Can Uranus’s Rings Reveal the Planet’s Deepest Secrets?

Planetary rings can act as seismometers that respond to changes deep within a planet.

An eccentric wave in the circumstellar disc of the Be/X-ray binary X Persei

ABSTRACT We present spectroscopic observations of the Be/X-ray binary X Per obtained during the period 2017 December–2020 January (MJD 58095–58865). In 2017 December, the H α, H β, and He i 6678 emission lines were symmetric with violet-to-red peak ratio V/R ≈ 1. During the first part of the period (2017 December–2018 August), the V/R ratio decreased to 0.5 and the asymmetry developed simultaneously in all three lines. In 2018 September, a third component with velocity ≈250 km s−1 appeared on the red side of the He i line profile. Later, this component emerged in H β, accompanied by the appearance of a red shoulder in H α. Assuming that it is due to an eccentric wave in the circumstellar disc, we find that the eccentric wave appeared first in the innermost part of the disc, it spreads out with outflowing velocity vwave ≈ 1.1 ± 0.2 km s−1, and the eccentricity of the eccentric wave is ewave ≈ 0.29 ± 0.07. A detailed understanding of the origin of such eccentricities would have applications to a wide range of systems from planetary rings to AGNs.

Possible case of exoplanetary rings around HIP 41378 f

<p>Planetary rings are exciting features yet to be detected around exoplanets despite their prevalence around the giant planets and other rocky bodies of the solar system. A number of studies have proposed methods to identify and characterise the signatures of rings mostly from transit light curves. Probing for the presence of rings in transit light curves is very useful as the rings can cause a number of effects both on the light curve shape and the inferred parameters of the planet.</p> <p>The presence of rings around a transiting planet can cause it to appear larger and lead to an underestimation of its density if the mass is known. Therefore, a class of planets with extremely low densities, called Super puffs, can be planets with yet undetected rings. A Bayesian framework is employed here to show that the anomalously low density (~0.09 g/cm<sup>3</sup>) of the transiting long-period planet HIP 41378f might be due to the presence of opaque circum-planetary rings. Analysing the light curve data from the K2 mission, we construct physically motivated model priors and found that the statistical evidence for the ringed planet scenario is  comparable to that of the planet-only scenario. The ringed planet solution suggests a larger planetary density of ~1.23 g/cm<sup>3</sup> similar to Uranus. The associated ring extends from 1.05 to 2.59 times the planetary radius and is inclined away from the sky-plane by ~25 degrees. However, the computed ring material density is lower than is expected for a planet with an equilibrium temperature of 294K so future high-precision transit observations of HIP 41378f would be necessary to confirm/dismiss the presence of planetary rings.</p>

Can planetary rings explain the extremely low density of HIP 41378 𝑓?

The presence of rings around a transiting planet can cause its radius to be overestimated and lead to an underestimation of its density if the mass is known. We employed a Bayesian framework to show that the anomalously low density (∼0.09 g cm−3) of the transiting long-period planet HIP 41378 𝑓 might be due to the presence of opaque circum-planetary rings. Given our adopted model priors and data from the K2 mission, we find the statistical evidence for the ringed planet scenario to be comparable to that of the planet-only scenario. The ringed planet solution suggests a larger planetary density of ∼1.23 g cm−3 similar to Uranus. The associated ring extends from 1.05 to 2.59 times the planetary radius and is inclined away from the sky plane by ∼25°. Future high-precision transit observations of HIP 41378 𝑓 would be necessary to confirm/dismiss the presence of planetary rings.

Multi-particle collisions in microgravity: Coefficient of restitution and sticking threshold for systems of mm-sized particles

Context. The current model of planet formation lacks a good understanding of the growth of dust particles inside the protoplanetary disk beyond mm sizes. A similar collisional regime exists in dense planetary rings. In order to investigate the low-velocity collisions between this type of particles, the NanoRocks experiment was flown on the International Space Station (ISS) between September 2014 and March 2016. We present the results of this experiment. Aims. The objectives of our data analysis are the quantification of the damping of energy in systems of multiple particles in the 0.1–1 mm size range while they are in the bouncing regime, and the study of the formation of clusters through sticking collisions between particles. Methods. We developed statistical methods for the analysis of the large quantity of collision data collected by the experiment. We measured the average motion of particles, the moment of clustering, and the cluster size formed. In addition, we ran simple numerical simulations in order to validate our measurements. Results. We computed the average coefficient of restitution (COR) of collisions and find values ranging from 0.55 for systems including a population of fine grains to 0.94 for systems of denser particles. We also measured the sticking threshold velocities and find values around 1 cm s−1, consistent with the current dust collision models based on independently collected experimental data. Conclusions. Our findings have the following implications that can be useful for the simulation of particles in PPDs and planetary rings: (1) The average COR of collisions between same-sized free-floating particles at low speeds (<2 cm s−1) is not dependent on the collision velocity; (2) The simplified approach of using a constant COR value will accurately reproduce the average behavior of a particle system during collisional cooling; (3) At speeds below 5 mm s−1, the influence of particle rotation becomes apparent on the collision behavior; (4) Current dust collision models predicting sticking thresholds are robust.