BYU Physics and Astronomy

We present and discuss five candidate exoplanetary systems identified with the Kepler spacecraft. These five systems show transits from multiple exoplanet candidates. Should these objects prove to be planetary in nature, then these five systems open new opportunities for the field of exoplanets and provide new insights into the formation and dynamical evolution of planetary systems. We discuss the methods used to identify multiple transiting objects from the Kepler photometry as well as the false-positive rejection methods that have been applied to these data. One system shows transits from three distinct objects while the remaining four systems show transits from two objects. Three systems have planet candidates that are near mean motion commensurabilities-two near 2:1 and one just outside 5:2. We discuss the implications that multi-transiting systems have on the distribution of orbital inclinations in planetary systems, and hence their dynamical histories, as well as their likely masses and chemical compositions. A Monte Carlo study indicates that, with additional data, most of these systems should exhibit detectable transit timing variations (TTVs) due to gravitational interactions, though none are apparent in these data. We also discuss new challenges that arise in TTV analyses due to the presence of more than two planets in a system.

The Kepler spacecraft is monitoring more than 150,000 stars for evidence of planets transiting those stars. We report the detection of two Saturn-size planets that transit the same Sun-like star, based on 7 months of Kepler observations. Their 19.2- and 38.9-day periods are presently increasing and decreasing at respective average rates of 4 and 39 minutes per orbit; in addition, the transit times of the inner body display an alternating variation of smaller amplitude. These signatures are characteristic of gravitational interaction of two planets near a 2: 1 orbital resonance. Six radial-velocity observations show that these two planets are the most massive objects orbiting close to the star and substantially improve the estimates of their masses. After removing the signal of the two confirmed giant planets, we identified an additional transiting super-Earth-size planet candidate with a period of 1.6 days.

We present the results of a wide-field survey using the 1.2 m Samuel Oschin Telescope at Palomar Observatory. This survey was designed to find the most distant members of the Kuiper Belt and beyond. We searched similar to 12,000 deg(2) down to a mean limiting magnitude of 21.3 in R. A total number of 52 Kuiper Belt objects and Centaurs have been detected, 25 of which were discovered in this survey. Except for the redetection of Sedna, no additional Sedna-like bodies with perihelia greater than 45 AU were detected despite sensitivity out to distances of 1000 AU. We discuss the implications for a distant Sedna-like population beyond the Kuiper Belt, focusing on the constraints we can place on the embedded stellar cluster environment the early Sun may be have been born in, where the location and distribution of Sedna-like orbits sculpted by multiple stellar encounters is indicative of the birth cluster size. We also report our observed latitude distribution and implications for the size of the plutino population.

Many binary minor planets (BMPs; both binary asteroids and binary trans-Neptunian objects) are known to exist in the solar system. The currently observed orbital and physical properties of BMPs hold essential information and clues about their origin, their evolution, and the conditions under which they evolved. Here, we study the orbital properties of BMPs with currently known mutual orbits. We find that BMPs are typically highly inclined relative to their orbit around the Sun, with a distribution consistent with an isotropic distribution. BMPs not affected by tidal forces are found to have high eccentricities with non-thermal eccentricity distribution peaking at intermediate eccentricities (typically 0.4-0.6). The high inclinations and eccentricities of the BMPs suggest that BMPs evolved in a dense collisional environment, in which gravitational encounters in addition to tidal and secular Kozai effects played an important role in their orbital evolution.

The Kuiper belt is a collection of small bodies (Kuiper belt objects, KBOs) that lie beyond the orbit of Neptune and which are believed to have formed contemporaneously with the planets. Their small size and great distance make them difficult to study. KBO 55636 (2002 TX(300)) is a member of the water-ice-rich Haumea KBO collisional family(1). The Haumea family are among the most highly reflective objects in the Solar System. Dynamical calculations indicate that the collision that created KBO 55636 occurred at least 1 Gyr ago(2,3). Here we report observations of a multi-chord stellar occultation by KBO 55636, which occurred on 9 October 2009 UT. We find that it has a mean radius of 143 +/- 65 km (assuming a circular solution). Allowing for possible elliptical shapes, we find a geometric albedo of 0.88(0.06)(+0.15) in the V photometric band, which establishes that KBO 55636 is smaller than previously thought and that, like its parent body, it is highly reflective. The dynamical age implies either that KBO 55636 has an active resurfacing mechanism, or that fresh water-ice in the outer Solar System can persist for gigayear timescales.

The Kuiper Belt object (KBO) Orcus and its satellite Vanth form an unusual system in the Kuiper Belt. While most large KBOs have small satellites in circular orbits and smaller KBOs and their satellites tend to be much closer in size, Orcus sits in between these two regimes. Orcus is among the largest objects known in the Kuiper Belt, but the relative size of Vanth is much larger than that of the tiny satellites of the other large objects. Here, we characterize the physical and orbital characteristics of the Orcus-Vanth system in an attempt to distinguish discuss possible formation scenarios. From Hubble Space Telescope observations, we find that Orcus and Vanth have different visible colors and that Vanth does not share the water ice absorption feature seen in the infrared spectrum of Orcus. We also find that Vanth has a nearly face-on circular orbit with a period of 9.5393 +/- 0.0001 days and semimajor axis of 8980 +/- 20 km, implying a system mass of (6.32 +/- 0.01) x 10(20) kg or 3.8% the mass of dwarf planet Eris. From Spitzer Space Telescope observations, we find that the thermal emission is consistent with a single body with diameter 940 +/- 70 km and a geometric albedo of 0.28 +/- 0.04. Assuming equal densities and albedos, this measurement implies sizes of Orcus and Vanth of 900 and 280 km, respectively, and a mass ratio of 33. Assuming a factor of 2 lower albedo for the non-icy Vanth, however, implies sizes of 860 km and 380 km and a mass ratio of 12. The measured density depends on the assumed albedo ratio of the two objects but is approximately 1.5 +/- 0.3 g cm(-3), midway between typical densities measured for larger and smaller objects. The orbit and mass ratio is consistent with formation from a giant impact and subsequent outward tidal evolution, and even consistent with the system having now achieved a double synchronous state. Because of the large angle between the plane of the heliocentric orbit of Orcus and the plane of the orbit of Vanth, the system can be equally well explained, however, by initial eccentric capture, Kozai cycling to increase the eccentricity and decrease the pericenter of the orbit of Vanth, and subsequent inward tidal evolution. We discuss implications of these formation mechanisms.