Chadwick Aaron Trujillo

Properties of the Trans-Neptunian Belt: Statistics from the Canada-France-Hawaii Telescope Survey*

We present the results of a wide-field survey designed to measure the size, inclination, and radial distributions of Kuiper Belt objects (KBOs). The survey found 86 KBOs in 73 deg2 observed to limiting red magnitude of 23.7 using the Canada-France-Hawaii Telescope and the 12K × 8K CCD mosaic camera. For the first time, both ecliptic and off-ecliptic fields were examined to more accurately constrain the inclination distribution of the KBOs. The survey data were processed using an automatic moving-object detection algorithm, allowing a careful characterization of the biases involved. In this work, we quantify fundamental parameters of the classical KBOs (CKBOs), the most numerous objects found in our sample, using the new data and a maximum likelihood simulation. Deriving results from our best-fit model, we find that the size distribution follows a differential power law with exponent q = 4.0 (1 σ, or 68.27% confidence). In addition, the CKBOs inhabit a very thick disk consistent with a Gaussian distribution of inclinations with a half-width of i1/2 = 20 deg (1 σ). We estimate that there are NCKBO(D > 100 km) = 3.8 × 104 (1 σ) CKBOs larger than 100 km in diameter. We also find compelling evidence for an outer edge to the CKBOs at heliocentric distances R = 50 AU.

DISCOVERY OF A CANDIDATE INNER OORT CLOUD PLANETOID

We report the discovery of the minor planet (90377) Sedna, the most distant object ever seen in the solar system. Prediscovery images from 2001, 2002, and 2003 have allowed us to refine the orbit sufficiently to conclude that Sedna is on a highly eccentric orbit that permanently resides well beyond the Kuiper Belt with a semimajor axis of 480 ± 40 AU and a perihelion of 76 ± 4 AU. Such an orbit is unexpected in our current understanding of the solar system but could be the result of scattering by a yet-to-be-discovered planet, perturbation by an anomalously close stellar encounter, or formation of the solar system within a cluster of stars. In all of these cases a significant additional population is likely present, and in the two most likely cases Sedna is best considered a member of the inner Oort Cloud, which then extends to much smaller semimajor axes than previously expected. Continued discovery and orbital characterization of objects in this inner Oort Cloud will verify the genesis of this unexpected population.

LARGE KUIPER BELT OBJECTS: THE MAUNA KEA 8K CCD SURVEY

We describe a large-area ecliptic survey designed to assess the sky-plane surface density of bright Kuiper Belt objects. We used an 8192 ) 8192 pixel CCD mosaic to image 51.5 deg2 to a 50% detection threshold red magnitude Thirteen new Kuiper Belt objects were identi—ed in the survey, m R \ 22.5. including some of the brightest and, presumably, largest known examples. We use Monte Carlo models to assess the eUects of observational bias in our survey and to examine (1) the size distribution of bright objects in the Kuiper Belt, (2) the possible existence of a cutoU in the size distribution at large radii, (3) the intrinsic ratio of Plutinos to nonresonant (ii classical ˇˇ) Kuiper Belt objects, (4) the intrinsic ratio of populations in the 3:2 and 2:1 mean motion resonances, and (5) the radial extent of the Kuiper Belt.

Discovery of a Planetary-sized Object in the Scattered Kuiper Belt

We present the discovery and initial physical and dynamical characterization of the object 2003 UB313. The object is sufficiently bright that for all reasonable values of the albedo it is certain to be larger than Pluto. Prediscovery observations back to 1989 are used to obtain an orbit with extremely small errors. The object is currently at aphelion in what appears to be a typical orbit for a scattered Kuiper Belt object, except that it is inclined by about 44° from the ecliptic. The presence of such a large object at this extreme inclination suggests that high-inclination Kuiper Belt objects formed preferentially closer to the Sun. Observations from Gemini Observatory show that the infrared spectrum is, like that of Pluto and 2005 FY9, dominated by the presence of frozen methane, although visible photometry shows that the object is almost neutral in color compared to Plutos extremely red color. 2003 UB313 is likely to undergo substantial seasonal change over the large range of heliocentric distances that it travels; at its current distance, Pluto is likely to prove a useful analog for better understanding the range of seasonal changes on this body.

A Correlation between Inclination and Color in the Classical Kuiper Belt

We have measured broadband optical BVR photometry of 24 classical and scattered Kuiper belt objects (KBOs), approximately doubling the published sample of colors for these classes of objects. We find a statistically significant correlation between object color and inclination in the classical Kuiper belt using our data. The color and inclination correlation increases in significance after the inclusion of additional data points culled from all published works. Apparently, this color and inclination correlation has not been more widely reported because the Plutinos show no such correlation and thus have been a major contaminant in previous samples. The color and inclination correlation excludes simple origins of color diversity, such as the presence of a coloring agent without regard to dynamical effects. Unfortunately, our current knowledge of the Kuiper belt precludes us from understanding whether the color and inclination trend is due to environmental factors, such as collisional resurfacing, or primordial population effects. A perihelion and color correlation is also evident, although this appears to be a spurious correlation induced by sampling bias, as perihelion and inclination are correlated in the observed sample of KBOs.

A Sedna-like body with a perihelion of 80 astronomical units

The observable Solar System can be divided into three distinct regions: the rocky terrestrial planets including the asteroids at 0.39 to 4.2 astronomical units (au) from the Sun (where 1 au is the mean distance between Earth and the Sun), the gas giant planets at 5 to 30 au from the Sun, and the icy Kuiper belt objects at 30 to 50 au from the Sun. The 1,000-kilometre-diameter dwarf planet Sedna was discovered ten years ago and was unique in that its closest approach to the Sun (perihelion) is 76 au, far greater than that of any other Solar System body. Formation models indicate that Sedna could be a link between the Kuiper belt objects and the hypothesized outer Oort cloud at around 10,000 au from the Sun. Here we report the presence of a second Sedna-like object, 2012 VP113, whose perihelion is 80 au. The detection of 2012 VP113 confirms that Sedna is not an isolated object; instead, both bodies may be members of the inner Oort cloud, whose objects could outnumber all other dynamically stable populations in the Solar System.

NEAR-INFRARED SPECTROSCOPY OF CHARON: POSSIBLE EVIDENCE FOR CRYOVOLCANISM ON KUIPER BELT OBJECTS

We present the first reported adaptive optics spectra of Charon in the H and K bands, which examine the anti-Pluto and sub-Pluto hemispheres. The ice temperature is estimated at 40-50 K, based on the 1.65 μm feature of crystalline water ice. We obtain the most accurate profiles of the 2.21 μm feature and confirm that the feature is due to hydrated ammonia. We attribute hemispheric differences in the features profile to different hydration states. We calculate the rate at which crystalline water ice is amorphized by solar UV/visible radiation, finding that at the depths probed by H and K observations (≈350 μm), the e-folding time to amorphize ice is (3-5) × 104 yr. This implies Charons ice crystallized from a melt, or has been heated to 90 K, during the last ~105 yr. The extent of the crystalline water ice and the short timescales involved argue that surface renewal is necessary, a conclusion reinforced by the presence of ammonia hydrates. We investigate possible mechanisms for surface renewal and conclude that cryovolcanism is the most likely.

A new dynamical class of object in the outer Solar System

Some three dozen objects have now been discovered beyond the orbit of Neptune and classified as members of the Kuiper belt—a remnant population of icy planetesimals that failed to be incorporated into planets. At still greater distances is believed to lie the Oort cloud—a massive population of cometary objects distributed approximately in a sphere of characteristic dimension 50,000au(ref. 6). Here we report the discovery of an object, 1996TL66, that appears to be representative of a population of scattered bodies located between the Kuiper belt and the Oort cloud. 1996TL66has an orbital semimajor axis of 84au, and is in an extremely eccentric and highly inclined orbit (e = 0.58, i = 24°). With a red magnitude ∼20.9, it is the brightest trans-neptunian object yet found since Pluto and Charon. Its discovery suggests that the Kuiper belt extends substantially beyond the 30–50auregion sampled by previous surveys, and may contain much more mass than previously suspected.

Population and Size Distribution of Small Jovian Trojan Asteroids

We present a study of Jovian Trojan objects detected serendipitously during the course of a sky survey conducted at the University of Hawaii 2.2 m telescope. We used a 8192 × 8192 pixel charge-coupled device (CCD) mosaic to observe 20 deg2 at locations spread over the L4 Lagrangian swarm and reached a limiting magnitude V = 22.5 (50% of maximum detection efficiency). Ninety-three Jovian Trojans were detected with radii 2 km ≤ r ≤ 20 km (assumed visual albedo 0.04). Their differential magnitude distribution has a slope of 0.40 ± 0.05, corresponding to a power-law size distribution index 3.0 ± 0.3 (1 σ). The total number of L4 Trojans with radii ≥1 km is of order 1.6 × 105, and their combined mass (dominated by the largest objects) is ~10-4 MEarth. The bias-corrected mean inclination is 137 ± 05. We also discuss the size and spatial distribution of the L4 swarm.

The Radial Distribution of the Kuiper Belt

We examine the radial distribution of the Kuiper Belt objects (KBOs) using a method that is insensitive to observational bias effects. This technique allows the use of the discovery distances of all KBOs, independent of orbital classification or discovery circumstance. We verify the presence of an outer edge to the Kuiper Belt, as reported in other works, and we measure this edge to be at R = 47 ± 1 AU given any physically plausible model of the size distribution. We confirm that this outer edge is due to the classical KBOs, the most numerically dominant observationally. In addition, we find that current surveys do not preclude the presence of a second, unobserved Kuiper Belt beyond R = 76 AU.