Porosity Evolution in Metallic Asteroids: Implications for the Origin and Thermal History of Asteroid 16 Psyche

Nichols-Fleming, Fiona; Evans, A. J.; Johnson, Brandon C.; Sori, Michael M.

doi:10.1029/2021je007063

Cited by 8 publications

(15 citation statements)

References 52 publications

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“…The IVA irons are inferred to sample materials from different depths of its parent body, from near‐surface to central regions, which is typically inferred as evidence for the catastrophic breakup of their parent body. The cloudy‐zone micro‐structures of the IVA irons suggest that they were still inside their parent body at temperatures of ∼500–600 K. This implies that the disruption likely occurred at temperatures below ∼500 K, which is probably low enough for the body to remain porous after the disruption event (Nichols‐Fleming et al., 2022). Although the IVA irons are not necessarily from Psyche, their thermal and collisional history implies that disruption may occur after the cooling of Psyche‐sized metallic bodies.…”

Section: Implications For Psychementioning

confidence: 99%

“…If Psyche is a metallic rubble pile, its formation history should include both a mantle‐stripping event and a porosity‐adding event. Mantle stripping is likely associated with one or repeated hit‐and‐run collisions (e.g., Asphaug & Reufer, 2014; Asphaug et al., 2006), which likely occurred in the first few million years following solar system formation, in which case the core cannot cool fast enough to preserve porosity against viscous compaction (Nichols‐Fleming et al., 2022). If a disruptive collision occurred after the exposed core had sufficiently cooled (e.g., tens of millions of years after solar system formation), the collision fragments could remain sufficiently cold, since heating from disruptive collisions is thought to be small (Keil et al., 1997; Love & Ahrens, 1996).…”

Section: Implications For Psychementioning

confidence: 99%

“…Viscous compaction through thermally activated creep is thought to occur at high temperatures in planetesimals that were formed early enough to be heated by the decay of the short‐lived radio‐nuclide 26 Al (e.g., Lichtenberg et al., 2016; Neumann et al., 2020; Nichols‐Fleming et al., 2022). In bodies of typical asteroid sizes (up to a few hundred kilometers in diameter), heating from disruptive impacts is almost negligible because most materials that are strongly heated by the impacts would escape instead of being captured by re‐accreted rubble piles (e.g., Keil et al., 1997; Love & Ahrens, 1996).…”

Section: Introductionmentioning

confidence: 99%

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Cold Compaction and Macro‐Porosity Removal in Rubble‐Pile Asteroids: 2. Applications

2022

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Models of asteroid collisional evolution suggest that many asteroids are gravitationally‐bound rubble piles. Although rubble piles may be expected to retain large void fractions, compaction may reduce the porosity. We apply models for cold compaction of rubble‐pile bodies developed in a companion paper toward observations of asteroid densities. The model for chondritic boulders is applied to S‐type (stony) and C‐type (carbonaceous) asteroids. The relation between density and size of S‐type asteroids is largely explained by cold compaction of rubble piles through fracturing of boulders, under the assumption that boulder size distributions are narrow before fracturing and fractal‐like afterward. The density variation of C‐type asteroids can only partly be explained by this mechanism, and the removal of micro‐voids inside the boulders would be required to match observations. The model for metal boulders is applied to M‐type asteroids, and the results suggest that, because of cold welding between metal boulders and the high yield strength of metal for either ductile or brittle‐like deformation, metallic rubble piles can preserve large (≳50%) porosities if the boulders are ∼1 m in size. This implies that M‐type asteroids such as Psyche and Kleopatra may be purely metallic, even though their densities are less than half that of iron. We also consider the hypothesis that Psyche is a primitive body of a CB chondrite‐like material. Assuming that the strength of CB chondrite is controlled by a silicate matrix, we predict that the density of a Psyche‐sized rubble pile of CB chondrite is higher than that of Psyche.

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Section: Implications For Psychementioning

confidence: 99%

Section: Implications For Psychementioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

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Cold Compaction and Macro‐Porosity Removal in Rubble‐Pile Asteroids: 2. Applications

2022

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“…This inconsistency may be understandable if Psyche is a rubble-pile asteroid having a very high porosity (>∼50%). Also, Nichols-Fleming et al (2022) recently indicated that Psyche might be difficult to reconcile with a fully metallic structure by showing that high porosity (∼40%) cannot be sustainable owing to the porosity removal by thermal evolution. They found that a Psyche-sized body must cool down below 800 K prior to porosity-adding events (i.e., disruptive impacts) to maintain sufficient porosity (∼40%) until the present.…”

Section: Introductionmentioning

confidence: 99%

A Numerical Approach Using a Finite Element Model to Constrain the Possible Interior Layout of (16) Psyche

Kim

Hirabayashi

2022

Planet. Sci. J.

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Asteroid (16) Psyche (278 × 238 × 171 km in size) is notable for the largest M-type asteroid and has the high radar albedo (0.34 ± 0.08) among the main-belt asteroids. The object is likely a mixture of metal and silicates because of its lower bulk density (∼4.0 g cm−3) than metallic materials (∼7.5 g cm−3) and observations inferring the existence of silicate materials on the surface. Here, we numerically investigate the interior layout when the structure of Psyche consists of a spherical iron core and two types of the silicate-rich layers (compressed and uncompressed ones) resulting from the compaction process (later known as a three-layer model). We develop an inverse problem algorithm to determine the layout distribution by combining a finite element model approach that accounts for density variations and constrains pressure-based crushing conditions. The results show that, given the crushing limit of 10 MPa, the smallest core size likely reaches 72 km in radius, and the silicate-rich layer, consisting of both compressed and uncompressed regions, has a thickness ranging up to 68 km. To support the localized metal concentration at the crater-like region detected in the recent radar observation, we give more constraints on the minimum core size, which takes up to 34%–40% of the entire size of Psyche. Our study also addresses that the ferrovolcanic surface eruptions could still be a source of metal-rich materials. Finally, while the differentiated structure having a spherical core condition is just part of potential scenarios, the present study infers that the core and compressed layer conditions likely control the surface condition. Further investigations will provide key information for observable properties on NASA’s Psyche mission to provide insight into its evolution history.

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“…This inconsistency may be understandable if Psyche is a rubble-pile asteroid having a very high porosity (> ∼50%). Also, Nichols-Fleming et al (2022) recently indicated that Psyche might be difficult to reconcile with a fully metallic structure by showing that high porosity (∼40%) cannot be sustainable due to the porosity removal by thermal evolution. They found that a Psyche-sized body must cool down below 800 K prior to porosity-adding events (i.e., disruptive impacts) to persist the sufficient porosity (∼40%) until the present.…”

mentioning

confidence: 99%

A numerical approach using a finite element model to constrain the possible interior layout of (16) Psyche

Kim¹,

Hirabayashi²

2022

Preprint

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Asteroid ( 16) Psyche (278×238×171 km in size) is notable for the largest M-type asteroid and has the high radar albedo (0.34±0.08) among the main-belt asteroids. The object is likely a mixture of metal and silicates because of its lower bulk density (∼4.0 g cm −3 ) than metallic materials (∼7.5 g cm −3 ) and observations inferring the existence of silicate materials on the surface. Here, we numerically investigate the interior layout when the structure of Psyche consists of a spherical iron core and two types of the silicate-rich layers (compressed and uncompressed ones) resulting from the compaction process (later known as a Three-layer model). We develop an inverse problem algorithm to determine the layout distribution by combining a Finite Element Model (FEM) approach that accounts for density variations and constrains pressure-based crushing conditions. The results show that given the crushing limit of 10 MPa the smallest core size likely reaches 72 km in radius, and the silicate-rich layer, consisting of both compressed and uncompressed regions, has a thickness ranging up to 68 km. To support the localized metal concentration at the crater-like region detected in the recent radar observation, we give more constraints on the minimum core size which takes up to 34 -40 % of the entire size of Psyche. Our study also addresses that the ferrovolcanic surface eruptions could still be a source of metal-rich materials. Finally, while the differentiated structure having a spherical core condition is just part of potential scenarios, the present study infers that the core and compressed layer conditions likely control the surface condition. Further investigations will provide key information for observable properties on NASA's Psyche mission to provide insight into its evolution history.

show abstract

Porosity Evolution in Metallic Asteroids: Implications for the Origin and Thermal History of Asteroid 16 Psyche

Cited by 8 publications

References 52 publications

Cold Compaction and Macro‐Porosity Removal in Rubble‐Pile Asteroids: 2. Applications

Cold Compaction and Macro‐Porosity Removal in Rubble‐Pile Asteroids: 2. Applications

A Numerical Approach Using a Finite Element Model to Constrain the Possible Interior Layout of (16) Psyche

A numerical approach using a finite element model to constrain the possible interior layout of (16) Psyche

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