NASA's asteroid impact left unexpected fingerprints months later
NASA's DART mission successfully altered an asteroid's orbit, but new analysis reveals the impact's effects persisted far longer than expected. Polarimetry data shows ejected material remained in the system months afterward, suggesting future planetary defense missions must account for extended debris dynamics that could affect follow-up observations and long-term trajectory predictions.
Originaltitel: Polarimetry of Didymos–Dimorphos: Unexpected Long-term Effects of the DART Impact
DART-missionen förändrade asteroiden Didymos-Dimorphos mer långsiktigt än tidigare antaget. Polarimetriska mätningar visar att påverkan från rymdsondens kollision skapade ett ejecta-moln vars effekter kvarstod månader senare — antingen i omloppsbana eller sedimenterad på ytan. Det ejekterade materialet består av mindre och ljusare partiklar än asteroidents ursprungliga yta, vilket framgår av förändrad albedo och grundare polarimetrikurva. Armaghs observatorium och Mullard Space Science Laboratory (UCL) övervakade systemet med polarimetrisk avbildning före och efter impakten. Gradienten i polarisering mellan asteroidens fotocenter och omgivande stoftmoln utvecklades gradvis under observationsperioden. Resultaten förbättrar förståelsen av asteroidejektas långtidsbeteende — relevant för framtida asteroidavledningsuppdrag och materialsamblandning vid högenergiimpakter.
<p>We have monitored the Didymos–Dimorphos binary system in imaging polarimetric mode before and after the impact from the Double Asteroid Redirection Test mission. A previous spectropolarimetric study showed that the impact caused a dramatic drop in polarization. Our longer-term monitoring shows that the polarization of the post-impact system remains lower than the pre-impact system even months after the impact, suggesting that some fresh ejecta material remains in the system at the time of our observations, either in orbit or settled on the surface. The slope of the post-impact polarimetric curve is shallower than that of the pre-impact system, implying an increase in albedo of the system. This suggests that the ejected material is composed of smaller and possibly brighter particles than those present on the pre-impact surface of the asteroid. Our polarimetric maps show that the dust cloud ejected immediately after the impact polarizes light in a spatially uniform manner (and at a lower level than pre-impact). Later maps exhibit a gradient in polarization between the photocentre (which probes the asteroid surface) and the surrounding cloud and tail. The polarization occasionally shows some small-scale variations, the source of which is not yet clear. The polarimetric phase curve of Didymos–Dimorphos resembles that of the S-type asteroid class.</p>