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  1. Book ; Online: Is there a semi-molten layer at the base of the lunar mantle?

    Walterová, Michaela / Běhounková, Marie / Efroimsky, Michael

    2023  

    Abstract: Parameterised by the Love number $k_2$ and the tidal quality factor $Q$, and inferred from lunar laser ranging (LLR), tidal dissipation in the Moon follows an unexpected frequency dependence often interpreted as evidence for a highly dissipative, melt- ... ...

    Abstract Parameterised by the Love number $k_2$ and the tidal quality factor $Q$, and inferred from lunar laser ranging (LLR), tidal dissipation in the Moon follows an unexpected frequency dependence often interpreted as evidence for a highly dissipative, melt-bearing layer encompassing the core-mantle boundary. Within this, more or less standard interpretation, the basal layer's viscosity is required to be of order $10^{15}$ to $10^{16}$ Pa s, and its outer radius is predicted to extend to the zone of deep moonquakes. While the reconciliation of those predictions with the mechanical properties of rocks might be challenging, alternative lunar interior models without the basal layer are said to be unable to fit the frequency dependence of tidal $Q$. The purpose of our paper is to illustrate under what conditions the frequency-dependence of lunar tidal $Q$ can be interpreted without the need for deep-seated partial melt. Devising a simplified lunar model, in which the mantle is described by the Sundberg-Cooper rheology, we predict the relaxation strength and characteristic timescale of elastically-accommodated grain boundary sliding in the mantle that would give rise to the desired frequency dependence. Along with developing this alternative model, we test the traditional model with a basal partial melt; and we show that the two models cannot be distinguished from each other by the available selenodetic measurements. Additional insight into the nature of lunar tidal dissipation can be gained either by measurements of higher-degree Love numbers and quality factors or by farside lunar seismology.

    Comment: 44 pages, 15 figures, submitted to JGR: Planets
    Keywords Astrophysics - Earth and Planetary Astrophysics
    Subject code 551
    Publishing date 2023-01-06
    Publishing country us
    Document type Book ; Online
    Database BASE - Bielefeld Academic Search Engine (life sciences selection)

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  2. Book ; Online: Observed tidal evolution of Kleopatra's outer satellite

    Brož, M. / Ďurech, J. / Carry, B. / Vachier, F. / Marchis, F. / Hanuš, J. / Jorda, L. / Vernazza, P. / Vokrouhlický, D. / Walterová, M. / Behrend, R.

    2021  

    Abstract: The orbit of the outer satellite Alexhelios of (216) Kleopatra is already constrained by adaptive-optics astrometry, obtained with the VLT/SPHERE instrument. However, there is also a preceding occultation event in 1980 attributed to this satellite. ... ...

    Abstract The orbit of the outer satellite Alexhelios of (216) Kleopatra is already constrained by adaptive-optics astrometry, obtained with the VLT/SPHERE instrument. However, there is also a preceding occultation event in 1980 attributed to this satellite. Hereinafter, we try to link all observations, spanning 1980--2018. We find the nominal orbit exhibits an unexplained shift by $+60^\circ$ in the true longitude. Using both periodogram analysis and an $\ell = 10$ multipole model suitable for the motion of mutually interacting moons about the irregular body, we confirmed that it is not possible to adjust the respective osculating period $P_2$. Instead, we were forced to use a model with tidal dissipation (and increasing orbital periods) to explain the shift. We also analyzed light curves, spanning 1977--2021, and searched for the expected spin deceleration of Kleopatra. According to our best-fit model, the observed period rate is $\dot P_2 = (1.8\pm 0.1)\cdot 10^{-8}\,{\rm d}\,{\rm d}^{-1}$ and the corresponding time lag $\Delta t_2 = 42\,{\rm s}$ of tides, for the assumed value of the Love number $k_2 = 0.3$. It is the first detection of tidal evolution for moons orbiting 100-km asteroids. The corresponding dissipation factor $Q$ is comparable with other terrestrial bodies, albeit at a higher loading frequency $2|\omega-n|$. We also predict a secular evolution of the inner moon, $\dot P_1 = 5.0\cdot 10^{-8}$, as well as a spin deceleration of Kleopatra, $\dot P_0 = 1.9\cdot 10^{-12}$. In alternative models, with moons captured in the 3:2 mean-motion resonance or more massive moons, the respective values of $\Delta t_2$ are a factor of 2--3 lower. Future astrometric observations by direct imaging or occultations should allow to distinguish between these models, which is important for the internal structure and mechanical properties of (216) Kleopatra.

    Comment: accepted in A&A
    Keywords Astrophysics - Earth and Planetary Astrophysics
    Subject code 551
    Publishing date 2021-10-25
    Publishing country us
    Document type Book ; Online
    Database BASE - Bielefeld Academic Search Engine (life sciences selection)

    Full text online

    More links

    Kategorien

    Inter-library loan at ZB MED

    Your chosen title can be delivered directly to ZB MED Cologne location if you are registered as a user at ZB MED Cologne.

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