Rotation-stimulated structures in the CN and C3 comae of comet 103P/Hartley 2 around the EPOXI encounter

In late 2010 a Jupiter Family comet 103P/Hartley 2 was a subject of an intensive world-wide investigation. On UT October 20.7 the comet approached the Earth within only 0.12 AU, and on UT November 4.6 it was visited by NASA's EPOXI spacecraft. We joined this international effort and organized an observing campaign. The images of the comet were obtained through narrowband filters using the 2-m telescope of the Rozhen National Astronomical Observatory. They were taken during 4 nights around the moment of the EPOXI encounter. Image processing methods and periodicity analysis techniques were used to reveal transient coma structures and investigate their repeatability and kinematics. We observe shells, arc-, jet- and spiral-like patterns, very similar for the CN and C3 comae. The CN features expanded outwards with the sky-plane projected velocities between 0.1 to 0.3 km/s. A corkscrew structure, observed on November 6, evolved with a much higher velocity of 0.66 km/s. Photometry of the inner coma of CN shows variability with a period of 18.32+/-0.30 h (valid for the middle moment of our run, UT 2010 Nov. 5.0835), which we attribute to the nucleus rotation. This result is fully consistent with independent determinations around the same time by other teams. The pattern of repeatability is, however, not perfect, which is understendable given the suggested excitation of the rotation state, and the variability detected in CN correlates well with the cyclic changes in HCN, but only in the active phases. The revealed coma structures, along with the snapshot of the nucleus orientation obtained by EPOXI, let us estimate the spin axis orientation. We obtained RA=122 deg, Dec=+16 deg (epoch J2000.0), neglecting at this point the rotational excitation.Comment: 9 pages, 10 figures, submitted to Astron. Astrophy

Spitzer Space Telescope Observations of the Nucleus of Comet 103P/Hartley 2

We have used the Spitzer Space Telescope InfraRed Spectrograph (IRS) 22-μm peakup array to observe thermal emission from the nucleus and trail of comet 103P/Hartley 2, the target of NASA’s Deep Impact Extended Investigation (DIXI). The comet was observed on UT 2008 August 12 and 13, while 5.5 AU from the Sun. We obtained two 200 frame sets of photometric imaging over a 2.7 hr period. To within the errors of the measurement, we find no detection of any temporal variation between the two images. The comet showed extended emission beyond a point source in the form of a faint trail directed along the comet’s antivelocity vector. After modeling and removing the trail emission, a NEATM model for the nuclear emission with beaming parameter of 0.95 ± 0.20 indicates a small effective radius for the nucleus of 0.57 ± 0.08 km and low geometric albedo 0.028 ± 0.009 (1σ). With this nucleus size and a water production rate of 3 × 10^(28) molecules s^(-1) at perihelion, we estimate that ~100% of the surface area is actively emitting volatile material at perihelion. Reports of emission activity out to ~5 AU support our finding of a highly active nuclear surface. Compared to Deep Impact’s first target, comet 9P/Tempel 1, Hartley 2’s nucleus is one-fifth as wide (and about one-hundredth the mass) while producing a similar amount of outgassing at perihelion with about 13 times the active surface fraction. Unlike Tempel 1, comet Hartley 2 should be highly susceptible to jet driven spin-up torques, and so could be rotating at a much higher frequency. Since the amplitude of nongravitational forces are surprisingly similar for both comets, close to the ensemble average for ecliptic comets, we conclude that comet Hartley 2 must have a much more isotropic pattern of time-averaged outgassing from its nuclear surface. Barring a catastrophic breakup or major fragmentation event, the comet should be able to survive up to another 100 apparitions (~700 yr) at its current rate of mass loss

The yeast genome undergoes significant topological reorganization in quiescence

We have examined the three-dimensional organization of the yeast genome during quiescence by a chromosome capture technique as a means of understanding how genome organization changes during development. For exponentially growing cells we observe high levels of inter-centromeric interaction but otherwise a predominance of intrachromosomal interactions over interchromosomal interactions, consistent with aggregation of centromeres at the spindle pole body and compartmentalization of individual chromosomes within the nucleoplasm. Three major changes occur in the organization of the quiescent cell genome. First, intrachromosomal associations increase at longer distances in quiescence as compared to growing cells. This suggests that chromosomes undergo condensation in quiescence, which we confirmed by microscopy by measurement of the intrachromosomal distances between two sites on one chromosome. This compaction in quiescence requires the condensin complex. Second, inter-centromeric interactions decrease, consistent with prior data indicating that centromeres disperse along an array of microtubules during quiescence. Third, inter-telomeric interactions significantly increase in quiescence, an observation also confirmed by direct measurement. Thus, survival during quiescence is associated with substantial topological reorganization of the genome

Explosion of Comet 17P/Holmes as revealed by the Spitzer Space Telescope

An explosion on comet 17P/Holmes occurred on 2007 Oct 23, projecting particulate debris of a wide range of sizes into the interplanetary medium. We observed the comet using the Spitzer spectrograph on 2007 Nov 10 and 2008 Feb 27, and the photometer, on 2008 Mar 13. The fresh ejecta have detailed mineralogical features from small crystalline silicate grains. The 2008 Feb 27 spectra, and the central core of the 2007 Nov 10 spectral map, reveal nearly featureless spectra, due to much larger grains that were ejected from the nucleus more slowly. We break the infrared image into three components (size, speed) that also explain the temporal evolution of the mm-wave flux. Optical images were obtained on multiple dates spanning 2007 Oct 27 to 2008 Mar 10 at the Holloway Comet Observatory and 1.5-m telescope at Palomar Observatory. The orientation of the leading edge of the ejecta shell and the ejecta blob, relative to the nucleus, do not change as the orientation of the Sun changes; instead, the configuration was imprinted by the orientation of the initial explosion. The kinetic energy of the ejecta >1e21 erg is greater than the gravitational binding energy of the nucleus. We model the explosion as being due to crystallization and release of volatiles from interior amorphous ice within a subsurface cavity; once the pressure in the cavity exceeded the surface strength, the material above the cavity was propelled from the comet. The size of the cavity and the tensile strength of the upper layer of the nucleus are constrained by the observed properties of the ejecta; tensile strengths on >10 m scale must be greater than 10 kPa. The appearance of the 2007 outburst is similar to that witnessed in 1892, but the 1892 explosion was less energetic by a factor of about 20.Comment: 51 pages. Some figures compressed (see real journal for full quality). accepted by Icaru

Crustal heterogeneity of the moon viewed from the Galileo SSI camera: Lunar sample calibrations and compositional implications

Summaries are given of the spectral calibration, compositional parameters, nearside color, and limb and farside color of the Moon. The farside of the Moon, a large area of lunar crust, is dominated by heavily cratered terrain and basin deposits that represent the products of the first half billion years of crustal evolution. Continuing analysis of the returned lunar samples suggest a magma ocean and/or serial magmatism model for evolution of the primordial lunar crust. However, testing either hypothesis requires compositional information about the crustal stratigraphy and lateral heterogeneity. Resolution of this important planetary science issue is dependent on additional data. New Galileo multispectral images indicate previously unknown local and regional compositional diversity of the farside crust. Future analysis will focus on individual features and a more detailed assessment of crustal stratigraphy and heterogeneity

Empirical investigation of a Stochastic model based on intensity values for terrestrial laser scanning

Stochastic information of measurements has always been an important part in the field of geodesy. Especially for engineering tasks like deformation monitoring the knowledge of achieved precision is of vital importance. For more than a decade terrestrial laser scanners have been used for high precise measurement applications, however there has been a lack of focus in the literature of an adequate stochastic model for terrestrial laser scanning. This contribution presents a comprehensive empirical experiment containing numerous laser scans at various scan configurations in order to examine a stochastic model based on intensity values. The results confirm the fundamental suitability of intensity values for a stochastic modelling but also point out certain problems concerning scanning geometry. High incidence angles in laser scanning can lead to an improvement of the precision in object's surface normal direction, which agrees with a previously proposed theoretical model for positional uncertainty of laser scan 3D points and should not be ignored in further development of a stochastic model based on intensity values. Based on these results a stochastic model was estimated and the precision of 3D points explicitly expressed as function of intensity and incidence angle

The impact of main belt asteroids on infrared--submillimetre photometry and source counts

> Among the components of the infrared and submillimetre sky background, the closest layer is the thermal emission of dust particles and minor bodies in the Solar System. This contribution is especially important for current and future infrared and submillimetre space instruments --like those of Spitzer, Akari and Herschel -- and must be characterised by a reliable statistical model. > We describe the impact of the thermal emission of main belt asteroids on the 5...1000um photometry and source counts, for the current and future spaceborne and ground-based instruments, in general, as well as for specific dates and sky positions. > We used the statistical asteroid model (SAM) to calculate the positions of main belt asteroids down to a size of 1km, and calculated their infrared and submillimetre brightness using the standard thermal model. Fluctuation powers, confusion noise values and number counts were derived from the fluxes of individual asteroids. > We have constructed a large database of infrared and submillimetre fluxes for SAM asteroids with a temporal resolution of 5 days, covering the time span January 1, 2000 -- December 31, 2012. Asteroid fluctuation powers and number counts derived from this database can be obtained for a specific observation setup via our public web-interface. > Current space instruments working in the mid-infrared regime (Akari and Spitzer Space Telescopes) are affected by asteroid confusion noise in some specific areas of the sky, while the photometry of space infrared and submillimetre instruments in the near future (e.g. Herschel and Planck Space Observatories) will not be affected by asteroids. Faint main belt asteroids might also be responsible for most of the zodiacal emission fluctuations near the ecliptic.Comment: accepted for publication in Astronomy & Astrophysics; Additional material (appendices) and the related web-interface can be found at: "http://kisag.konkoly.hu/solarsystem/irsam.html

Non-parametric belief propagation for mobile mapping sensor fusion

© 2016 Wuhan University. Published by Informa UK Limited, trading as Taylor & Francis Group. Many different forms of sensor fusion have been proposed each with its own niche. We propose a method of fusing multiple different sensor types. Our approach is built on the discrete belief propagation to fuse photogrammetry with GPS to generate three-dimensional (3D) point clouds. We propose using a non-parametric belief propagation similar to Sudderth et al’s work to fuse different sensors. This technique allows continuous variables to be used, is trivially parallel making it suitable for modern many-core processors, and easily accommodates varying types and combinations of sensors. By defining the relationships between common sensors, a graph containing sensor readings can be automatically generated from sensor data without knowing a priori the availability or reliability of the sensors. This allows the use of unreliable sensors which firstly, may start and stop providing data at any time and secondly, the integration of new sensor types simply by defining their relationship with existing sensors. These features allow a flexible framework to be developed which is suitable for many tasks. Using an abstract algorithm, we can instead focus on the relationships between sensors. Where possible we use the existing relationships between sensors rather than developing new ones. These relationships are used in a belief propagation algorithm to calculate the marginal probabilities of the network. In this paper, we present the initial results from this technique and the intended course for future work

Tohoku-Hiroshima-Nagoya planetary spectra library: A method for characterizing planets in the visible to near infrared

There has not been a comprehensive framework for comparing spectral data from different planets.Such a framework is needed for the study of extrasolar planets and objects within the solar system. We have undertaken observations to compile a library of planet spectra for all planets, some moons, and some dwarf planets in the solar system to study their general spectroscopic and photometric natures. During May and November of 2008, we acquired spectra for the planets using TRISPEC, which is capable of simultaneous three-band spectroscopy in a wide wavelength range of 0.45 - 2.5 microns with low resolving power (lambda-over-Delta-lambda is 140 - 360). Patterns emerge from comparing the spectra. Analyzing their general spectroscopic and photometric natures, we show that it is possible to distinguish between gas planets, soil planets and ice planets. These methods can be applied to extrasolar observations using low resolution spectrography or broad-band filters. The present planet spectral library is the first library to contain observational spectra for all of the solar system planets, based on simultaneous observations in visible and near infrared wavelengths. This library will be a useful reference for analyzing extrasolar planet spectra, and for calibrating planetary data sets.Comment: 11 pages, 6 figures, Accepted on 28/08/2009 to appear in Section 10. Planets and planetary systems of Astronomy and Astrophysic