Free Astronomy Magazine September-October 2026

50 SEPTEMBER-OCTOBER 2026 ASTRO PUBLISHING N ASA’s James Webb Space Telescope measured the constituents of exoplanet WD 1856 b as it passed in front of its star, finding signs of methane. WD 1856 b orbits a white dwarf star the size of Earth. As a result, the planet blocks more than half of the star’s light. The red bands indicate where bumps in the spectrum show that this planet’s atmosphere contains methane. [NASA, ESA, CSA, Joseph Olmsted (STScI)] is key to determining whether the heating was from being engulfed by the red giant or occurred during an inward migration They concluded that the heating most likely happened between 3 and 5.5 billion years after the star became a white dwarf. In this sce- nario, the planet was on a wide orbit that kept it safe from the star during its destructive red giant phase, and only migrated to its pres- ent location later on. “As the planet moved inward, its interactions with the strong gravity of the white dwarf will have caused it to warm up considerably, and it has been cooling ever since,” said O’Connor. Light from the star passing through the planet’s atmosphere also picked up information about its chemical composition. “We saw the telltale signatures of small cloud particles and hydrocarbons, most likely meth- ane, which is the first time we have seen an atmosphere on a planet transiting a dead star,” said co-au- thor Victoria Boehm of Cornell Uni- versity. “We recently observed four more transits of WD 1856 b with Webb to take a deeper look into its atmospheric chemistry and can’t wait to see the results.” In approximately five billion years, the Sun will run out of hydrogen fuel in its core and swell up more than 100 times larger than it is now into a red giant star. It will then shed its outer layers and end its life as a white dwarf star. Mercury, Venus, and possibly the Earth will be de- stroyed by the red giant. However, the fate of the more distant planets, particularly the gas giants, is unclear. Finding and studying planets in orbit around the remnants of Sun-like stars after their death is a means of learning what might happen in our own solar system in the far future. “We’re used to looking back in time when we use telescopes, but this is the first time we have been able to look forward to what might happen to the outer planets around the remnant of a Sun-like star,” said MacDonald. “It’s like using a time machine to peer into the distant fu- ture of our solar system.” !