一个国际天文学家团队利用NASA/ESA/CSA James Webb太空望远镜观测了木星大小的系外行星WD 1856 b凌越其宿主白矮星的过程，成功量测了该行星的质量、温度，并首次侦测到环绕已死亡恒星运行之行星的大气层。WD 1856 b于2020年由NASA的TESS卫星与Spitzer太空望远镜发现，距地球约80光年（约25.7秒差距），环绕白矮星WD 1856+534运行，轨道周期仅34小时，轨道距离不到300万公里（约186万英里），比地球与太阳的距离近50倍。该行星体积约与木星相当，但其宿主白矮星仅地球大小，使得行星体积为恒星的7倍。首席作者为英国University of St. Andrews的Ryan MacDonald。

Webb的凌日观测揭示了该行星质量介于木星质量的4至11倍之间。研究团队透过比较凌日期间不同波长的光度下降差异，发现红外光的减弱幅度较小，其差值来自行星自身热辐射，由此推算出行星表面温度约为摄氏126度（约华氏259度），显著高于仅靠白矮星光照所能达到的温度。美国Northwestern University的共同作者Christopher O'Connor利用亚恒星天体的冷却模型，结合Webb所测得的质量与温度数据，将行星温度回溯至过去，推断加热事件最可能发生在恒星演变为白矮星后的30亿至55亿年之间。此结果支持行星原先位于远离恒星的宽轨道上，在红巨星阶段幸免于难，之后才在三星系统中外部伴星的引力扰动下向内迁移。该研究成果于2026年7月1日发表于《Nature》期刊。

大气侦测方面，美国Cornell University的共同作者Victoria Boehm指出，团队发现了细小云粒子与碳氢化合物（最可能为甲烷）的特征讯号，这是首次在凌越已死亡恒星的行星上观测到大气成分。团队已利用Webb再进行四次WD 1856 b的凌日观测，以深入研究其大气化学组成。这项研究为太阳系的遥远未来提供了前瞻性视角：约50亿年后，太阳将膨胀为红巨星，体积扩大逾100倍，随后演变为白矮星，届时水星、金星乃至地球可能被吞噬，而外层气态巨行星的命运仍不确定。MacDonald表示，这是科学家首次能够前瞻性地观察类太阳恒星残骸周围外行星的可能未来，如同使用时间机器窥探太阳系的远景。

An international team used the NASA/ESA/CSA James Webb Space Telescope to observe the Jupiter-sized exoplanet WD 1856 b transiting its white dwarf host star, measuring the planet's mass and temperature and detecting its atmosphere for the first time around a dead star. Discovered in 2020 by NASA's TESS and the Spitzer Space Telescope, WD 1856 b orbits white dwarf WD 1856+534 approximately 80 light-years from Earth with a period of just 34 hours at a separation of less than 3 million kilometres (approximately 1.86 million miles), 50 times closer than Earth orbits the Sun. The planet is roughly Jupiter-sized, yet its host white dwarf is only Earth-sized, making the planet seven times larger than its star. Lead author Ryan MacDonald is based at the University of St. Andrews in the United Kingdom.

Webb's transit observations revealed that the planet's mass lies between four and eleven Jupiter masses. By comparing the dimming across wavelengths during transit, the team found less reduction in infrared light, with the difference attributable to the planet's own thermal emission, yielding a temperature of approximately 126 degrees Celsius (roughly 259 degrees Fahrenheit)—significantly hotter than white dwarf irradiation alone could explain. Co-author Christopher O'Connor of Northwestern University applied sub-stellar cooling models combined with Webb's mass and temperature data to trace the planet's thermal history backward, concluding that the heating event most likely occurred between 3 and 5.5 billion years after the star became a white dwarf. This supports a scenario in which the planet occupied a wide, safe orbit during the destructive red giant phase and migrated inward later under gravitational perturbation from companion stars in the triple star system. The results were published on 1 July 2026 in Nature.

Regarding atmospheric detection, co-author Victoria Boehm of Cornell University reported signatures of small cloud particles and hydrocarbons, most likely methane, marking the first atmospheric detection on a planet transiting a dead star. The team has conducted four additional Webb transits of WD 1856 b to further probe its atmospheric chemistry. The study offers a forward-looking perspective on the Solar System's distant future: in approximately five billion years the Sun will swell into a red giant exceeding 100 times its current size before collapsing into a white dwarf, likely destroying Mercury, Venus, and possibly Earth, while the fate of the outer gas giants remains uncertain. MacDonald noted this is the first time scientists have been able to look forward to what might happen to outer planets around the remnant of a Sun-like star, likening the discovery to using a time machine to peer into the Solar System's distant future.