Large Longitude Libration of Mercury Reveals a Molten Core

  title={Large Longitude Libration of Mercury Reveals a Molten Core},
  author={J. Margot and S. Peale and R. Jurgens and M. Slade and I. Holin},
  pages={710 - 714}
Observations of radar speckle patterns tied to the rotation of Mercury establish that the planet occupies a Cassini state with obliquity of 2.11 ± 0.1 arc minutes. The measurements show that the planet exhibits librations in longitude that are forced at the 88-day orbital period, as predicted by theory. The large amplitude of the oscillations, 35.8 ± 2 arc seconds, together with the Mariner 10 determination of the gravitational harmonic coefficient C22, indicates that the mantle of Mercury is… Expand

Topics from this paper

Resonant forcing of Mercury's libration in longitude
The period of free libration of Mercury's longitude about the position it would have had if it were rotating uniformly at 1.5 times its orbital mean motion is close to resonance with Jupiter'sExpand
First MESSENGER orbital observations of Mercury's librations
We have coregistered laser altimeter profiles from 3 years of MErcury Surface, Space ENvironment, GEochemistry, and Ranging (MESSENGER) orbital observations with stereo digital terrain models toExpand
Latitudinal librations of Mercury with a fluid core
Abstract In the framework of the space missions to Mercury, an accurate model of rotation is needed. Librations around the 3:2 spin-orbit resonance as well as latitudinal librations have to beExpand
Planetary perturbations on Mercury’s libration in longitude
Two space missions dedicated to Mercury (MESSENGER and BepiColombo) aim at understanding its rotation and confirming the existence of a liquid core. This double challenge requires much more accurateExpand
The influence of Mercury’s inner core on its physical libration
Abstract As Mercury orbits the Sun, gravitational torques on its equatorial elliptical shape give rise to a planetary libration. The amplitude of Mercury’s libration, as determined from Earth-basedExpand
Theory of longitude librations of mercury based on the ground radar observations
On the basis of the analytic theory of longitude libration of Mercury (in the elliptical orbit) and the data of determination of values of the angular velocity of Mercury rotation obtained usingExpand
Titan's Rotation Reveals an Internal Ocean and Changing Zonal Winds
Cassini radar observations of Saturn's moon Titan over several years show that its rotational period is changing and is different from its orbital period, which is consistent with seasonal exchange of angular momentum between the surface and Titan's dense superrotating atmosphere. Expand
Analytical model of the long-period forced longitude librations of Mercury
Abstract The shaking of Mercury’s orbit by the planets forces librations in longitude in addition to those at harmonics of the orbital period that have been used to detect Mercury’s molten core. WeExpand
The libration and interior structure of large icy satellites and Mercury
Longitudinal librations are periodic changes in the rotation angle of a planet or satellite. Their observation and subsequent interpretation have profoundly increased our understanding of theExpand
The Geophysics of Mercury: Current Status and Anticipated Insights from the MESSENGER Mission
Abstract Current geophysical knowledge of the planet Mercury is based upon observations from ground-based astronomy and flybys of the Mariner 10 spacecraft, along with theoretical and computationalExpand


Mercury's rotation axis and period
Abstract Recent measurements made from high-resolution Mariner 10 photography of the planet Mercury yield a rotation period of 58.6461 ± 0.005 days, in excellent agreement with the period requiredExpand
A Procedure for Determining the Nature of Mercury's Core
We review the assertion that the precise measurement of the second degree gravitational harmonic coefficients, the obliquity, and the amplitude of the physical libration in longitude, C20, C22, θ,Expand
Rotational Period of the Planet Mercury
IN a recent communication by S. J. Peale and T. Gold1 the rotational period of Mercury, determined from radar Doppler-spread measurements to be 59 ± 5 days2, has been explained in terms of a solarExpand
Rotation of the Planet Mercury
SOLAR tidal friction must be an intense effect for Mercury, and it must be expected that the planet's spin would have relaxed from any original value to one that is under the control of this effectExpand
Some aspects of core formation in Mercury
Evidence for a large metallic core in Mercury is all indirect; the internal magnetic field may imply a convective dynamo; the surface geology is suggestive of large-scale differentiation; and thermalExpand
The magnetic field of Mercury, 1
An updated analysis and interpretation are presented of the magnetic field observations obtained during the Mariner 10 encounter with the planet Mercury on March 29, 1974. The combination of dataExpand
Radar Mapping of Mercury: Full-Disk Images and Polar Anomalies
A random-code technique used at Arecibo to obtain delay-Doppler radar images of the full disk of Mercury revealed anomalously bright features at the north and south poles and a variety of more subdued reflectivity features ranging in size from hundreds to thousands of kilometers. Expand
Does Mercury have a molten core?
THE discovery of an intrinsic magnetic field for the planet Mercury by Mariner 10 (ref. 1) and its preferred source in an internal dynamo2 imply the existence of a conducting molten core. We proposeExpand
Radar mapping of Mercury's polar anomalies
GROUND-based radar observations of Mercury have revealed unusually strong, highly depolarized echoes from the north1,2 and south2 poles. These anomalous echoes have been cited as evidence of polarExpand
The mass, gravity field, and ephemeris of Mercury
This paper represents a final report on the gravity analysis of radio Doppler and range data generated by the Deep Space Network (DSN) with Mariner 10 during two of its encounters with Mercury inExpand