近日，荷兰莱顿大学的Matthew Kenworthy及其研究小组与美国俄亥俄州立大学的Michael Rizzo Smith以及法国南方光谱项目观测队合作并取得一项新进展。经过不懈努力，他们揭示行星碰撞的余辉和由此产生的碎片云的凌日现象。相关研究成果已于2023年10月11日在国际权威学术期刊《自然》上发表。

该研究团队对年轻的（约3亿年前）类太阳恒星ASASSN-21qj进行了综合观测。观测结果显示，红外增亮与黑体温度1000开尔文一致，且恒星的光度在持续约1000天内增加了4%。此外，在持续约500天的时间里，出现了复杂而深度的、波长依赖的光学日食。日食在红外增亮后的2.5年开始，暗示其轨道周期至少为2.5年。这些观测结果与两颗质量为地球数倍至数十倍的系外行星在距中心恒星2-16个天文单位处发生碰撞相符。碰撞产生了一个热且高度延伸的撞击后遗迹，其亮度足以解释红外观测结果。撞击碎片的凌日形成了一个长云带，由于轨道运动，导致了随后复杂的主星日食。

据悉，已知行星在由尘埃和气体构成的旋转圆盘中生长，这些圆盘围绕恒星形成。部分恒星会在气体成分从圆盘中移除后经历巨大的碰撞。热斯皮策任务的监测计划已记录了几颗恒星红外输出的快速变化，这些变化解释为行星尺度碰撞导致的温暖尘埃物质表面积变化，随后被中心恒星加热。具体例子包括NGC 2354-ID8、HD 166191和V488 Persei。

附：英文原文

Title: A planetary collision afterglow and transit of the resultant debris cloud

Author: Kenworthy, Matthew, Lock, Simon, Kennedy, Grant, van Capelleveen, Richelle, Mamajek, Eric, Carone, Ludmila, Hambsch, Franz-Josef, Masiero, Joseph, Mainzer, Amy, Kirkpatrick, J. Davy, Gomez, Edward, Leinhardt, Zo, Dou, Jingyao, Tanna, Pavan, Sainio, Arttu, Barker, Hamish, Charbonnel, Stphane, Garde, Olivier, Le D, Pascal, Mulato, Lionel, Petit, Thomas, Rizzo Smith, Michael

Issue&Volume: 2023-10-11

Abstract: Planets grow in rotating disks of dust and gas around forming stars, some of which can subsequently collide in giant impacts after the gas component is removed from the disk. Monitoring programmes with the warm Spitzer mission have recorded substantial and rapid changes in mid-infrared output for several stars, interpreted as variations in the surface area of warm, dusty material ejected by planetary-scale collisions and heated by the central star: for example, NGC 2354–ID8 , HD 166191 and V488 Persei. Here we report combined observations of the young (about 300million years old), solar-like star ASASSN-21qj: an infrared brightening consistent with a blackbody temperature of 1,000 Kelvin and a luminosity that is 4 percent that of the star lasting for about 1,000 days, partially overlapping in time with a complex and deep, wavelength-dependent optical eclipse that lasted for about 500days. The optical eclipse started 2.5 years after the infrared brightening, implying an orbital period of at least that duration. These observations are consistent with a collision between two exoplanets of several to tens of Earth masses at 2–16 astronomical units from the central star. Such an impact produces a hot, highly extended post-impact remnant with sufficient luminosity to explain the infrared observations. Transit of the impact debris, sheared by orbital motion into a long cloud, causes the subsequent complex eclipse of the host star.

DOI: 10.1038/s41586-023-06573-9

Source: https://www.nature.com/articles/s41586-023-06573-9