Ejecta Evolution Following a Planned Impact into an Asteroid: The First Five Weeks

The impact of the DART spacecraft into Dimorphos, moon of the asteroid Didymos, changed Dimorphos' orbit substantially, largely from the ejection of material. We present results from twelve Earth-based facilities involved in a world-wide campaign to monitor the brightness and morphology of the ejecta in the first 35 days after impact. After an initial brightening of ~1.4 magnitudes, we find consistent dimming rates of 0.11-0.12 magnitudes/day in the first week, and 0.08-0.09 magnitudes/day over the entire study period. The system returned to its pre-impact brightness 24.3-25.3 days after impact through the primary ejecta tail remained. The dimming paused briefly eight days after impact, near in time to the appearance of the second tail. This was likely due to a secondary release of material after re-impact of a boulder released in the initial impact, through movement of the primary ejecta through the aperture likely played a role.Comment: 16 pages, 5 Figures, accepted in the Astrophysical Journal Letters (ApJL) on October 16, 202

Ejecta Evolution Following a Planned Impact into an Asteroid: The First Five Weeks

The impact of the Double Asteroid Redirection Test spacecraft into Dimorphos, moon of the asteroid Didymos, changed Dimorphos’s orbit substantially, largely from the ejection of material. We present results from 12 Earth-based facilities involved in a world-wide campaign to monitor the brightness and morphology of the ejecta in the first 35 days after impact. After an initial brightening of ∼1.4 mag, we find consistent dimming rates of 0.11–0.12 mag day−1 in the first week, and 0.08–0.09 mag day−1 over the entire study period. The system returned to its pre-impact brightness 24.3–25.3 days after impact though the primary ejecta tail remained. The dimming paused briefly eight days after impact, near in time to the appearance of the second tail. This was likely due to a secondary release of material after re-impact of a boulder released in the initial impact, though movement of the primary ejecta through the aperture likely played a role

Observational Evidence for Summer Rainfall at Titan's North Pole

International audienceMethane rain on Saturn's moon Titan makes it the only place, other than Earth, where rain interacts with the surface. When and where that rain wets the surface changes seasonally in ways that remain poorly understood. Here we report the discovery of a bright ephemeral feature covering an area of 120,000 km 2 near Titan's north pole in observations from Cassini's near-infrared instrument, Visual and Infrared Mapping Spectrometer on 7 June 2016. Based on the overall brightness, spectral characteristics, and geologic context, we attribute this new feature to specular reflections from a rain-wetted solid surface like those off of a sunlit wet sidewalk. The reported observation is the first documented rainfall event at Titan's north pole and heralds the arrival of the northern summer (through climatic evidence), which has been delayed relative to model predictions. This detection helps constrain Titan's seasonal change and shows that the "wet-sidewalk effect can be used to identify other rain events." Plain Language Summary Cassini arrived in the Saturnian system in the southern summers of 2004. As expected, the Cassini team observed cloud cover, storms, and precipitation on the south pole. Like Earth, Titan has an axial tilt (27 •) and its seasons vary over its year (30 Earth years). Ever since this shift in season began, the Cassini team eagerly waited for observations indicating cloud cover and precipitation that went missing from the northern latitudes. Our rainfall observation at the north pole is a major finding for two important reasons. First, this discovery observation heralds the much awaited arrival of the north polar summer rainstorms on Titan. This atmospheric phenomenon has been delayed compared to the theoretical predictions and was perplexing Titan researchers and climate modelers especially because the north pole hosts most of Titan's lakes and seas. Second, it is extremely difficult to detect rainfall events on Titan due to its thick atmospheric haze and very limited opportunities to view the surface (and its changes). We have used a novel phenomenon-the smoothening of a previously dry, rough surface by a thin layer of fluid after rainfall, similar to a wet sidewalk-as evidence for rainfall events on the surface of Titan

Observational Evidence for Summer Rainfall at Titan's North Pole

International audienc

Ejecta Evolution Following a Planned Impact into an Asteroid:The First Five Weeks

The impact of the DART spacecraft into Dimorphos, moon of the asteroid Didymos, changed Dimorphos' orbit substantially, largely from the ejection of material. We present results from twelve Earth-based facilities involved in a world-wide campaign to monitor the brightness and morphology of the ejecta in the first 35 days after impact. After an initial brightening of ~1.4 magnitudes, we find consistent dimming rates of 0.11-0.12 magnitudes/day in the first week, and 0.08-0.09 magnitudes/day over the entire study period. The system returned to its pre-impact brightness 24.3-25.3 days after impact through the primary ejecta tail remained. The dimming paused briefly eight days after impact, near in time to the appearance of the second tail. This was likely due to a secondary release of material after re-impact of a boulder released in the initial impact, through movement of the primary ejecta through the aperture likely played a role