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Fundamental properties of the planet Venus, such as its internal mass distribution and variations in length of day, have remained unknown. We used Earth-based observations of radar speckles tied to the rotation of Venus obtained in 2006-2020 to measure its spin axis orientation, spin precession rate, moment of inertia, and length-of-day variations. Venus is tilted by 2.6392 $pm$ 0.0008 degrees ($1sigma$) with respect to its orbital plane. The spin axis precesses at a rate of 44.58 $pm$ 3.3 arcseconds per year ($1sigma$), which gives a normalized moment of inertia of 0.337 $pm$ 0.024 and yields a rough estimate of the size of the core. The average sidereal day on Venus in the 2006-2020 interval is 243.0226 $pm$ 0.0013 Earth days ($1sigma$). The spin period of the solid planet exhibits variations of 61 ppm ($sim$20 minutes) with a possible diurnal or semidiurnal forcing. The length-of-day variations imply that changes in atmospheric angular momentum of at least $sim$4% are transferred to the solid planet.
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Constraining Jupiters internal structure is crucial for understanding its formation and evolution history. Recent interior models of Jupiter that fit Junos measured gravitational field suggest an inhomogeneous interior and potentially the existence of a diluted core. These models, however, strongly depend on the model assumptions and the equations of state used. A complementary modelling approach is to use empirical structure models. These can later be used to reveal new insights on the planetary interior and be compared to standard models. Here we present empirical structure models of Jupiter where the density profile is constructed by piecewise-polytropic equations. With these models we investigate the relation between the normalized moment of inertia (MoI) and the gravitational moments $J_2$ and $J_4$. Given that only the first few gravitational moments of Jupiter are measured with high precision, we show that an accurate and independent measurement of the MoI value could be used to further constrain Jupiters interior. An independent measurement of the MoI with an accuracy better than $sim 0.1%$ could constrain Jupiters core region and density discontinuities in its envelope. We find that models with a density discontinuity at $sim$ 1 Mbar, as would produce a presumed hydrogen-helium separation, correspond to a fuzzy core in Jupiter. We next test the appropriateness of using polytropes, by comparing them with empirical models based on polynomials. We conclude that both representations result in similar density profiles and ranges of values for quantities like core mass and MoI.
Japanese Venus Climate Orbiter/AKATSUKI was proposed in 2001 with strong support by international Venus science community and approved as an ISAS (The Institute of Space and Astronautical Science) mission soon after the proposal. The mission life we expected was more than two Earth years in Venus orbit. AKATSUKI was successfully launched at 06:58:22JST on May 21, 2010, by H-IIA F17. After the separation from H-IIA, the telemetry from AKATSUKI was normally detected by DSN Goldstone station (10:00JST) and the solar cell paddles deployment was confirmed. After a successful cruise, the malfunction happened on the propulsion system during the Venus orbit insertion (VOI) on Dec 7, 2010. The engine shut down before the planned reduction in speed to achieve. The spacecraft did not enter the Venus orbit, but entered an orbit around the Sun with a period of 203 days. Most of the fuel still had remained, but the orbital maneuvering engine was found to be broken and unusable. However, we have found an alternate way of achieving orbit by using only the reaction control system (RSC). We had adopted the alternate way for orbital maneuver and three minor maneuvers in Nov 2011 were successfully done so that AKATSUKI would meet Venus in 2015. We are considering several scenarios for VOI using only RCS.
In this work, the normal density $rho_n$ and moment of inertia of a moving superfluid are investigated. We find that, even at zero temperature, there exists a finite normal density for the moving superfluid. When the velocity of superfluid reaches sound velocity, the normal density becomes total mass density $rho$, which indicates that the system losses superfluidity. At the same time, the Landaus critical velocity also becomes zero. The existence of the non-zero normal density is attributed to the coupling between the motion of superflow and density fluctuation in transverse directions. With Josephson relation, the superfluid density $rho_s$ is also calculated and the identity $rho_s+rho_n=rho$ holds. Further more, we find that the finite normal density also results in a quantized moment of inertia in a moving superfluid trapped by a ring. The normal density and moment of inertia at zero temperature could be verified experimentally by measuring the angular momentum of a moving superfluid in a ring trap.
This work analyzes the X-ray, EUV and UV emission apparently coming from the Earth-facing (dark) side of Venus as observed with Hinode/XRT and SDO/AIA during a transit across the solar disk occurred in 2012. We have measured significant X-Ray, EUV and UV flux from Venus dark side. As a check we have also analyzed a Mercury transit across the solar disk, observed with Hinode/XRT in 2006. We have used the latest version of the Hinode/XRT Point Spread Function (PSF) to deconvolve Venus and Mercury X-ray images, in order to remove possible instrumental scattering. Even after deconvolution, the flux from Venus shadow remains significant while in the case of Mercury it becomes negligible. Since stray-light contamination affects the XRT Ti-poly filter data from the Venus transit in 2012, we performed the same analysis with XRT Al-mesh filter data, which is not affected by the light leak. Even the Al-mesh filter data show residual flux. We have also found significant EUV (304 A, 193 A, 335 A) and UV (1700 A) flux in Venus shadow, as measured with SDO/AIA. The EUV emission from Venus dark side is reduced when appropriate deconvolution methods are applied; the emission remains significant, however. The light curves of the average flux of the shadow in the X-ray, EUV, and UV bands appear different as Venus crosses the solar disk, but in any of them the flux is, at any time, approximately proportional to the average flux in a ring surrounding Venus, and therefore proportional to the average flux of the solar regions around Venus obscuring disk line of sight. The proportionality factor depends on the band. This phenomenon has no clear origin; we suggest it may be due to scatter occurring in the very long magnetotail of Venus.
An essential property of magnetic devices is the relaxation rate in magnetic switching which strongly depends on the energy dissipation and magnetic inertia of the magnetization dynamics. Both parameters are commonly taken as a phenomenological entities. However very recently, a large effort has been dedicated to obtain Gilbert damping from first principles. In contrast, there is no ab initio study that so far has reproduced measured data of magnetic inertia in magnetic materials. In this letter, we present and elaborate on a theoretical model for calculating the magnetic moment of inertia based on the torque-torque correlation model. Particularly, the method has been applied to bulk bcc Fe, fcc Co and fcc Ni in the framework of the tight-binding approximation and the numerical values are comparable with recent experimental measurements. The theoretical results elucidate the physical origin of the moment of inertia based on the electronic structure. Even though the moment of inertia and damping are produced by the spin-orbit coupling, our analysis shows that they are caused by undergo different electronic structure mechanisms.
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