AIDA DART asteroid deflection test: Planetary defense and science objectives

https://hal-insu.archives-ouvertes.fr/insu-01667223/document

European component of the AIDA mission to a binary asteroid: Characterization and interpretation of the impact of the DART mission

This chapter reviews the estimates of the dust-to-gas and refractory-to-ice mass ratios derived from Rosetta measurements in the lost materials and the nucleus of 67P/Churyumov-Gerasimenko, respectively. First, the measurements by Rosetta instruments are described, as well as relevant characteristics of 67P. The complex picture of the activity of 67P, with its extreme North-South seasonal asymmetry, is presented. Individual estimates of the dust-to-gas and refractory-to-ice mass ratios are then presented and compared, showing wide ranges of plausible values. Rosetta’s wealth of information suggests that estimates of the dust-to-gas mass ratio made in cometary comae at a single point in time may not be fully representative of the refractory-to-ice mass ratio within the cometary nuclei being observed.

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Dust-to-Gas and Refractory-to-Ice Mass Ratios of Comet 67P/Churyumov-Gerasimenko from Rosetta Observations

Some years ago, the consensus was that asteroid (16) Psyche was almost entirely metal. New data on density, radar properties, and spectral signatures indicate that the asteroid is something perhaps even more enigmatic: a mixed metal and silicate world. Here we combine observations of Psyche with data from meteorites and models for planetesimal formation to produce the best current hypotheses for Psyche's properties and provenance. Psyche's bulk density appears to be between 3,400 and 4,100 kg m-3. Psyche is thus predicted to have between ~30 and ~60 vol% metal, with the remainder likely low-iron silicate rock and not more than ~20% porosity. Though their density is similar, mesosiderites are an unlikely analog to bulk Psyche because mesosiderites have far more iron-rich silicates than Psyche appears to have. CB chondrites match both Psyche's density and spectral properties, as can some pallasites, although typical pallasitic olivine contains too much iron to be consistent with the reflectance spectra. Final answers, as well as resolution of contradictions in the data set of Psyche physical properties, for example, the thermal inertia measurements, may not be resolved until the NASA Psyche mission arrives in orbit at the asteroid. Despite the range of compositions and formation processes for Psyche allowed by the current data, the science payload of the Psyche mission (magnetometers, multispectral imagers, neutron spectrometer, and a gamma-ray spectrometer) will produce data sets that distinguish among the models.

/pdf/observations-meteorites-and-models-a-preflight-assessment-of-4zx35m6hhd.pdf

Observations, Meteorites, and Models: A Preflight Assessment of the Composition and Formation of (16) Psyche.

Many asteroids and trans-neptunian objects have satellites: the tally stands at over 150 on http://tinyurl.com/dweqf
 . The smallest of these binary systems are main-belt and near-Earth asteroids, but the environments of these two types of object are very different, making it difficult to work out a common mechanism to explain their formation. Now Walsh et al. present a model that fits the bill. Properties of the observed main-belt and near-Earth asteroids with satellites are matched by simulations involving the slow spinup of a 'rubble pile' asteroid via the thermal YORP effect (where radiation from an irregular body exerts a net force on that body). The mass shed from the equator of a spinning body accretes into a satellite if the material consists of particles undergoing energy-dissipating collisions. Binary asteroids are created by the slow spin up of a 'rubble pile' asteroid via the thermal YORP effect (where radiation from an irregularly shaped body exerts a net force on the body). The mass shed from the equator of a critically spinning body accretes into a satellite if the material is collisionally dissipative. Asteroids with satellites are observed throughout the Solar System, from subkilometre near-Earth asteroid pairs to systems of large and distant bodies in the Kuiper belt. The smallest and closest systems are found among the near-Earth and small inner main-belt asteroids, which typically have rapidly rotating primaries and close secondaries on circular orbits. About 15 per cent of near-Earth and main-belt asteroids with diameters under 10 km have satellites1,2. The mechanism that forms such similar binaries in these two dynamically different populations was hitherto unclear. Here we show that these binaries are created by the slow spinup of a ‘rubble pile’ asteroid by means of the thermal YORP (Yarkovsky–O’Keefe–Radzievskii–Paddack) effect. We find that mass shed from the equator of a critically spinning body accretes into a satellite if the material is collisionally dissipative and the primary maintains a low equatorial elongation. The satellite forms mostly from material originating near the primary’s surface and enters into a close, low-eccentricity orbit. The properties of binaries produced by our model match those currently observed in the small near-Earth and main-belt asteroid populations, including 1999 KW4 (refs 3, 4).

Rotational Breakup as the Origin of Small Binary Asteroids

https://hal-insu.archives-ouvertes.fr/insu-01624991/document

R. Granados-Alfaro

Papers

Direct Observations of Asteroid Interior and Regolith Structure: Science Measurement Requirements