J. Pittichova

California Institute of Technology, Pasadena, California, United States

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Publications (150)98.87 Total impact

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    ABSTRACT: Using our photometric observations taken between April 1996 and January 2013 and other published data, we derive properties of the binary near-Earth asteroid (175706) 1996 FG3 including new measurements constraining evolution of the mutual orbit with potential consequences for the entire binary asteroid population. We also refined previously determined values of parameters of both components, making 1996 FG3 one of the most well understood binary asteroid systems. We determined the orbital vector with a substantially greater accuracy than before and we also placed constraints on a stability of the orbit. Specifically, the ecliptic longitude and latitude of the orbital pole are 266{\deg} and -83{\deg}, respectively, with the mean radius of the uncertainty area of 4{\deg}, and the orbital period is 16.1508 +\- 0.0002 h (all uncertainties correspond to 3sigma). We looked for a quadratic drift of the mean anomaly of the satellite and obtained a value of 0.04 +\- 0.20 deg/yr^2, i.e., consistent with zero. The drift is substantially lower than predicted by the pure binary YORP (BYORP) theory of McMahon and Scheeres (McMahon, J., Scheeres, D. [2010]. Icarus 209, 494-509) and it is consistent with the theory of an equilibrium between BYORP and tidal torques for synchronous binary asteroids as proposed by Jacobson and Scheeres (Jacobson, S.A., Scheeres, D. [2011]. ApJ Letters, 736, L19). Based on the assumption of equilibrium, we derived a ratio of the quality factor and tidal Love number of Q/k = 2.4 x 10^5 uncertain by a factor of five. We also derived a product of the rigidity and quality factor of mu Q = 1.3 x 10^7 Pa using the theory that assumes an elastic response of the asteroid material to the tidal forces. This very low value indicates that the primary of 1996 FG3 is a 'rubble pile', and it also calls for a re-thinking of the tidal energy dissipation in close asteroid binary systems.
    06/2014;
  • 01/2014;
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    ABSTRACT: Near-Earth asteroid (25143) Itokawa was visited by the Hayabusa spacecraft in 2005, resulting in a highly detailed shape and surface topography model. This model has led to several predictions for the expected radiative torques on this asteroid, suggesting that its spin rate should be decelerating.To detect changes in rotation rate that may be due to YORP-induced radiative torques, which in turn may be used to investigate the interior structure of the asteroid.Through an observational survey spanning 2001 to 2013 we obtained rotational lightcurve data at various times over the last five close Earth-approaches of the asteroid. We applied a polyhedron-shape-modelling technique to assess the spin-state of the asteroid and its long term evolution. We also applied a detailed thermophysical analysis to the shape model determined from the Hayabusa spacecraft.We have successfully measured an acceleration in Itokawa's spin rate of dw/dt=(3.54+/-0.38)*10-8rad/day2, equivalent to a decrease of its rotation period of ~45ms/yr. From the thermophysical analysis we find that the center-of-mass for Itokawa must be shifted by ~21m along the long-axis of the asteroid to reconcile the observed YORP strength with theory.This can be explained if Itokawa is composed of two separate bodies with very different bulk densities of 1750+/-110kg/m3 and 2850+/-500kg/m3, and was formed from the merger of two separate bodies, either in the aftermath of a catastrophic disruption of a larger differentiated body, or from the collapse of a binary system. We therefore demonstrate that an observational measurement of radiative torques, when combined with a detailed shape model, can provide insight into the interior structure of an asteroid. Futhermore, this is the first measurement of density inhomogeneity within an asteroidal body, that reveals significant internal structure variation. A specialised spacecraft is normally required for this.(2 data files).
    12/2013;
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    ABSTRACT: Near-Earth asteroid (25143) Itokawa was visited by the Hayabusa spacecraft in 2005, resulting in a highly detailed surface shape and topography model. This model has led to several predictions for the expected radiative torques on this asteroid, suggesting that its spin rate should be decelerating. Through an observational survey spanning 2001 to 2013 we have successfully measured an acceleration in its spin rate of dω/dt = 3.54 (± 0.38) × 10^(-8) rad day^(-2), equivalent to a decrease of its rotation period of ~ 45 ms year^(-1). Using the shape model determined from the Hayabusa spacecraft, we applied a detailed thermophysical analysis, to reconcile the predicted YORP strength with that observed. We find that the center-of-mass for Itokawa must be shifted by ~20 m along the long-axis of the asteroid to reconcile observations with theory. This can be explained if Itokawa is composed of two separate bodies with very different bulk densities of 1740 ± 110 kg m^(-3) and 2730 ± 440 kg m^(-3), and was formed from the merger of two separate bodies, consistent with the collapse of a binary system or the re-accumulation of material from a catastrophic collisional disruption. We demonstrate that an observational measurement of radiative torques, when combined with a detailed shape model, can provide insight into the interior structure of an asteroid.
    10/2013;
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    ABSTRACT: The near-Earth asteroid 163249 (2002 GT), classified as a potentially hazardous asteroid (PHA), has been identified a potential rendezvous target for the NASA Deep Impact spacecraft on 4 Jan 2020. As part of a coordinated international effort to study this asteroid during its 2013 apparition (J. Pittichová et al. DPS 2013), we obtained simultaneous Sloan r-band photometry at the Steward Observatory Bok 2.3-m telescope (+90Prime) and optical spectroscopic observations covering a wavelength interval from ~5400 to ~8500 Angstrom at the MMT 6.5-m (+RedChannel spectrograph) on 2013 June 16 and 17 UT near close Earth approach (heliocentric distance ~1.07 AU; geocentric distance ~0.13 AU) at 180 sec intervals over the ~3.76 hr rotational period. Our objective was to obtain a temporal sequence of spectra to assess surface mineralogy (seeking to potentially detect the 0.7 micron absorption bands attributed to phylosilicate materials) and to determine whether variations in the spectral slope and/or surface mineralogy are evident as a function of rotational period. Here we present initial analysis of these datasets, describing the light-curve and the reflectance spectra as a function of rotational phase. These datasets will be incorporated into a larger compendium describing the characteristics of asteroid 163249. Acknowledgement: This research supported in part by NASA 12-PAST-12-0010 grant NNX13AJ11G , and an appointment (E.L.R.) to the NASA Postdoctoral Program at the Goddard Space Flight Center, administered by Oak Ridge Associated Universities through a contract with NASA. Observations reported here were obtained at the MMT Observatory, a joint facility of the Smithsonian Institution and the University of Arizona. P.P. was supported by the Grant Agency of the Czech Republic, Grant P209/12/0229.
    10/2013;
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    ABSTRACT: Available from the Minor Planet Center.
    Minor Planet Electronic Circulars. 10/2013;
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    ABSTRACT: Available from the Minor Planet Center.
    Minor Planet Electronic Circulars. 10/2013;
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    ABSTRACT: Available from the Minor Planet Center.
    Minor Planet Electronic Circulars. 08/2013;
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    ABSTRACT: We present results from SEPPCoN, an on-going Survey of the Ensemble Physical Properties of Cometary Nuclei. In this report we discuss mid-infrared measurements of the thermal emission from 89 nuclei of Jupiter-family comets (JFCs). All data were obtained in 2006 and 2007 with the Spitzer Space Telescope. For all 89 comets, we present new effective radii, and for 57 comets we present beaming parameters. Thus our survey provides the largest compilation of radiometrically-derived physical properties of nuclei to date. We conclude the following. (a) The average beaming parameter of the JFC population is 1.03+/-0.11, consistent with unity, and indicating low thermal inertia. (b) The known JFC population is not complete even at 3 km radius, and even for comets with perihelia near ~2 AU. (c) We find that the JFC nuclear cumulative size distribution (CSD) has a power-law slope of around -1.9. (d) This power-law is close to that derived from visible-wavelength observations, suggesting that there is no strong dependence of geometric albedo with radius. (e) The observed CSD shows a hint of structure with an excess of comets with radii 3 to 6 km. (f) Our CSD is consistent with an intrinsic distribution that lacks many sub-kilometer objects.
    Icarus 07/2013; 226(1). · 3.16 Impact Factor
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    ABSTRACT: We present an analysis of comet activity based on the Spitzer Space Telescope component of the Survey of the Ensemble Physical Properties of Cometary Nuclei. We show that the survey is well suited to measuring the activity of Jupiter-family comets at 3-7 AU from the Sun. Dust was detected in 33 of 89 targets (37 +/- 6%), and we conclude that 21 comets (24 +/- 5%) have morphologies that suggest ongoing or recent cometary activity. Our dust detections are sensitivity limited, therefore our measured activity rate is necessarily a lower limit. All comets with small perihelion distances (q < 1.8 AU) are inactive in our survey, and the active comets in our sample are strongly biased to post-perihelion epochs. We introduce the quantity epsilon-f-rho, intended to be a thermal emission counterpart to the often reported A-f-rho, and find that the comets with large perihelion distances likely have greater dust production rates than other comets in our survey at 3-7 AU from the Sun, indicating a bias in the discovered Jupiter-family comet population. By examining the orbital history of our survey sample, we suggest that comets perturbed to smaller perihelion distances in the past 150 yr are more likely to be active, but more study on this effect is needed.
    Icarus 04/2013; 225(1). · 3.16 Impact Factor
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    ABSTRACT: Available from the Minor Planet Center.
    Minor Planet Electronic Circulars. 04/2013;
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    ABSTRACT: a b s t r a c t Observations from the second encounter of Comet 9P/Tempel 1 by the Stardust-NExT spacecraft provide an improved shape model and rotational pole for the nucleus (Thomas, P.C. et al. [2012]. Icarus 222, 453– 466) that allows us to greatly improve our knowledge of its rotational evolution beyond that outlined earlier in Belton et al. (Belton, M.J.S. et al. [2011]. Icarus 213, 345–368). Model light curves are shown to fit observations at both perihelia with a single pole direction indicating that polar precession during a single perihelion passage is small. We show that the rotational phasing associated with observations taken far from perihelion in the previous work was incorrectly assessed by approximately half a cycle leading us to a significant reassessment of the evolution of the non-gravitational torques acting on the nucleus. We present an updated spin rate profile (torque model) for the 2005 perihelion passage and show that retardation of the spin rate well before perihelion is no longer a required feature. With the exception of the spin rate before the 2000 perihelion passage, the evolution of rotational rates through the three most recent perihelion passages is largely unaffected as is the prediction of the rotational phase of the comet's nucleus at the Stardust-NExT near-perihelion encounter. We find a spin rate of 209.4 ± 0.01°/d likely applies in the quiescent period before the 2000 perihelion, a 0.2% change, and that the rotational period shortened by 12.3 ± 0.2 min during the 2000 perihelion passage. We present an analysis of Stardust-NExT time-series photometry that yields a spin rate near 213.3 ± 0.8°/d at the time of encounter. An application of the 2005 torque model suggests that, while roughly similar, the torques were probably weaker during the 2011 perihelion passage.
    Icarus 02/2013; 222:516-525. · 3.16 Impact Factor
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    ABSTRACT: Comet 85P/Boethin was selected as the original comet target for the Deep Impact extended mission, EPOXI. Because this comet had been only observed at two apparitions in 1975 and 1986 and consequently had a large ephemeris error, an early intense recovery effort similar to that of 1P/Halley was undertaken beginning in 2005 using the ESO Very Large Telescopes (VLTs) in a distant comet program. These were challenging observations because of the low galactic latitude, and an error ellipse (the line of variations) that was larger than the CCD FOV, and the comet was not seen. Dedicated recovery observing time was awarded on the Subaru telescope in April and May 2006, and June 2007, in addition to time on the VLT and Canada–France–Hawaii telescopes during July–August 2007 with wide field mosaics and mosaicing techniques. The limiting V magnitudes from these observing runs ranged between 25.7 and 27.3 and again the comet was not seen in the individual nights. A new image processing technique was developed to stack images over extended runs and runs after distorting them to account for dilations and rotations in the line of variations using modifications of the world coordinate system. A candidate at V ∼ 27.3 was found in the CFHT data along the LOV, 2.5′ west of the nominal ephemeris position. The EPOXI mission was unwilling to re-target the spacecraft without a confirmation. Additional time was secured using the Spitzer Space Telescope, the Gemini South 8-m telescope, the Clay and Baade (Magellan 6.5 m), CTIO 4 m, and SOAR 4 m telescopes during 2007 September and October A composite image made by stacking the new data showed no plausible candidate nucleus to a limiting magnitude of V = 28.5, corresponding to a nucleus radius between 0.1 and 0.2 km (assuming an albedo of 0.04). The comet was declared lost, presumably having disintegrated. Searches in the WISE data set revealed no debris trail, but no constraints on the possible time of disruption can be made. NASA approved the trajectory correction maneuver to go to Comet 103P/Hartley 2 on 2007 November 1. Many observers searched for the comet as it came to its December 2008 perihelion, but no trace of the nucleus was found.Based on observations collected at the Very Large Telescope, Chile, in part on data collected at Subaru Telescope, which is operated by the National Astronomical Observatory of Japan, in part using data gathered with the 6.5 m Magellan Telescopes located at Las Campanas Observatory, Chile, in part on observations obtained with MegaPrime/MegaCam, a joint project of CFHT and CEA/DAPNIA, at the Canada–France–Hawaii Telescope (CFHT) which is operated by the National Research Council (NRC) of Canada, the Institut National des Science de l’Univers of the Centre National de la Recherche Scientifique (CNRS) of France, and the University of Hawaii, in part using data collected at the Cerro Tololo Inter-American Observatory, National Optical Astronomy Observatory, which are operated by the Association for Research in Astronomy, under contract with the National Science Foundation, and in part on observations obtained at the Southern Astrophysical Research (SOAR) telescope, which is a joint project of the Ministério da Ciência, Tecnologia, e Inovação (MCTI) da República Federativa do Brasil, the U.S. National Optical Astronomy Observatory (NOAO), the University of North Carolina at Chapel Hill (UNC), and Michigan State University (MSU). This work is also based in part on observations taken with the Spitzer Space Telescope, which is operated by JPL/Caltech under a contract with NASA.
    Icarus 02/2013; 222(2):662–678. · 3.16 Impact Factor
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    ABSTRACT: The target of the NASA DIXI mission, comet 103P/Hartley 2 is in a non-principal-axis (NPA) rotational state that was observed to be varying with time. However, there is still no consensus on the specific NPA rotational state during the 103P/Hartley 2 encounter by DIXI. We analyze the continuum features observed in ground-based images bracketing the time of the DIXI encounter taken from a number of observatories located at different time zones to provide a dense temporal coverage. The continuum features are present at nearly all rotational phases (for the published periodicities of 18-hours and 55-hours). Therefore, we suggest the following possibilities for the origin of the continuum features and the implications. (a) If the features are originating from fixed source regions on the nucleus, short-axis-mode NPA states are more likely than the long-axis-mode NPA states, as the position angles of the observed features are restricted to a small range ( 65 degrees) in the sunlit side. (b) If the features are due to the aggregate effect of the sunward emission from the nucleus, then the continuum features cannot be used to exclude a particular mode of NPA rotation. However, the correct rotational model together with the activity model should be able to reproduce the observed coma features as a function of time. Dynamically, the moments of inertia of the near-prolate nucleus based on the shape model place severe constraints on the range of short-axis-mode states that are feasible. We will explore how non-uniform density distributions would affect the plausible NPA states and how they contrast with the case of uniform density. We will discuss both our analysis of the multi-observatory continuum images as well as the implications of non-uniform density distributions on the rotational state.
    AAS/Division for Planetary Sciences Meeting Abstracts; 10/2012
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    ABSTRACT: The Deep Impact spacecraft is currently on course for a proposed 2020-Jan-4 flyby of Potentially Hazardous Asteroid 163249 (2002 GT). The re-targeting will be complete with a final small maneuver scheduled for 2012-Oct-04. 2002 GT has a well-determined orbit and absolute magnitude 18.3 ( 800m diameter). Little more is known about the nature of this object, but in late June 2013 it will pass 0.012 AU from Earth, affording an exceptional opportunity for ground-based characterization. At this apparition 2002 GT will be in range of Arecibo, which should provide radar delay observations with precisions of a few microseconds, potentially revealing whether the system is binary or not. The asteroid will reach magnitude V=16.1 and will be brighter than V=18 for over two months, facilitating a host of observations at a variety of wavelengths. Light curve measurements across a wide range of viewing perspectives will reveal the rotation rate and ultimately lead to strong constraints on the shape and pole orientation. Visible and infrared spectra will constrain the mineralogy, taxonomy, albedo and size. Radar and optical astrometry will further constrain the orbit, both to facilitate terminal guidance operations and, when combined with spacecraft flyby data, to potentially reveal nongravitational forces acting on the asteroid. Coordinating all of these observations will be a significant task and we encourage interested observers to collaborate in this effort. The 2013 apparition will be the last time 2002 GT will be brighter than magnitude 18 until after the 2020 spacecraft flyby and thus represents a unique opportunity to characterize a potential flyby target, which will aid planning and development of the flyby imaging sequence and interpretation of flyby imagery. The knowledge gained from this proposed flyby will be highly relevant to NASA’s human exploration program, which desires more information on the characteristics of sub-kilometer near-Earth asteroids.
    10/2012;
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    ABSTRACT: We present observations of a statistically-significant number of Jupiter-family cometary nuclei as part of SEPPCoN (Survey of the Ensemble Physical Properties of Cometary Nuclei). We present preliminary results on distributions of albedos and shapes.
    LPI Contributions. 05/2012;
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    ABSTRACT: An analysis of photometric observations of binary Near-Earth asteroid (175706) 1996 FG3, taken from 1996 to 2012, gave a single solution for a quadratic drift of the mean anomaly of the satellite, 0.0 deg/yr^2, consistent with recent BYORP theory.
    LPI Contributions. 05/2012;
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    ABSTRACT: Comet P/2010 A2 LINEAR is an object on an asteroidal orbit within the inner main belt, therefore a good candidate for membership with the main belt comet family. It was observed with several telescopes (ESO New Technology Telescope, La Silla, Chile; Gemini North, Mauna Kea, Hawaii; University of Hawaii 2.2 m, Mauna Kea, Hawaii) from 14 Jan. until 19 Feb. 2010 in order to characterize and monitor it and its very unusual dust tail, which appears almost fully detached from the nucleus; the head of the tail includes two narrow arcs forming a cross. No evolution was observed during the span of the observations. Observations obtained during the Earth orbital plane crossing allowed an examination of the out-of-plane 3D structure of the tail. The immediate surroundings of the nucleus were found dust-free, which allowed an estimate of the nucleus radius of 80-90 m, assuming an albedo p = 0.11 and a phase correction with G = 0.15 (values typical for S-type asteroids). A model of the thermal evolution indicates that such a small nucleus could not maintain any ice content for more than a few million years on its current orbit, ruling out ice sublimation dust ejection mechanism. Rotational spin-up and electrostatic dust levitations were also rejected, leaving an impact with a smaller body as the favoured hypothesis. This is further supported by the analysis of the tail structure. Finston-Probstein dynamical dust modelling indicates the tail was produced by a single burst of dust emission. More advanced models (described in detail in a companion paper), independently indicate that this burst populated a hollow cone with a half-opening angle α ~ 40° and with an ejection velocity vmax ~ 0.2 m s-1, where the small dust grains fill the observed tail, while the arcs are foreshortened sections of the burst cone. The dust grains in the tail are measured to have radii between a = 1-20 mm, with a differential size distribution proportional to a-3.44 ± 0.08. The dust contained in the tail is estimated to at least 8 × 108 kg, which would form a sphere of 40 m radius (with a density ρ = 3000 kg m-3 and an albedo p = 0.11 typical of S-type asteroids). Analysing these results in the framework of crater physics, we conclude that a gravity-controlled crater would have grown up to ~100 m radius, i.e. comparable to the size of the body. The non-disruption of the body suggest this was an oblique impact. Based on observations collected at the Gemini North Observatory, Mauna Kea, Hawaii, USA, program GN-2009B-DD-10 at the European Southern Observatory, La Silla, Chile, program 184.C-1143(A), and at the University of Hawaii 2.2-m telescope, Mauna Kea, Hawaii, USA.
    Astronomy and Astrophysics 01/2012; · 5.08 Impact Factor
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    ABSTRACT: Comet P/2010A2 LINEAR is a good candidate for membership with the Main Belt Comet family. It was observed with several telescopes (ESO NTT, La Silla; Gemini North, Mauna Kea; UH 2.2m, Mauna Kea) from 14 Jan. until 19 Feb. 2010 in order to characterize and monitor it and its very unusual dust tail, which appears almost fully detached from the nucleus; the head of the tail includes two narrow arcs forming a cross. The immediate surroundings of the nucleus were found dust-free, which allowed an estimate of the nucleus radius of 80-90m. A model of the thermal evolution indicates that such a small nucleus could not maintain any ice content for more than a few million years on its current orbit, ruling out ice sublimation dust ejection mechanism. Rotational spin-up and electrostatic dust levitations were also rejected, leaving an impact with a smaller body as the favoured hypothesis, and ruling out the cometary nature of the object. The impact is further supported by the analysis of the tail structure. Finston-Probstein dynamical dust modelling indicates the tail was produced by a single burst of dust emission. More advanced models, independently indicate that this burst populated a hollow cone with a half-opening angle alpha~40degr and with an ejection velocity v_max ~ 0.2m/s, where the small dust grains fill the observed tail, while the arcs are foreshortened sections of the burst cone. The dust grains in the tail are measured to have radii between a=1-20mm, with a differential size distribution proportional to a^(-3.44 +/- 0.08). The dust contained in the tail is estimated to at least 8x10^8kg, which would form a sphere of 40m radius. Analysing these results in the framework of crater physics, we conclude that a gravity-controlled crater would have grown up to ~100m radius, i.e. comparable to the size of the body. The non-disruption of the body suggest this was an oblique impact.
    12/2011;

Publication Stats

339 Citations
98.87 Total Impact Points

Institutions

  • 2014
    • California Institute of Technology
      • Jet Propulsion Laboratory
      Pasadena, California, United States
  • 2013
    • Slovak Academy of Sciences
      • Astronomical Institute
      Presburg, Bratislavský, Slovakia
  • 2003–2013
    • Honolulu University
      Honolulu, Hawaii, United States
  • 2011
    • University of Hawaiʻi at Hilo
      Hilo, Hawaii, United States
  • 2009
    • University of Hawai'i System
      Honolulu, Hawaii, United States
  • 2005–2008
    • University of Hawaiʻi at Mānoa
      • Institute of Astronomy
      Honolulu, HI, United States