Mercury’s moment of inertia from spin and gravity data
نویسندگان
چکیده
Earth-based radar observations of the spin state of Mercury at 35 epochs between 2002 and 2012 reveal that its spin axis is tilted by (2.04 ± 0.08) arcminutes with respect to the orbit normal. The direction of the tilt suggests that Mercury is in or near a Cassini state. Observed rotation rate variations clearly exhibit an 88-day libration pattern which is due to solar gravitational torques acting on the asymmetrically shaped planet. The amplitude of the forced libration, (37.8± 1.4) arcseconds, corresponds to a longitudinal displacement of ∼450 m at the equator. Combining these measurements of the spin properties with second-degree gravitational harmonics [Smith et al., 2012] provides an estimate of the polar moment of inertia of Mercury C/MR = 0.346±0.014, where M and R are Mercury’s mass and radius. The fraction of the moment that corresponds to the outer librating shell, which can be used to estimate the size of the core, is Cm/C = 0.438± 0.024.
منابع مشابه
Mercury’s Internal Structure
We describe the current state of knowledge about Mercury’s interior structure. We review the available observational constraints, including mass, size, density, gravity field, spin state, composition, and tidal response. These data enable the construction of models that represent the distribution of mass inside Mercury. In particular, we infer radial profiles of the pressure, density, and gravi...
متن کاملTitan ’ s spin , gravity , and moments of inertia
Introduction Analysis of Doppler tracking data and radar images from the Cassini spacecraft have recently provided estimates of the low degree gravity field [1], and spin pole direction [2] of Titan. We examine implications of these measurements for the internal structure and rotational dynamics of that body. We derive separate estimates of the polar moment of inertia of Titan from the degree t...
متن کاملReal-time Roll Angle Estimation for Two-wheeled Vehicles
An original method for the real-time estimation of the roll angle using low-cost sensors in two-wheeled vehicles is proposed. The roll angle greatly affects the dynamics of singletrack vehicles and its estimation is essential in control systems such as ABS, Traction Control, as well as Curve and Collision Warning, or even active suspensions. The proposed method uses a non-linear Kalman filter, ...
متن کاملGravity field and internal structure of Mercury from MESSENGER.
Radio tracking of the MESSENGER spacecraft has provided a model of Mercury's gravity field. In the northern hemisphere, several large gravity anomalies, including candidate mass concentrations (mascons), exceed 100 milli-Galileos (mgal). Mercury's northern hemisphere crust is thicker at low latitudes and thinner in the polar region and shows evidence for thinning beneath some impact basins. The...
متن کاملThe Vesta gravity field, spin pole and rotation period, landmark positions, and ephemeris from the Dawn tracking and optical data
The Vesta gravity field and related physical parameters have been precisely measured using 10-months of radiometric Doppler and range data and optical landmark tracking from the Dawn spacecraft. The gravity field, orientation parameters, landmark locations, and Vesta’s orbit are jointly estimated. The resulting spherical harmonic gravity field has a half-wavelength resolution of 42 km (degree 2...
متن کامل