficult to detect. The Keck telescope used high-resolution near-infrared imaging to spot this white dwarf and planet. Gravitational microlensing revealed the pair. Gravitational microlensing is when a nearby star aligns with a distant star. The closer star acts like a lens, magnifying the light from the farther star.
The scientists noticed a warping of light from the lensed star, and that’s what led to the discovery of the exoplanet. The white dwarf is about 60% the mass of our sun. Its exoplanet is about 40% more massive than Jupiter. Due to its dimness, scientists ruled out that the light of this star was from a main sequence star or a brown dwarf. Co-author Jean-Philippe Beaulieu of the University of Tasmania explained:
We have also been able to rule out the possibility of a neutron star or a black hole host. This means that the planet is orbiting a dead star, a white dwarf. It offers a glimpse into what our solar system will look like after the disappearance of the Earth, whipped out in the cataclysmic demise of our sun.
The scientists are using their new data to help discover how many other planets have survived and are in orbit around white dwarfs. The Nancy Grace Roman Telescope, set to launch in the middle of this decade, will be able to directly image giant planets. The Roman Space Telescope should be able to survey planets orbiting white dwarfs as far away as the galactic bulge. John O’Meara of Keck Observatory summed up with:
This is an extremely exciting result. It’s wonderful to see today an example of the kind of science Keck will be doing en masse when Roman begins its mission.
Bottom line: Scientists got a peek at the solar system’s future when they found a gas giant planet orbiting a white dwarf. One day our sun will expand into a red giant and then shrink into a white dwarf, where it will spend the rest of its days.