Data from NIRCam Yells at Cloud

NIRCam and MIRI coronagraphy have successfully demonstrated the ability to directly image young sub-Jupiter mass and mature gas-giant exoplanets.
However, these modes struggle to reach the sensitivities needed to find the largely unexplored populations of cold giant planets that are similar to our own Solar System's giant planets ($T_{\rm eff} = 60 - 125$\,K; $a=5 - 30$\,AU). For the first time, we explore the high-contrast imaging capabilities of MIRI imaging rather than coronagraphy. Using data from the JWST GO 6122: \textit{Cool Kids on the Block} program which targets nearby ($<6$\,pc) M-dwarfs with NIRCam coronagraphy and MIRI imaging, we demonstrate that 21\,$\mu$m MIRI imaging can detect planets with the same temperature, mass, age, and orbital separations as Saturn and Jupiter. For systems within 3\,pc, 21\,$\mu$m MIRI imaging reaches the sensitivity needed to detect planets colder than Saturn ($<95$K). NIRCam coronagraphy can achieve similar results only in the unlikely case that a cold giant planet is cloud-free. Motivated by these compelling findings, we extend our analysis to evaluate the measured performance of MIRI F2100W imaging versus NIRCam F444W coronagraphy to 70\,pc and conclude that MIRI imaging offers the advantage for systems within 20\,pc. Microlensing surveys predict an occurrence rate as high as 1-2 low-mass giant exoplanets per star, suggesting that JWST MIRI imaging surveys of nearby systems are poised to uncover a substantial population. This breakthrough enables a path towards the first direct characterization of cold giant exoplanets that are analogous to the solar system giant planets.

近红外相机（NIRCam）与中红外仪器（MIRI）的日冕成像技术已成功实现对年轻次木星质量气态巨行星及成熟气态巨系外行星的直接成像观测。然而，此类观测模式难以达到所需灵敏度，无法探测到与太阳系巨行星高度相似、尚未被广泛探索的冷态巨行星群体（有效温度$T_{
m eff}=60-125$K；轨道半长轴$a=5-30$AU）。本研究首次探索了MIRI的常规成像而非日冕成像的高对比度成像能力。依托詹姆斯·韦布空间望远镜（JWST）通用观测项目GO 6122——"Cool Kids on the Block"项目的观测数据，该项目针对距离小于6秒差距（pc）的M型矮星开展NIRCam日冕成像与MIRI成像观测，我们证实21μm波段的MIRI成像可探测到与土星、木星温度、质量、年龄及轨道间距均一致的行星。对于距离在3秒差距以内的天体系统，21μm波段MIRI成像可达到探测比土星温度更低（<95K）的行星所需的灵敏度。仅在极少数无云冷态巨行星存在的情况下，NIRCam日冕成像才能实现类似观测效果。基于上述极具说服力的发现，我们进一步扩展分析，对比评估了MIRI F2100W与NIRCam F444W日冕成像在70秒差距范围内的实测性能，得出结论：MIRI成像在距离20秒差距以内的天体系统中具备显著优势。微引力透镜巡天预测，每颗恒星周围的低质量气态巨系外行星出现率高达1-2颗，这表明针对邻近天体系统开展的JWST MIRI成像巡天有望发现大量此类行星群体。这一突破为实现首个与太阳系巨行星类似的冷态气态巨系外行星的直接表征提供了可行路径。