The Smallest Particles in Saturn's A and C Rings

Radio occultations of Saturn's main rings by spacecraft suggest a power law particle size-distribution down to sizes of the order of 1 cm (Marouf et al., 1983), (Zebker et al., 1985). The lack of optical depth variations between ultraviolet and near-IR wavelengths indicate a lack of micron-sized particles. Between these two regimes, the particle-size distribution is largely unknown. A cutoff where the particle-size distribution turns over must exist, but the position and shape of it is not clear from existing studies. Using a series of solar occultations performed by the VIMS instrument on-board Cassini in the near-infrared, we are able to measure light forward scattered by particles in the A and C rings. With a model of diffraction by ring particles, and the previous radio work as a constraint on the slope of the particle size distribution, we estimate the minimum particle size using a truncated power-law size distribution. The C Ring shows a minimum particle size of $4.1^{+3.8}_{-1.3}$ mm, with an assumed power law index of q=3.1 and a maximum particle size of 10 m. The A Ring signal shows a similar level of scattered flux, but modeling is complicated by the presence of self-gravity wakes and higher optical depths. If q<3, our A Ring model requires a minimum particle size below one millimeter (< 0.34 mm for an assumed q=2.75, or $0.56^{+0.35}_{-0.16}$ mm for a steeper q=2.9) to be consistent with VIMS observations. These results might seem to contradict previous optical(Dones et al., 1993) and infrared (French and Nicholson, 2000) work, which implied that there were few particles in the A Ring smaller than 1 cm. But, because of the shallow power law, relatively little optical depth (between 0.03 and 0.16 in extinction, or 0.015 - 0.08 in absorption) is provided by these particles.Comment: 47 pages, 16 figures, 3 Table

Non-circular features in Saturn's D ring: D68

D68 is a narrow ringlet located only 67,627 km (1.12 planetary radii) from Saturn's spin axis. Images of this ringlet obtained by the Cassini spacecraft reveal that this ringlet exhibits persistent longitudinal brightness variations and a substantial eccentricity (ae=25+/-1 km). By comparing observations made at different times, we confirm that the brightness variations revolve around the planet at approximately the local orbital rate (1751.6 degrees/day), and that the ringlet's pericenter precesses at 38.243+/-0.008 degrees/day, consistent with the expected apsidal precession rate at this location due to Saturn's higher-order gravitational harmonics. Surprisingly, we also find that the ringlet's semi-major axis appears to be decreasing with time at a rate of 2.4+/-0.4 km/year between 2005 and 2013. A closer look at these measurements, along with a consideration of earlier Voyager observations of this same ringlet, suggests that the mean radius of D68 moves back and forth, perhaps with a period of around 15 Earth years or about half a Saturn year. These observations could place important constraints on both the ringlet's local dynamical environment and the planet's gravitational field.Comment: 39 Pages, 11 Figures accepted for publication in Icarus Text slightly modified to match corrections to proof

LASR-Guided Stellar Photometric Variability Subtraction: The Linear Algorithm For Significance Reduction

We develop a technique for removing stellar variability in the light curves of $\delta$-Scuti and similar stars. Our technique, which we name the Linear Algorithm for Significance Reduction (LASR), subtracts oscillations from a time series by minimizing their statistical significance in frequency space. We demonstrate that LASR can subtract variable signals of near-arbitrary complexity and can robustly handle close frequency pairs and overtone frequencies. We demonstrate that our algorithm performs an equivalent fit as prewhitening to the straightforward variable signal of KIC 9700322. We also show that LASR provides a better fit to seismic activity than prewhitening in the case of the complex $\delta$-Scuti KOI-976.Comment: 9 pages, 5 figures, accepted for publication in Astronomy & Astrophysics. Pseudocode and github link to code included in manuscrip

The Science Project Portfolio

The phrase science fair project likely conjures up images of students working independently on smoldering model volcanoes, catapults, and Rube Goldberg contraptions. To create their projects, students and teachers blindly follow a set of seemingly incomprehensible steps, assembling various pieces. This process continues until the due date arrives, when all the pieces are packaged up for the science fair. Teachers are then expected to assess all the projects in a timely manner while somehow continuing to deliver their curriculum. Eventually, the student receives feedback and, often, a semester-making grade. By that time, everyone is exhausted and relieved it’s over