arXiv subjects

Zeeve Rogoszinski

Publications and source records attributed to Zeeve Rogoszinski.

4 recordsLinked to original sources

arXiv2022

Tilting Uranus via the migration of an ancient satellite

Context. The 98°-obliquity of Uranus is commonly attributed to giant impacts that occurred at the end of the planetary formation. This picture, however, is not devoid of weaknesses. Aims. On a billion-year timescale, the tidal migration of the satellites of Jupiter and Saturn has been shown to strongly affect their spin-axis dynamics. We aim to revisit the scenario of tilting Uranus in light of this mechanism. Methods. We analyse the precession spectrum of Uranus and identify the candidate secular spin-orbit resonances that could be responsible for the tilting. We determine the properties of the hypothetical ancient satellite required for a capture and explore the dynamics numerically. Results. If it migrates over 10 Uranus' radii, a single satellite with minimum mass 4e-4 Uranus' mass is able to tilt Uranus from a small obliquity and make it converge towards 90°. In order to achieve the tilting in less than the age of the Solar System, the mean drift rate of the satellite must be comparable to the Moon's current orbital expansion. Under these conditions, simulations show that Uranus is readily tilted over 80°. Beyond this point, the satellite is strongly destabilised and triggers a phase of chaotic motion for the planet's spin axis. The chaotic phase ends when the satellite collides into the planet, ultimately freezing the planet's obliquity in either a prograde, or plainly retrograde state (as Uranus today). Spin states resembling that of Uranus can be obtained with probabilities as large as 80%, but a bigger satellite is favoured, with mass 1.7e-3 Uranus' mass or more. Yet, a smaller ancient satellite is not categorically ruled out, and there is room for improving this basic scenario in future studies. Interactions among several pre-existing satellites is a promising possibility.

astro-ph.EP↗

arXiv2021

Tilting Uranus: Collisions versus Spin--Orbit Resonance

In this paper, we investigate whether Uranus's 98$^{\circ}$ obliquity was a by-product of a secular spin-orbit resonance assuming that the planet originated closer to the Sun. In this position, Uranus's spin precession frequency is fast enough to resonate with another planet located beyond Saturn. Using numerical integration, we show that resonance capture is possible in a variety of past solar system configurations, but that the timescale required to tilt the planet to 90$^{\circ}$ is of the order $\sim\!10^{8}$ yr -- a timespan that is uncomfortably long. A resonance kick could tilt the planet to a significant 40$^{\circ}$ in $\sim\!10^{7}$ yr only if conditions were ideal. We also revisit the collisional hypothesis for the origin of Uranus's large obliquity. We consider multiple impacts with a new collisional code that builds up a planet by summing the angular momentum imparted from impactors. Because gas accretion imparts an unknown but likely large part of the planet's spin angular momentum, we compare different collisional models for tilted, untilted, spinning, and nonspinning planets. We find that a 1 $M_{\oplus}$ strike is sufficient to explain the planet's current spin state, but that two $0.5\,M_{\oplus}$ collisions produce better likelihoods. Finally, we investigate hybrid models and show that resonances must produce a tilt of at least $\sim\!40^{\circ}$ for any noticeable improvements to the collision model. Because it is difficult for spin-orbit resonances to drive Uranus's obliquity to 98$^{\circ}$ even under these ideal conditions, giant impacts seem inescapable.

astro-ph.EP↗

arXiv2020

Tilting Ice Giants with a Spin-Orbit Resonance

Giant collisions can account for Uranus's and Neptune's large obliquities, yet generating two planets with widely different tilts and strikingly similar spin rates is a low-probability event. Trapping into a secular spin-orbit resonance, a coupling between spin and orbit precession frequencies, is a promising alternative, as it can tilt the planet without altering its spin period. We show with numerical integrations that if Uranus harbored a massive circumplanetary disk at least three times the mass of its satellite system while it was accreting its gaseous atmosphere, then its spin precession rate would increase enough to resonate with its own orbit, potentially driving the planet's obliquity to 70${^\circ}$. We find that the presence of a massive disk moves the Laplace radius significantly outward from its classical value, resulting in more of the disk contributing to the planet's pole precession. Although we can generate tilts greater than 70${^\circ}$ only rarely and cannot drive tilts beyond 90${^\circ}$, a subsequent collision with an object about $0.5\,M_{\oplus}$ could tilt Uranus from 70${^\circ}$ to 98${^\circ}$. Minimizing the masses and number of giant impactors from two or more to just one increases the likelihood of producing Uranus's spin states by about an order of magnitude. Neptune, by contrast, needs a less massive disk to explain its 30${^\circ}$ tilt, eliminating the need for giant collisions altogether.

astro-ph.EP↗

arXiv2020

The Brute-Force Search for Planet Nine

A recent proposal for the detection of a hypothetical gravitating body 500 AU from the Sun (termed Planet 9) calls for a fleet of near-relativistic spacecraft, equipped with high-precision clocks, to be sent to a region where the object is suspected to be. We show that the technological constraints of such a mission can be relaxed somewhat, while improving the sensitivity: high-precision clocks can be avoided when the transverse displacement induced by Planet 9 is measurable with Earth-based, or near-Earth, telescopes. Furthermore, we note that in the absence of Planet 9, these spacecraft still yield useful data by mapping gravitational perturbations in the outer parts of the solar system.

astro-ph.EP↗