小惑星の軌道、形状はDART衝突後に変化した(NASA Study: Asteroid’s Orbit, Shape Changed After DART Impact)

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2024-03-19 NASA

NASAの歴史的なダブル小惑星リダイレクションテスト(DART)の後、JPLが主導する研究で、小惑星ディモルフォスの形状が変化し、その軌道が縮小したことが示されました。DARTが2022年9月26日に直径約170メートルの小惑星に衝突した後、その影響は軌道だけでなく、小惑星の形状も変化したことがPlanetary Science Journalに掲載された新しい研究で明らかになりました。

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DART衝突後の小惑星ディモルフォスの軌道と物理的特性評価 Orbital and Physical Characterization of Asteroid Dimorphos Following the DART Impact

Shantanu P. Naidu, Steven R. Chesley, Nicholas Moskovitz, Cristina Thomas, Alex J. Meyer, Petr Pravec, Peter Scheirich, Davide Farnocchia, Daniel J. Scheeres, Marina Brozovic,+
The Planetary Science Journal  Published:2024 March 19
DOI:10.3847/PSJ/ad26e7

小惑星の軌道、形状はDART衝突後に変化した(NASA Study: Asteroid’s Orbit, Shape Changed After DART Impact)

Abstract

The Double Asteroid Redirection Test (DART) mission impacted Dimorphos, the satellite of binary near-Earth asteroid (65803) Didymos, on 2022 September 26 UTC. We estimate the changes in the orbital and physical properties of the system due to the impact using ground-based photometric and radar observations, as well as DART camera observations. Under the assumption that Didymos is an oblate spheroid, we estimate that its equatorial and polar radii are 394 ± 11 m and 290 ± 16 m, respectively. We estimate that the DART impact instantaneously changed the along-track velocity of Dimorphos by −2.63 ± 0.06 mm s−1. Initially, after the impact, Dimorphos’s orbital period had changed by −32.7 minutes ± 16 s to 11.377 ± 0.004 hr. We find that over the subsequent several weeks the orbital period changed by an additional 34 ± 15 s, eventually stabilizing at 11.3674 ± 0.0004 hr. The total change in the orbital period was −33.25 minutes ±1.5 s. The postimpact orbit exhibits an apsidal precession rate of 6.7 ± 0fdg2 day−1. Under our model, this rate is driven by the oblateness parameter of Didymos, J2, as well as the spherical harmonics coefficients, C20 and C22, of Dimorphos’s gravity. Under the assumption that Dimorphos is a triaxial ellipsoid with a uniform density, its C20 and C22 estimates imply axial ratios, a/b and a/c, of about 1.3 and 1.6, respectively. Preimpact images from DART indicate Dimorphos’s shape was close to that of an oblate spheroid, and thus our results indicate that the DART impact significantly altered the shape of Dimorphos.

1701物理及び化学
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