Limits on Pluto’s ring system from the June 12 2006 stellar occultation and implications for the New Horizons impact hazard

The Pluto system passed in front of a 15th magnitude star on 12 June 2006. We observed this occultation from the 3.9 m Anglo-Australian Telescope (AAT), and took photometric observations every 100 ms for 3 h. Our three-hour baseline of data provides among the longest and highest-quality occultation dataset of the Pluto system ever taken. Results on Pluto’s atmospheric structure from these data have been previously reported (Young, E.F. [2008]. Astron. J. 136, 1757–1769). Here we report on limits for rings, ring arcs, and small satellites within the system. We find a 3σ3σ upper limit on the normal optical depth of τ<0.07τ<0.07 for narrow rings of width 2.4 km, and τ<5×10-3τ<5×10-3 for rings of width 1500 km. We also detect no discrete objects of radius 220 m or larger along the occultation path. Motivated by the upcoming flyby of New Horizons through the Pluto system, we estimate the dust impact hazard to the spacecraft based on our optical depth limits and those derived from imaging with the Hubble Space Telescope.http://www.elsevier.com/locate/icarushb201

Physical Characterization of TNOs with the James Webb Space Telescope

International audienc

Ralph: A Visible/Infrared Imager for the New Horizons Pluto/Kuiper Belt Mission

The New Horizons instrument named Ralph is a visible/near infrared multi-spectral imager and a short wavelength infrared spectral imager. It is one of the core instruments on New Horizons, NASA's first mission to the Pluto/Charon system and the Kuiper Belt. Ralph combines panchromatic and color imaging capabilities with IR imaging spectroscopy. Its primary purpose is to map the surface geology and composition of these objects, but it will also be used for atmospheric studies and to map the surface temperature. It is a compact, low-mass (10.5 kg), power efficient (7.1 W peak), and robust instrument with good sensitivity and excellent imaging characteristics. Other than a door opened once in flight, it has no moving parts. These characteristics and its high degree of redundancy make Ralph ideally suited to this long-duration flyby reconnaissance mission.Comment: 18 pages, 15 figures, 4 tables; To appear in a special volume of Space Science Reviews on the New Horizons missio

A statistical review of light curves and the prevalence of contact binaries in the Kuiper Belt

We investigate what can be learned about a population of distant Kuiper Belt Objects (KBOs) by studying the statistical properties of their light curves. Whereas others have successfully inferred the properties of individual, highly variable KBOs, we show that the fraction of KBOs with low amplitudes also provides fundamental information about a population. Each light curve is primarily the result of two factors: shape and orientation. We consider contact binaries and ellipsoidal shapes, with and without flattening. After developing the mathematical framework, we apply it to the existing body of KBO light curve data. Principal conclusions are as follows. (1) When using absolute magnitude H as a proxy for the sizes of KBOs, it is more accurate to use the maximum of the light curve (minimum H) rather than the mean. (2) Previous investigators have noted that smaller KBOs tend to have higher-amplitude light curves, and have interpreted this as evidence that they are systematically more irregular in shape than larger KBOs; we show that a population of flattened bodies with uniform proportions, independent of size, could also explain this result. (3) Our method of analysis indicates that prior assessments of the fraction of contact binaries in the Kuiper Belt may be artificially low. (4) The pole orientations of some KBOs can be inferred from observed changes in their light curves over time scales of decades; however, we show that these KBOs constitute a biased sample, whose pole orientations are not representative of the population overall. (5) Although surface topography, albedo patterns, limb darkening, and other surface properties can affect individual light curves, they do not have a strong influence on the statistics overall. (6) Photometry from the Outer Solar System Origins Survey (OSSOS) survey is incompatible with previous results and its statistical properties defy easy interpretation. We also discuss the promise of this approach for the analysis of future, much larger data sets such as the one anticipated from the upcoming Vera C. Rubin Observatory