Radar observations and a physical model of binary near-Earth asteroid 65803 Didymos, target of the DART mission

Naidu, Shantanu P.; Benner, L. A. M.; Brozović, M.; Nolan, M. C.; Ostro, S. J.; Margot, Jean-Luc; Giorgini, Jon D.; Hirabayashi, Toshi; Scheeres, Daniel J.; Pravec, Petr; Scheirich, P.; Magri, C.; Jao, Joseph S.

doi:10.1016/j.icarus.2020.113777

Cited by 131 publications

(201 citation statements)

References 47 publications

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“…Ground-based radar observations show that spheroidal shapes are dominant in observed objects [e.g., Taylor et al, 2012;Benner et al, 2015]. Among them are reported to be top shapes, some of which also have smaller satellites [e.g., Ostro et al, 2006;Brozović et al, 2011;Becker et al, 2015;Busch et al, 2011;Naidu et al, 2015Naidu et al, , 2020Walsh and Jacobson, 2015]. Some top shapes are rotating close to their spin limits at which surface materials may be about to be shed [Scheeres et al, 2006;Harris et al, 2009], while others like Ryugu are not [Watanabe et al, 2019].…”

Section: Rotational Evolution Of Top-shaped Asteroidsmentioning

confidence: 99%

Spin-driven evolution of asteroids' top-shapes at fast and slow spins seen from (101955) Bennu and (162173) Ryugu

Hirabayashi

Nakano

Tatsumi

et al. 2020

Icarus

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Proximity observations by OSIRIS-REx and Hayabusa2 provided clues on the shape evolution processes of the target asteroids, (101955) Bennu and (162173) Ryugu. Their oblate shapes with equatorial ridges, or the so-called top shapes, may have evolved due to their rotational conditions at present and in the past. Different shape evolution scenarios were previously proposed; Bennu's top shape may have been driven by surface processing, while Ryugu's may have been developed due to large deformation. These two scenarios seem to be inconsistent. Here, we revisit the structural analyses in earlier works and fill a gap to connect these explanations. We also apply a semi-analytical technique for computing the cohesive strength distribution in a uniformly rotating triaxial ellipsoid to characterize the global failure of top-shaped bodies. Assuming that the structure is uniform, our semi-analytical approach describes the spatial variations in failed regions at different spin periods; surface regions are the most sensitive at longer spin periods, while interiors fail structurally at shorter spin periods. This finding suggests that the shape evolution of a top shape may vary due to rotation and internal structure, which can explain the different evolution scenarios of Bennu's and Ryugu's top shapes. We interpret our results as the indications of top shapes' various evolution processes. Highlights • We reanalyzed results from FEM analyses for asteroids Bennu and Ryugu, the targets of OSIRIS-REx and Hayabusa2, respectively. • We also applied a semi-analytical approach to quantify how the failure modes of top shapes vary with spin. • Top shapes may evolve by two deformation modes: surface processing at low spin and internal failure at high spin.

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Section: Rotational Evolution Of Top-shaped Asteroidsmentioning

confidence: 99%

Spin-driven evolution of asteroids' top-shapes at fast and slow spins seen from (101955) Bennu and (162173) Ryugu

Hirabayashi

Nakano

Tatsumi

et al. 2020

Icarus

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“…In 2003, it was discovered that Didymos is a binary system (Pravec et al, 2003). The binary has a mutual orbit period of P orb ∼ 11.9217 h and a semi-major axis of a orb ∼ 1.19 km (Pravec et al, 2006;Naidu et al, 2020a). According to the binary mean separation and orbital period, Kepler's third law for assumed point masses implies a system mass of M sys ∼ 5.37 × 10 11 kg.…”

Section: The Didymos Systemmentioning

confidence: 99%

A benchmarking and sensitivity study of the full two-body gravitational dynamics of the DART mission target, binary asteroid 65803 Didymos

Agrusa

Richardson

Davis

et al. 2020

Icarus

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NASA's Double Asteroid Redirection Test (DART) is designed to be the first demonstration of a kinetic impactor for planetary defense against a small-body impact hazard. The target is the smaller component of the binary asteroid 65803 Didymos. We have conducted high-fidelity rigid full two-body simulations of the mutual dynamics of this system in a broad benchmarking exercise to find the best simulation methodologies, and to understand the sensitivity of the system to initial conditions. Due to the non-spherical shapes of the components and their close proximity, the components cannot be treated as point masses and so the dynamics differ significantly from a simple Keplerian orbit, necessitating the use of numerical simulations to fully capture the system's dynamics. We find that the orbit phase (angular position or true anomaly) of the secondary is highly sensitive to the initial rotation phase of the primary, making prediction of the secondary's location from numerical simulation challenging. Finally, we show that the DART impact should induce significant free and forced librations on the secondary. If this libration can be measured by ESA's recently approved follow-up spacecraft, Hera, it may be possible to constrain properties of the secondary's interior structure.

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“…Even the comet 67P/Churyumov-Gerasimenko -which is ten times larger than Ryugu -has sides with no obvious craters. Moreover, the diameters of the Didymos primary and secondary target bodies are only around 780 and 135m, respectively (4) . The two other options for absolute navigation -BSM and ICP -have their challenges.…”

Section: Preliminary Choices and Contributionmentioning

confidence: 99%

“…Analyse the algorithm performance under varying environmental conditions. 4. Select a reasonable algorithm configuration.…”

Section: Preliminary Choices and Contributionmentioning

confidence: 99%

“…APEX will be deployed at a distance of 10km from Didymos and then navigate to a 4-km circular orbit, where it will stay for several weeks. Next, APEX will navigate to the L 4 and L 5 points in the Didymos system, roughly 1200m from the centres of the primary and secondary body, whose mean diameters are around 780 and 135m, respectively (4) . The extended mission plan also includes periods where APEX will stay near the L 1 and L 2 points at a distance of around 180m from the centre of mass of the slightly elongated secondary body.…”

Section: Introductionmentioning

confidence: 99%

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Synthetic photometric landmarks used for absolute navigation near an asteroid

2020

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The need for autonomous location estimation in the form of optical navigation is an essential requirement for forthcoming deep space missions. While crater-based navigation might work well with larger bodies littered with craters, small sub-kilometer bodies do not necessarily have them. We have developed a new pose estimation method for absolute navigation based on photometric local feature extraction techniques thus making it suitable for missions that cannot rely on craters. The algorithm can be used by a navigation filter in conjunction with relative pose estimation such as visual odometry for additional robustness and accuracy. To estimate the position and orientation of the spacecraft in the asteroid-fixed coordinate frame, it uses navigation camera images in combination with other readily available information, such as orientation relative to the stars and the current time for an initial estimate of the asteroid rotation state. Evaluation of the algorithm when using different feature extractors is performed, on one hand, using Monte Carlo simulations and, on the other hand, using actual images taken by the Rosetta spacecraft orbiting the comet 67P/Churyumov–Gerasimenko. Our analysis, where four different feature extraction methods (AKAZE, ORB, SIFT, SURF) were compared, showed that AKAZE is most promising in terms of stability and accuracy.

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Radar observations and a physical model of binary near-Earth asteroid 65803 Didymos, target of the DART mission

Cited by 131 publications

References 47 publications

Spin-driven evolution of asteroids' top-shapes at fast and slow spins seen from (101955) Bennu and (162173) Ryugu

Spin-driven evolution of asteroids' top-shapes at fast and slow spins seen from (101955) Bennu and (162173) Ryugu

A benchmarking and sensitivity study of the full two-body gravitational dynamics of the DART mission target, binary asteroid 65803 Didymos

Synthetic photometric landmarks used for absolute navigation near an asteroid

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