Planet rotation
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Planet Rotation: Insights from Recent Research
Overview of Planetary Rotation Rates
The rotation rates of planets in our solar system vary significantly, with no clear correlation between a planet's size, distance from the sun, and its rotation period. For instance, Jupiter, the largest planet, completes a rotation in less than ten hours, while Mars, a much smaller planet, takes over twenty-four hours to rotate once1. This diversity in rotation periods highlights the complexity of planetary dynamics and the factors influencing them.
Rotation of Planet-Hosting Stars
Recent studies have explored the relationship between stellar rotation and the presence of planets. Data from the Kepler and Gaia missions indicate that stars hosting planets tend to rotate more slowly than those without planets. Specifically, planet-hosting stars rotate on average 1.63 days slower than their non-planet-hosting counterparts2. This finding suggests a potential link between the presence of planets and the angular momentum distribution in stellar systems, although detection biases may also play a role.
Origin of Planetary Rotation
The rotation of planets is influenced by the accretion of planetesimals during their formation. Planets acquire spin angular momentum from the relative motion of these planetesimals at impact. The rotation rate depends on the eccentricities of the planetesimals' orbits and the gravitational interactions within the planet's Hill Sphere. For planets with nearly circular orbits, rotation tends to be retrograde, while higher eccentricities can lead to prograde rotation3. This complex interplay of factors results in the diverse rotation rates observed in our solar system.
Equilibrium Rotation of Earth-like Exoplanets
The equilibrium rotation states of tidally evolved Earth-like exoplanets are often assumed to be synchronous with their orbital periods. However, many of these planets have eccentric orbits and dense atmospheres, leading to different equilibrium rotation states. Research shows that there are up to four distinct equilibrium rotation possibilities for such planets, including retrograde rotation. This indicates that synchronous rotation is unlikely for most known Earth-like exoplanets4.
Mercury's Unique Rotation
Mercury's rotation is particularly interesting due to its 3:2 spin-orbit resonance, where it rotates three times for every two orbits around the sun. This unique rotation period is influenced by the planet's rigid body dynamics and the gravitational forces exerted by the sun. Mercury's rotation also exhibits a libration with a period of 25 years, adding another layer of complexity to its rotational behavior5.
Differential Rotation in Stars and Planets
Differential rotation, where different parts of a star or planet rotate at different rates, is a key factor in understanding stellar and planetary dynamics. Observations and numerical simulations have shown that differential rotation is influenced by both hydrodynamic and magnetohydrodynamic processes. These findings help explain phenomena such as core-envelope shear in red giant stars and deviations from expected rotational behaviors in late-type stars10.
Conclusion
The study of planetary rotation reveals a complex interplay of factors, including accretion processes, gravitational interactions, and angular momentum distribution. While significant progress has been made in understanding these dynamics, ongoing research continues to uncover new insights into the rotational behaviors of planets and their host stars. This knowledge not only enhances our understanding of our own solar system but also informs the study of exoplanetary systems.
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Rotation of the Planets
The rotation of the planets is like an eclipse to a savage, an event which he knows occurs but of the cause of which he is ignorant.
The rotation of planet-hosting stars
Planet-hosting stars rotate on average 1.63 0.40 days slower than control samples, potentially indicating a physical link between planets and stellar rotation.
The origin of the systematic component of planetary rotation. I - Planet on a circular orbit
Planets accreted from small planetesimals rotate slowly in the prograde direction, with maximum prograde rotation rates comparable to those observed in our Solar System.
On the equilibrium rotation of Earth-like extra-solar planets
Earth-like extra-solar planets with eccentric orbits are unlikely to have synchronous equilibrium rotation, as there are at least four distinct possibilities, including one retrograde.
Theory of Rotation for the Planet Mercury
Mercury can rotate with a period of two-thirds of its revolution, and there is a libration with a period of 25 years.
On the Rotation of the Earth
The theory of the rotation of the Earth, based on absolute rigidity, admits of variations in terrestrial latitudes, but the observations show a period of revolution of nearly fourteen months.
Highly CitedThe four final rotation states of Venus
Venus can evolve into four possible rotation states, with most initial conditions driving it towards the configuration seen at present, but it can also begin with prograde rotation and then develop retrograde rotation while the obliquity goes towards zero.
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