Where can the water go? Giant impacts and the deep mantle

ABSTRACT The NASA’s Kepler mission discovered ∼700 planets in multiplanet systems containing three or more transiting bodies, many of which are super-Earths and mini-Neptunes in compact configurations. Using N-body simulations, we examine the in situ, final stage assembly of multiplanet systems via the collisional accretion of protoplanets. Our initial conditions are constructed using a subset of the Kepler five-planet systems as templates. Two different prescriptions for treating planetary collisions are adopted. The simulations address numerous questions: Do the results depend on the accretion prescription?; do the resulting systems resemble the Kepler systems, and do they reproduce the observed distribution of planetary multiplicities when synthetically observed?; do collisions lead to significant modification of protoplanet compositions, or to stripping of gaseous envelopes?; do the eccentricity distributions agree with those inferred for the Kepler planets? We find that the accretion prescription is unimportant in determining the outcomes. The final planetary systems look broadly similar to the Kepler templates adopted, but the observed distributions of planetary multiplicities or eccentricities are not reproduced, because scattering does not excite the systems sufficiently. In addition, we find that ∼1 per cent of our final systems contain a co-orbital planet pair in horseshoe or tadpole orbits. Post-processing the collision outcomes suggests that they would not significantly change the ice fractions of initially ice-rich protoplanets, but significant stripping of gaseous envelopes appears likely. Hence, it may be difficult to reconcile the observation that many low-mass Kepler planets have H/He envelopes with an in situ formation scenario that involves giant impacts after dispersal of the gas disc.

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Superionic iron oxide–hydroxide in Earth’s deep mantle

Nature Geoscience ◽

10.1038/s41561-021-00696-2 ◽

2021 ◽

Vol 14 (3) ◽

pp. 174-178 ◽

Cited By ~ 1

Author(s):

Mingqiang Hou ◽

Yu He ◽

Bo Gyu Jang ◽

Shichuan Sun ◽

Yukai Zhuang ◽

...

Keyword(s):

Iron Oxide ◽

Oxide Hydroxide ◽

Deep Mantle

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Planetary embryo collisions and the wiggly nature of extreme debris discs

Monthly Notices of the Royal Astronomical Society ◽

10.1093/mnras/stab106 ◽

2021 ◽

Vol 502 (2) ◽

pp. 2984-3002

Author(s):

Lewis Watt ◽

Zoe Leinhardt ◽

Kate Y L Su

Keyword(s):

Equations Of State ◽

Semimajor Axis ◽

Central Star ◽

Impact Angle ◽

Narrow Region ◽

Term Variation ◽

Planetary Embryo ◽

Smoothed Particle ◽

Giant Impacts ◽

Post Impact

ABSTRACT In this paper, we present results from a multistage numerical campaign to begin to explain and determine why extreme debris disc detections are rare, what types of impacts will result in extreme debris discs and what we can learn about the parameters of the collision from the extreme debris discs. We begin by simulating many giant impacts using a smoothed particle hydrodynamical code with tabulated equations of state and track the escaping vapour from the collision. Using an N-body code, we simulate the spatial evolution of the vapour generated dust post-impact. We show that impacts release vapour anisotropically not isotropically as has been assumed previously and that the distribution of the resulting generated dust is dependent on the mass ratio and impact angle of the collision. In addition, we show that the anisotropic distribution of post-collision dust can cause the formation or lack of formation of the short-term variation in flux depending on the orientation of the collision with respect to the orbit around the central star. Finally, our results suggest that there is a narrow region of semimajor axis where a vapour generated disc would be observable for any significant amount of time implying that giant impacts where most of the escaping mass is in vapour would not be observed often but this does not mean that the collisions are not occurring.

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Deep mantle melting, global water circulation and its implications for the stability of the ocean mass

Progress in Earth and Planetary Science ◽

10.1186/s40645-020-00379-3 ◽

2020 ◽

Vol 7 (1) ◽

Author(s):

Shun-ichiro Karato ◽

Bijaya Karki ◽

Jeffrey Park

Keyword(s):

Phase Transformation ◽

Water Content ◽

Sea Level ◽

High Water ◽

Water Circulation ◽

Mantle Melting ◽

High Water Content ◽

Mineral Physics ◽

Deep Mantle ◽

Global Water

AbstractOceans on Earth are present as a result of dynamic equilibrium between degassing and regassing through the interaction with Earth’s interior. We review mineral physics, geophysical, and geochemical studies related to the global water circulation and conclude that the water content has a peak in the mantle transition zone (MTZ) with a value of 0.1–1 wt% (with large regional variations). When water-rich MTZ materials are transported out of the MTZ, partial melting occurs. Vertical direction of melt migration is determined by the density contrast between the melts and coexisting minerals. Because a density change associated with a phase transformation occurs sharply for a solid but more gradually for a melt, melts formed above the phase transformation depth are generally heavier than solids, whereas melts formed below the transformation depth are lighter than solids. Consequently, hydrous melts formed either above or below the MTZ return to the MTZ, maintaining its high water content. However, the MTZ water content cannot increase without limit. The melt-solid density contrast above the 410 km depends on the temperature. In cooler regions, melting will occur only in the presence of very water-rich materials. Melts produced in these regions have high water content and hence can be buoyant above the 410 km, removing water from the MTZ. Consequently, cooler regions of melting act as a water valve to maintain the water content of the MTZ near its threshold level (~ 0.1–1.0 wt%). Mass-balance considerations explain the observed near-constant sea-level despite large fluctuations over Earth history. Observations suggesting deep-mantle melting are reviewed including the presence of low-velocity anomalies just above and below the MTZ and geochemical evidence for hydrous melts formed in the MTZ. However, the interpretation of long-term sea-level change and the role of deep mantle melting in the global water circulation are non-unique and alternative models are reviewed. Possible future directions of studies on the global water circulation are proposed including geodynamic modeling, mineral physics and observational studies, and studies integrating results from different disciplines.

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