Aster G. Taylor

I am a graduate student in Astronomy at the University of Michigan, working with Fred Adams. I obtained my undergraduate degree in Astrophysics from the University of Chicago in 2023, where I worked primarily with Darryl Seligman.

I am a Fannie and John Hertz Fellow, a recipient of the Rackham Science Award, and a Michigan Institute for Computational Discovery and Engineering Fellow.

I primarily study theoretical and computational planetary science and astrophysics. Currently, I am working on the dynamics and accelerations of solar system small bodies, specifically on the origins of the mysterious accelerations of “dark comets”. I am also working on the radiative signatures of circumplanetary disks during giant planet formation. I am generally interested in fluid dynamics, minor bodies, planet formation, and plasma physics.

In my spare time, I like to hike, read science fiction (especially Ada Palmer and Iain Banks), play board games and Dungeons and Dragons, work out, and practice martial arts (Shaolin kempo and mixed martial arts).

I am also a citizen of the Muscogee (Creek) Nation of Oklahoma.

Please contact me at agtaylor@umich.edu for questions and collaborations.

selected publications

2024

Formation and structure of circumplanetary disks and envelopes during the late stages of giant planet formation

Aster G. Taylor, and Fred C. Adams

Icarus, Mar 2024

Abs

Giant planets are expected to form within circumplanetary disks, which shape their formation history and the local environment. Here, we consider the formation and structure of circumplanetary disks that arise during the late stages of giant planet formation. During this phase, when most of the final mass is accumulated, incoming material enters the Hill sphere and falls toward the planet. In the absence of torques, the falling parcels of gas conserve their specific angular momentum and collect into a circumplanetary disk. Generalizing previous work, we consider a range of possible geometries for the flow entering the sphere of influence of the planet. Specifically, we consider five geometric patterns for the inward flow, ranging from concentration toward the rotational poles of the system to isotropic flow to concentration along the equatorial plane. For each case, we derive analytic descriptions for the density field of the infall region, the disk surface density in the absence of viscosity, and steady-state solutions for viscous disks. These results, in turn, specify the luminosity contributions of the planet, the circumplanetary disk, and the envelope. These power sources, in conjunction with the surrounding material, collectively determine the observational appearance of the forming planet. We conclude with an approximate determination of these radiative signatures.

2023

Seasonally varying outgassing as an explanation for dark comet accelerations

Aster G. Taylor, Davide Farnocchia, David Vokrouhlický, and 3 more authors

Icarus, Oct 2023

Abs

Significant nonradial, nongravitational accelerations with magnitudes incompatible with radiation-driven effects have been reported in seven photometrically inactive near-Earth objects. Two of these objects exhibit large transverse accelerations (i.e., within the orbital plane but orthogonal to the radial direction), and six exhibit significant out-of-plane accelerations. Here, we find that anisotropic outgassing resulting from differential heating on a nucleus with nonzero spin-pole obliquity, averaged over an eccentric orbit, can explain these accelerations for most of the objects. This balanced outgassing model depends on three parameters — the spin pole orientation (R.A. and Dec.) and an acceleration magnitude. For these “dark comets” (excepting 2003 RM), we obtain parameter values that reproduce the observed nongravitational accelerations. We derive formulae for the component accelerations under certain assumptions for the acceleration scaling over heliocentric distance. Although we lack estimates of these objects’ spin axes to confirm our values, this mechanism is nevertheless a plausible explanation for the observed accelerations, and produces accurate perturbations to the heliocentric motions of most of these objects. This model may also be applied to active objects outside of the dark comets group.
Fitting the Light Curve of 1I/‘Oumuamua with a Nonprincipal Axis Rotational Model and Outgassing Torques

Aster G. Taylor, Darryl Z. Seligman, Olivier R. Hainaut, and 1 more author

The Planetary Science Journal, Oct 2023

Abs

In this paper, we investigate the nonprincipal axis (NPA) rotational state of 1I/‘Oumuamua—the first interstellar object discovered traversing the inner solar system—from its photometric light curve. Building upon Mashchenko, we develop a model which incorporates NPA rotation and Sun-induced, time-varying outgassing torques to generate synthetic light curves of the object. The model neglects tidal forces, which are negligible compared to outgassing torques over the distances at which ‘Oumuamua was observed. We implement an optimization scheme that incorporates the NPA rotation model to calculate the initial rotation state of the object. We find that an NPA rotation state with an average period of 〈P〉 ≃ 7.34 hr best reproduces the photometric data. The discrepancy between this period and previous estimates is due to continuous period modulation induced by outgassing torques in the rotational model, as well as different periods being used. The best fit to the 2017 October data does not reproduce the 2017 November data (although the later measurements are too sparse to fit). The light curve is consistent with there being no secular evolution of the angular momentum, which is somewhat in tension with the empirical correlations between nuclear spin-up and cometary outgassing. The complex rotation of ‘Oumuamua may be the result of primordial rotation about the smallest principal axis if (i) the object experienced hypervolatile outgassing and (ii) our idealized outgassing model is accurate.
Interstellar Comets from Post-main-sequence Systems as Tracers of Extrasolar Oort Clouds

W. Garrett Levine, Aster G. Taylor, Darryl Z. Seligman, and 4 more authors

Planetary Science Journal, Jul 2023
Numerical Simulations of Tidal Deformation and Resulting Light Curves of Small Bodies: Material Constraints of 99942 Apophis and 1I/’Oumuamua

Aster G. Taylor, Darryl Z. Seligman, Douglas R. MacAyeal, and 2 more authors

Planetary Science Journal, May 2023