Transformation of Trojans into Quasi-Satellites During Planetary Migration and Their Subsequent Close-Encounters with the Host Planet

We use numerical integrations to investigate the dynamical evolution of resonant Trojan and quasi-satellite companions during the late stages of migration of the giant planets Jupiter, Saturn, Uranus, and Neptune. Our migration simulations begin with Jupiter and Saturn on orbits already well separated from their mutual 2:1 mean-motion resonance. Neptune and Uranus are decoupled from each other and have orbital eccentricities damped to near their current values. From this point we adopt a planet migration model in which the migration speed decreases exponentially with a characteristic timescale tau (the e-folding time). We perform a series of numerical simulations, each involving the migrating giant planets plus test particle Trojans and quasi-satellites. We find that the libration frequencies of Trojans are similar to those of quasi-satellites. This similarity enables a dynamical exchange of objects back and forth between the Trojan and quasi-satellite resonances during planetary migration. Furthermore, under the influence of these secondary resonances quasi-satellites can have their libration amplitudes enlarged until they undergo a close-encounter with their host planet and escape from the resonance. High-resolution simulations of this escape process reveal that ~80% of Jovian quasi-satellites experience one or more close-encounters within Jupiter's Hill radius (R_H) as they are forced out of the quasi-satellite resonance. As many as ~20% come within R_H/4 and ~2.5% come within R_H/10. Close-encounters of escaping quasi-satellites occur near or even below the 2-body escape velocity from the host planet

Survival of Trojan-Type Companions of Neptune During Primordial Planet Migration

We investigate the survivability of Trojan-type companions of Neptune during primordial radial migration of the giant planets Jupiter, Saturn, Uranus, and Neptune. Loss of Neptune Trojans during planetary migration is not a random diffusion process. Rather, losses occur almost exclusively during discrete episodes when Trojan particles are swept by secondary resonances associated with mean-motion commensurabilities of Uranus with Neptune. The single greatest episode of loss ejects nearly 75% of existing Neptune Trojans and occurs just prior to Neptune reaching its final orbit.Comment: LaTeX file, 26 total pages with 1 table and 11 eps figures. Submitted to Icaru

Blending Entertainment, Education, and Science in a Modern Digital Planetarium

Students at the University of Arizona have a relatively rare opportunity to learn in a state-of-the-art planetarium. Originally opened as a campus planetarium in 1975, the Flandrau Science Center recently expanded into the digital realm. In 2014 Flandrau’s antique Minolta star projector was joined by a full-dome 4K digital projection system powered by a high performance computer cluster. Currently three science courses are taught in the planetarium for non-science majors — stellar astronomy, astrobiology, and planetary science (taught by SJK).The new digital system allows us to take our classes off the surface of Earth on a journey into the cosmos. Databases from dozens of spacecraft missions and deep-space telescopic surveys are tapped by the software to generate a realistic immersive 3D perspective of the universe, from local planets, satellites and rings to distant stars and galaxies all the way out to the limit of the visible universe. Simple clicks of a mouse allow us to change the orientation, trajectory, and speed of the virtual spacecraft, giving our students diverse views of different phenomena.The challenge with this system is harnessing the entertainment aspect for educational purposes. The visualization capabilities allow us to artificially enhance certain features and time scales. For example, the sizes of Earth and the moon can be enlarged on-the-fly to help demonstrate phases and eclipses. Polar axes and latitude lines can be added to Earth as it orbits the sun to help convey the reasons for seasons. Orbital paths can be highlighted to allow students to more accurately comprehend the population of near-Earth asteroids.These new immersive computer-generated visualization techniques have the potential to enhance comprehension in science education, especially for concepts involving 3D spatial and temporal relationships. Whether or not this potential is being realized will require studies to gauge student learning and retention beyond the short-term semester-long course. This work is just beginning