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Explain the physical origin of the high‑speed vapor plume observed after the DART impact

Establish a physically consistent mechanism that produced the hemispherical vapor plume observed after the DART impact on Dimorphos, which expanded outward from the Didymos system at speeds up to approximately 2 km s−1 in a direction generally opposite to the DART trajectory, and characterize the conditions under which such high‑velocity, wide‑angle emission occurs.

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Background

In LICIACube images obtained after close approach, the nightside limb of Didymos appears in silhouette against a faintly illuminated background between about 172 and 183 seconds after impact. The authors suggest the most likely source is a vapor plume, supported by ground-based and Lucy spacecraft detections of a hemispherical cloud expanding away from the system.

However, while the plume’s existence and gross morphology are observed, the underlying physics driving its formation and extreme speeds remain unaccounted for, motivating a need to determine the mechanism consistent with the observed kinematics and geometry.

References

The physics of what produced this plume have not yet been fully explained, but it was observed as a hemispherical cloud expanding outward, with speeds up to ~2 km sec-1, from the Didymos system in the general direction opposite of the DART trajectory.

— High-Speed Boulders and the Debris Field in DART Ejecta (2506.16694 - Farnham et al., 20 Jun 2025) in Section 3.4 (Post-Close Approach Sky Background / Plume)