Could Planet Nine be Causing Solar Obliquity Changes?

Solar Obliquity Induced by Planet Nine: Simple Calculation

Authors:

Lai et al

Abstract:

Bailey et al.~(2016) and Gomes et al.~(2016) recently suggested that the 6 degree misalignment between the Sun's rotational equator and the orbital plane of the major planets may be produced by the forcing from the hypothetical Planet Nine on an inclined orbit. Here we present a simple but accurate calculation of the effect, which provides a clear description of how the Sun's spin orientation depends on the property of Planet Nine in this scenario.

Obliquity-forced climate during the Early Triassic hothouse in China

Obliquity-forced climate during the Early Triassic hothouse in China

Authors:

Li et al

Abstract:

The start of the Mesozoic Era is marked by roughly 5 m.y. of Earth system upheavals, including unstable biotic recovery, repeated global warming, ocean anoxia, and perturbations in the global carbon cycle. Intervals between crises were comparably hospitable to life. The causes of these upheavals are unknown, but are thought to be linked to recurrent Siberian volcanism. Here, two marine sedimentary successions at Chaohu and Daxiakou (South China) are evaluated for paleoclimate change from astronomical forcing. In these sections, gamma-ray variations indicative of terrestrial weathering reveal enhanced obliquity cycling over prolonged intervals, characterized by a 32.8 k.y. periodicity with strong 1.2 m.y. modulations. These suggest a 22 h length of day and 1.2 m.y. interaction between the orbital inclinations of Earth and Mars. Comparing the 1.2 m.y. obliquity modulation cycles in these sections with Early Triassic records of global sea level, temperature, redox, and biotic evolution suggests that long-term astronomical forcing was involved in the repeated climatic and biotic upheavals that took place throughout the Early Triassic.

Obliquity Variability of a Potentially Habitable Early Venus

Obliquity Variability of a Potentially Habitable Early Venus

Authors:

Barnes et al

Abstract:

Venus currently rotates slowly, with its spin controlled by solid-body and atmospheric thermal tides. However, conditions may have been far different 4 billion years ago, when the Sun was fainter and most of the carbon within Venus could have been in solid form, implying a low-mass atmosphere. We investigate how the obliquity would have varied for a hypothetical rapidly rotating Early Venus. The obliquity variation structure of an ensemble of hypothetical Early Venuses is simpler than that Earth would have if it lacked its large moon (Lissauer et al., 2012), having just one primary chaotic regime at high prograde obliquities. We note an unexpected long-term variability of up to ±7° for retrograde Venuses.

Did the Tharsis Volcanic Eruptions Tilt Mars on its Axis During the Late Noachian/Early Hesperian?

Late Tharsis formation and implications for early Mars

Authors:

Bouley et al

Abstract:

The Tharsis region is the largest volcanic complex on Mars and in the Solar System. Young lava flows cover its surface (from the Amazonian period, less than 3 billion years ago) but its growth started during the Noachian era (more than 3.7 billion years ago). Its position has induced a reorientation of the planet with respect to its spin axis (true polar wander, TPW), which is responsible for the present equatorial position of the volcanic province. It has been suggested that the Tharsis load on the lithosphere influenced the orientation of the Noachian/Early Hesperian (more than 3.5 billion years ago) valley networks1 and therefore that most of the topography of Tharsis was completed before fluvial incision. Here we calculate the rotational figure of Mars (that is, its equilibrium shape) and its surface topography before Tharsis formed, when the spin axis of the planet was controlled by the difference in elevation between the northern and southern hemispheres (hemispheric dichotomy). We show that the observed directions of valley networks are also consistent with topographic gradients in this configuration and thus do not require the presence of the Tharsis load. Furthermore, the distribution of the valleys along a small circle tilted with respect to the equator is found to correspond to a southern-hemisphere latitudinal band in the pre-TPW geographical frame. Preferential accumulation of ice or water in a south tropical band is predicted by climate model simulations of early Mars applied to the pre-TPW topography. A late growth of Tharsis, contemporaneous with valley incision, has several implications for the early geological history of Mars, including the existence of glacial environments near the locations of the pre-TPW poles of rotation, and a possible link between volcanic outgassing from Tharsis and the stability of liquid water at the surface of Mars.

The Obliquity of Enceladus

The obliquity of Enceladus

Authors:

Baland et al

Abstract:

The extraordinary activity at Enceladus' warm south pole indicates the presence of an internal global or local reservoir of liquid water beneath the surface. While Tyler (2009, 2011) has suggested that the geological activity and the large heat flow of Enceladus could result from tidal heating triggered by a large obliquity of at least 0.05{\deg}-0.1{\deg}, theoretical models of the Cassini state predict the obliquity to be two to three orders of magnitude smaller for an entirely solid and rigid Enceladus. We investigate the influence of an internal subsurface ocean and of tidal deformations of the solid layers on the obliquity of Enceladus. Our Cassini state model takes into account the external torque exerted by Saturn on each layer of the satellite and the internal gravitational and pressure torques induced by the presence of the liquid layer. As a new feature, our model also includes additional torques that arise because of the periodic tides experienced by the satellite. We find that the upper limit for the obliquity of a solid Enceladus is 0.00045 degrees and is negligibly affected by elastic deformations. The presence of an internal ocean decreases this upper limit by 13.1%, elasticity attenuating this decrease by only 0.5%. Since the obliquity of Enceladus cannot reach Tyler's requirement, obliquity tides are unlikely to be the source of the large heat flow of Enceladus. More likely, the geological activity at Enceladus' south pole results from eccentricity tides. Even in the most favorable case, the upper limit for the obliquity of Enceladus corresponds to about two meters at most at the surface of Enceladus. This is well below the resolution of Cassini images. Control point calculations cannot be used to detect the obliquity of Enceladus, let alone to constrain its interior from an obliquity measurement.

The Earth did NOT Flip 90 degrees During the Ediacaran NeoProterozoic

A stable Ediacaran Earth recorded by single silicate crystals of the ca. 565 Ma Sept-Îles intrusion

Author:s:

Bono et al

Abstract:

The archetypical example of inertial interchange true polar wander (IITPW), the rapid rotation of the entire solid Earth by 90°, is based on two nearly orthogonal directions seen in paleomagnetic studies of the Sept-Îles (ca. 565 Ma) intrusion (Quebec, Canada). This motion has also been proposed as the driving force for the early Cambrian explosion of life. Others have challenged these interpretations, linking the data instead to flips between an axial and equatorial dipole field configuration. We examine this enigma using single silicate crystal paleomagnetic analyses. We conclude that only one of the previously reported magnetic directions is carried by single domain magnetic grains and can be considered primary. Thus, the Ediacaran diversification occurred on a rotationally stable Earth driven by biotic and longer term abiotic forcing. Whether IITPW ever occurred in the past on Earth remains uncertain.

Long Term Northern Hemisphere Glaciation on Mars in Middle to Late Amazonian

An extended period of episodic northern mid-latitude glaciation on Mars during the Middle to Late Amazonian: Implications for long-term obliquity history

Authors:

Fassett et al

Abstract:

Mars is the only planet other than Earth in the Solar System that has a preserved nonpolar geological record of glaciation on its surface. Nonpolar ice deposits on Mars have been linked to variations in spin-axis obliquity that cause mobilization of polar ice and redeposition at lower latitudes, forming ice-rich and glacial deposits. Remnant nonpolar glacial deposits are found across the northern mid-latitudes where surface ice is not currently stable, implying that different climatic conditions existed on Mars in the past. Individual glacial deposits are often too small to date reliably using impact crater size-frequency data. We describe a novel approach that allows us to derive new information about when glaciation occurred in broad areas of the northern mid-latitudes. In this region we have classified (1) craters that superpose preexisting glacial deposits and were modified by later accumulation (and therefore formed during an epoch when glaciation was occurring), and (2) craters that are superposed on glacial deposits but are themselves unmodified by ice accumulation (and thus post-date significant glaciation). The sparse population of post-glacial craters reveals that the last period of extensive ice deposition of this type in this latitude band was recent (Late Amazonian). The substantial number of craters formed during the recurring glacial periods implies that northern mid-latitude glaciation was a long-lived recurring process, occurring over a period of at least ∼600 m.y. On the basis of Mars atmospheric general circulation models, these results are consistent with higher obliquity being common in the past, with recurring periods of obliquity exceeding the 25° axial tilt of Mars today. These observations support the statistical prediction of J. Laskar and colleagues that the median obliquity during the Amazonian was ∼35°–40°.

The Stability and Habitability of a Moonless Earth

On the Spin-axis Dynamics of a Moonless Earth

Authors:

Li et al

Abstract:

The variation of a planet's obliquity is influenced by the existence of satellites with a high mass ratio. For instance, the Earth's obliquity is stabilized by the Moon, and would undergo chaotic variations in the Moon's absence. In turn, such variations can lead to large-scale changes in the atmospheric circulation, rendering spin-axis dynamics a central issue for understanding climate. The relevant quantity for dynamically-forced climate change is the rate of chaotic diffusion. Accordingly, here we reexamine the spin-axis evolution of a Moonless Earth within the context of a simplified perturbative framework. We present analytical estimates of the characteristic Lyapunov coefficient as well as the chaotic diffusion rate and demonstrate that even in absence of the Moon, the stochastic change in the Earth's obliquity is sufficiently slow to not preclude long-term habitability. Our calculations are consistent with published numerical experiments and illustrate the putative system's underlying dynamical structure in a simple and intuitive manner.