Successful kinetic impact into an asteroid for planetary defence

Abstract

Although no known asteroid poses a threat to Earth for at least the next century, the catalogue of near-Earth asteroids is incomplete for objects whose impacts would produce regional devastation1,2. Several approaches have been proposed to potentially prevent an asteroid impact with Earth by deflecting or disrupting an asteroid1–3. A test of kinetic impact technology was identified as the highest-priority space mission related to asteroid mitigation1. NASA’s Double Asteroid Redirection Test (DART) mission is a full-scale test of kinetic impact technology. The mission’s target asteroid was Dimorphos, the secondary member of the S-type binary near-Earth asteroid (65803) Didymos. This binary asteroid system was chosen to enable ground-based telescopes to quantify the asteroid deflection caused by the impact of the DART spacecraft4. Although past missions have utilized impactors to investigate the properties of small bodies5,6, those earlier missions were not intended to deflect their targets and did not achieve measurable deflections. Here we report the DART spacecraft’s autonomous kinetic impact into Dimorphos and reconstruct the impact event, including the timeline leading to impact, the location and nature of the DART impact site, and the size and shape of Dimorphos. The successful impact of the DART spacecraft with Dimorphos and the resulting change in the orbit of Dimorphos7 demonstrates that kinetic impactor technology is a viable technique to potentially defend Earth if necessary.

Lifted particles from the fast spinning primary of the Near-Earth Asteroid (65803) Didymos

“…𝑎 𝑐 ∕𝑔 is the driving magnitude here (rather than density), where 𝜔 is the spin rate and 𝑟 𝑒𝑞 is the equatorial radius of Didymos. The nominal values from Daly et al (2023) give 𝑎 𝑐 ∕𝑔 = 1.235, which is very close to the (𝑀 1 , 𝑉 4 ) set, providing more mass in orbit than our nominal case. 𝑎 𝑐 ∕𝑔 = 1 for 𝑟 ′ 𝑒𝑞 = 396 m, which is the minimum distance from the spin axis at which lift-off is possible, some 30 m smaller than the estimated equatorial radius extent.…”

“…Available data do not allow predictions about the internal structure of any of the two bodies. Nevertheless, updated estimates of some physical parameters critical to this study available during the publication process of this work (Daly et al, 2023) confirm L and LL ordinary chondrites as the best meteorite analogues for Didymos. Considering that typical grain density of such meteorite complexes is in the 3500-3600 kg/m 3 range, the system bulk density is compatible with at least 30% bulk porosity of its components.…”

“…Right after the completion of this study, the DART spacecraft successfully impacted Dimorphos, and first results derived from the images of both the DRACO camera on board DART and the LEIA and LUKE cameras on board the CubeSat LICIACube (ASI: Agenzia Spaziale Italiana) have been published (Daly et al, 2023). Daly et al (2023) report a set of freshly estimated values for the critical parameters in this study: the mass of the system, (5.6 ± 0.5) × 10 11 kg; the equatorial extents, 850±5 m on average; the equivalent diameter of both Didymos, 761±26 m, and Dimorphos, 151 ± 5 m (uncertainties are given at 1 − 𝜎 level). Therefore, the mass of Didymos can also be easily estimated, assuming equal density for the two bodies.…”

“…At equal critical spin rate, the relationship between the density of the oblate shaped and the spherical body is 𝜌 ′ ∕𝜌 = 𝑎∕𝑐. E.g., for an oblate body with 𝑎∕𝑐 = 1.37 (the case of Didymos, as its extent along spin axis is estimated to be 620±15 m by Daly et al (2023)), the critical density is 𝜌 ′ = 2924 kg∕m 3 , while, for an equal mass spherical Didymos, it would be 𝜌 = 2134 kg∕m 3 .…”

Asteroid collision shows how much amateur astronomers have to offer

“…These skywatchers are among the authors of a study in Nature that describes how the asteroid, named Dimorphos, became temporarily brighter and redder as the spacecraft hit it 1 . One of five papers about the impact published in Nature [1][2][3][4][5] , it describes a real-time view of a cosmic collision -similar to that when Comet Shoemaker-Levy 9 slammed into Jupiter in July 1994.…”