Mutual Events Research Articles

A Two-Color Map of Pluto’s Sub-Charon Hemisphere

Pluto and its satellite Charon regularly occulted or transited each others disks from 1985 through 1990. The light curves resulting from these events (collectively called ii mutual events ˇˇ) have been used to determine albedo maps of Plutos sub-Charon hemisphere. We now use a data set of four light curves that were obtained in both B and V Johnson —lters to construct a two-color map of Plutos surface. We are able to resolve the central part of Plutos sub-Charon hemisphere. We —nd that the dark albedo feature that forms a band below Plutos equator is comprised of several distinct color units. We detect ratios of V -—lter/B-—lter normal re—ectances ranging from D1.15 to D1.39 on Plutos sub-Charon hemi- sphere. Key word: planets and satellites: individual (Pluto, Charon)

Mutual events between Jupiter's satellites observed in Catania during the PHEMU97 campaign

As a contribution to the PHEMU97 International Campaign, photoelectric observations of 80 phenomena between Jupiter's satellites were made at M.G. Fracastoro station. After the reduction, 28 lightcurves were analysed to provide elements useful to determine accurate photometric position. In the framework of their publication in the PHEMU97 catalogue a preliminary study on the agreement between the predicted and observed characteristics of the lightcurves is presented.

Mapping the Variegated Surface of Pluto

During the period from 1985 through 1990, Pluto and its satellite Charon underwent a series of transits, eclipses, and occultations, which are collectively called mutual events. The albedo distribution of Pluto's sub-Charon hemisphere can be determined from these events with a spatial resolution that surpasses any current direct-imaging schemes. We use an iterative technique to determine a map of Pluto's sub-Charon hemisphere with resolutions down to 200 km in some areas. This map resolves a localized bright feature that may be due to condensation around a geyser or in a crater.

Galilean satellite ephemerides E5

New ephemerides of Jupiter's Galilean satellites are produced from an analysis of CCD astrometric data, Voyager-mission optical navigation images, mutual event observations, photographic plates, and eclipse timing observations. The resulting parameters, for use in the galsat computer software, are in the B1950 frame for use by the Galileo space mission. Results in the J2000 system are also available.

A catalogue of the observations of the mutual phenomena of the Galilean satellites made in 1991 during the PHEMU91 campaign

In this paper, all the light-curves obtained during the PHEMU91 campaign of observations of the mutual phenomena of the Galilean satellites are presented. These observations give accurate astrometric positions of major interest for dynamical studies of the motion of the Galilean satellites. The aim of this work is to give obser- vational data directly usable for theoretical studies. We made 374 observations of 111 mutual events from 56 sites. The corresponding data are given in this paper 1 . The accu- racy of each observation has been deduced from a compar- ison with the theoretical predictions. For each observation, information is given about the telescope, the receptor, the site and the observational conditions.

Separate Lightcurves of Pluto and Charon

We present new Hubble Space Telescope observations of the Pluto–Charon system taken with WFPC1 (PC6) between 1992 May 21 and 1993 August 18. Our observations consist of 52 images with the F555W filter and 8 images in the F439W filter. From these data we extracted individual lightcurves, phase coefficients, and colors for Pluto and Charon. These lightcurves have peak-to-peak variations of 0.33 and 0.08 mag, respectively. The lightcurve for Charon is consistent with its suspected synchronous rotation about Pluto. The linear phase coefficients are 0.0294 ± 0.0011 mag/deg for Pluto and 0.0866 ± 0.0078 mag/deg for Charon, spanning a range of phase angles from 0.6° to 2.0°. Charon's lightcurve has far less structure than Pluto's with minimum light corresponding to the anti-Pluto hemisphere. We found theB–Vcolor of Charon to be 0.710 ± 0.011 mag. Combined with previous mutual event measurements, the color of Charon is seen to be globally uniform. We also confirmed a reddishB–Vcolor for Pluto of 0.873 ± 0.002 and 0.862 ± 0.002 mag at 123° and 289° east longitude, respectively. These colors are consistent with prior mutual event observations but the higher precision measurement indicates that the surface of Pluto is slightly redder near minimum light.

Galilean Satellites and the Galileo Space Mission

AbstractThe Galileo spacecraft arrived at Jupiter in December 1995 to start its two-year mission of exploring the Jovian system. The spacecraft will complete eleven orbits around Jupiter and have ten more close encounters with the outer three Galilean satellites, after the initial close approach to Io on December 7, 1995. Since the Io encounter occurred closer to Io than originally designed, the spacecraft energy change was greater than nominally planned and resulted in an initial spacecraft orbital period about 7 days less than that designed in the nominal tour. A 100-km change in the Io-encounter distance results in an 8-day change in initial period of the spacecraft. Hence the first Ganymede encounter was moved forward one week, and the aim points for the first two Ganymede encounters were altered, but all other encounters would occur on their nominal dates and at the nominal altitudes. This was accomplished without expending spacecraft fuel and resulted in the first Ganymede flyby occurring on June 27, 1996 rather than the nominally scheduled July 4.Earth- and spacecraft-based data were employed in developing ephemerides in support of the Galileo space mission. An analysis of CCD astrometric observations from 1992–1994, of photographic observations from 1967–1993, of mutual event astrometric data from 1973–1991, of Jovian eclipse timing data from 1652–1983, of Doppler data from 1987–1991, and of optical navigation data from the Voyager spacecraft encounter in 1979, produced the satellite ephemerides for the Galileo space mission.

Synoptic CCD Spectrophotometry of Pluto Over the Past 15 Years

Over the 15 years from 1980 to 1994, the same spectrometer has been used to obtain spectrophotometric observations of Pluto+Charon over the wavelength range from 0.5 to 1.0 μm. This time period spanned Pluto's perihelion passage in 1989, as well as the Pluto–Charon mutual event season. The data set is presented and a search made for variations in Pluto's methane absorptions and continuum slope correlating with Pluto's 6.4-day lightcurve as well as possible longer term secular evolution.Four quantities derived from Pluto's spectrum are examined for variation with Pluto's rotational phase. Although the depths of the methane bands are generally deeper away from the lightcurve minimum, they are found not to correlate in a simple way with the lightcurve, in contrast with the behavior of the stronger methane bands at longer wavelengths. This behavior implies that Pluto's CH4is not exclusively associated with the brightest or the darkest terrain, and that weak and strong methane bands are sensitive to different methane reservoirs on Pluto's surface. The wavelengths of CH4bands also change, being longest at the rotational phases where the CH4bands are deepest. The wavelength shifts can be attributed to variable concentration of CH4dissolved in N2ice. No statistically significant trend of bandwidth with longitude is detected. It is confirmed that the reddest slope of the continuum coincides with the darkest surface terrain. Examining spectral data pairs taken at similar Pluto longitudes, a modest but consistent secular trend is seen, with the depth of the 0.73-μm CH4absorption diminishing relative to that of the stronger 0.89-μm band.The observations are interpreted by means of Hapke scattering models. While unique solutions are not possible, it is found that the observed spectra can be matched by geographically diverse models possessing both methane rich and methane poor terrains. Terrain types proposed are a high albedo, CH4poor, N2dominated surface, a dark, red,tholin-rich surface, and a transitional zone, rich in CH4, with an intermediate albedo. The slight secular weakening of the 0.73-μm CH4band can be interpreted as resulting from differences between Pluto's southern and northern hemispheres or from a temporal evolution in the geographic proportions of the CH4rich and CH4poor terrains.

Reviewing the theories of motion of the satellites of Saturn

The state of knowledge of the motions of all Saturn's satellites is presented (excluding however the rings and their relating shepherding satellites). In particular, it appears that the theory of motion of the major satellites is now more precise than the available Earth-based observations, allowing to expect new progress with the next observations from mutual events and then with those from the Cassini mission.

New constants for Sampson-Lieske theory of the Galilean satellites of Jupiter from mutual occultation data

New constants for Sampson-Lieske theory of the Galilean Satellites have been derived using 6360 individual photographic positions (1891–1990) and 438 pseudo astrometric positions from mutual occultations during 1973, 1979, 1985 and 1991. Using these new sets of constants, significant improvement is noticed in the O-C values of the sky plane coordinates of the mutual event data set and residuals in longitude for Io and Europa are found to improve. Problems concerning the inclusion of mutual event data in attempting evaluation of secular variations of the mean motions of the satellites are discussed.

The PHESAT95 campaign of observations of the phenomena of the saturnian satellites

This paper reports on the international PHESAT95 campaign of observations of the Saturnian events coordinated by Bureau des longitudes. Thanks to CCD or photometric receptors, accurate astrometric data can be get from the observation of the eclipses by Saturn and mutual events of the Saturnian satellites. These events occur from 1994 to 1996 and we give our first results.

Modeling Pluto-Charon Mutual Events. II. CCD Observations With the 60 in. Telescope at Palomar Mountain

view Abstract Citations (9) References (29) Co-Reads Similar Papers Volume Content Graphics Metrics Export Citation NASA/ADS Modeling Pluto-Charon Mutual Events. II. CCD Observations With the 60 in. Telescope at Palomar Mountain Buratti, B. J. ; Dunbar, R. S. ; Tedesco, E. F. ; Gibson, J. ; Marcialis, R. L. ; Wong, F. ; Bennett, S. ; Dobrovolskis, A. Abstract We present observations of 15 Pluto-Charon mutual events which were obtained with the 60 in. telescope at Palomar Mountain Observatory. A CCD camera and Johnson V filter were used for the observations, except for one event that was observed with a Johnson B filter, and another event that was observed with a Gunn R filter. We observed two events in their entirety, and three pairs of complementary mutual occultation-transit events. Publication: The Astronomical Journal Pub Date: September 1995 DOI: 10.1086/117614 Bibcode: 1995AJ....110.1405B Keywords: PLANETS AND SATELLITES: INDIVIDUAL: CHARON; OCCULTATIONS full text sources ADS |

Mutual Events of Saturn's Satellites in 1995-1996

Around the times of the passages of Earth and the Sun through Saturn's ringplane, 198 mutual occultations and eclipses are predicted to occur between Saturn's major satellites between January 1995 and December 1996. To aid photometric observations, positions are also given of neighboring satellites within 10 arcsec of the occulted or eclipsed ones.

Observations of Pluto-Charon mutual events, 3

view Abstract Citations (2) References (4) Co-Reads Similar Papers Volume Content Graphics Metrics Export Citation NASA/ADS Observations of Pluto-Charon Mutual Events. III Blanco, C. ; di Martino, M. ; Ferreri, W. Abstract The results of the last mutual phenomena between Pluto and Charon, obtained from observations carried out as part of the planned 'Pluto-Charon Mutual Eclipse Season Campaign', are presented. We observed the phenomena, which occurred on 1989 May 28 and June 29 and 1990 June 28, in the B and V colors by using the 91 cm reflector of the Serra La Nave stellar station of Catania Astrophysical Observatory. From the analysis of the obtained light curves, with respect to the predicted ones, no large difference appears in the light losses and, as far as it is estimable, also in the times of the onset and of the end of the observed phenomena. Nevertheless, some disagreement is present between the predicted and observed times of the deepest points of the 1989 May 28 and 1990 June 28 light curves. Publication: The Astronomical Journal Pub Date: November 1994 DOI: 10.1086/117208 Bibcode: 1994AJ....108.1940B Keywords: Charon; Eclipses; Light Curve; Occultation; Pluto (Planet); Cassegrain Optics; Data Reduction; Error Analysis; Standard Deviation; Telescopes; Astronomy; PLANETS AND SATELLITES: INDIVIDUAL: PLUTO; PALNETS AND SATELLITES: INDIVIDUAL: CHARON full text sources ADS |

Mirages and the Nature of Pluto's Atmosphere

We present model occultation lightcurves demonstrating that a strong thermal inversion layer at the base of Pluto's stratosphere can reproduce the minimum flux measured by the Kuiper Airborne Observatory (KAO) during the 1988 occultation of a star by Pluto. The inversion layer also forms the occultation equivalent of a mirage at a radius of 1198 km, which is capable of hiding tropospheres of significant depth. Pluto's surface lies below 1198 km, its radius depending on the depth of the troposphere. We begin by computing plausible temperature structures for Pluto's lower atmosphere, constrained by a calculation of the temperature of the atmosphere near the surface. We then trace rays from the occulted star through the model atmosphere, computing the resultant bending of the ray. Model light curves are obtained by summing the contribution of individual rays within the shadow of Pluto on Earth. We find that we can reproduce the KAO lightcurve using model atmospheres with a temperature inversion and no haze. We have explored models with tropospheres as deep as 40 km (implying a Pluto radius of 1158 km) that reproduce the suite of occultation data. Deeper tropospheres can be fitted to the data, but the mutual event radius of 1150 km probably provides a lower bound. If Pluto has a shallow or nonexistent troposphere, its density is consistent with formation in the solar nebula with modest water loss due to impact ejection. If the troposphere is relatively deep, implying a smaller radius and larger density, signficant amounts of water loss are required.

A New Determination of Radii and Limb Parameters for Pluto and Charon from Mutual Event Lightcurves

Over the past several years Pluto-Charon mutual events have yielded progressively more accurate estimates of Charon's orbital elements and the radii of Pluto and Charon (e.g., Buie, Tholen, and Horne, 1992, Icarus 97, 211-227). Analysis of the 1988 stellar occultation by Pluto indicates a radius for Pluto that is about 4%, or 50 km +, larger than the mutual event radius of 1151 km. One possible explanation for the discrepancy is that the mutual event modeling treats Pluto and Charon as uniformly bright disks. If they are limb-darkened, the mutual event fits could underestimate their radii. In this paper we use an independent mutual event data set (Young and Binzel, 1992, Icarus 102, 134-149) to fit for Pluto and Charon's radii in a manner independent of either object's limb profile or albedo distribution. Our least-squares solution indicates that Pluto's radius is 1164 ± 22.9 km and Charon's radius is 621 ± 20.6 km.

Albedo Maps of Pluto and Improved Physical Parameters of the Pluto-Charon System

We present an analysis of photometric observations of the Pluto-Charon rotational and mutual event light curves obtained between 1982 and 1990. The dataset covers 18 satellite transits (inferior events) and 15 eclipses/occultations of Charon (superior events). From these data we derive refined orbital and physical parameters of the binary system and a geometric albedo map of Pluto's sub-Charon hemisphere using a multiparameter least-squares-fit method. Independently from the eclipse data, we deconvolve the rotational light curve, yielding the longitudinal albedo distribution on Pluto near perihelion. Our albedo maps reveal a highly contrasted planetary surface, in agreement with earlier reports obtained by other authors using different datasets and techniques. In particular, we confirm that the brightest and darkest regions on Pluto are the south and north polar caps, respectively. The mean albedo decreases from the mid latitudes of the northern hemisphere toward the mid latitudes of the southern hemisphere.

Eclipses and Mutual Events of the First Eight Saturnian Satellites during the 1993-1996 Period

Starting from July 1992, the apparent inclination of the orbital plane of the satellites of Saturn has begun to be small enough to induce phenomena. This configuration occurs every 15 years and gives the opportunity to observe eclipses and occultations of the first eight Saturnian satellites by the planet. Moreover, in 1995 and 1996, the Earth and Sun will pass through the plane of the rings and we will also observe mutual events of the Saturnian satellites: the satellites will eclipse and occult one another. We have computed the whole set of these phenomena and we give in this paper a selected set of eclipses by the planet and mutual events which could be observed under the best conditions: we will observe 163 eclipses by Saturn from 1993 May to 1996 August and 182 mutual eclipses and occultations from 1995 January to 1996 September. The observation of this type of event gives the opportunity to get astrometric measurements with a very high precision and will permit us to improve our knowledge of the dynamical motion of these satellites. Furthermore these observations are an interesting method for physical investigations concerning the atmosphere of Saturn or Titan, and they can he used for a photometric study of the surface scattering. We will organize a campaign and we call for observations of eclipses of the satellites by Saturn and for observations of their mutual events.

Pluto's Radius and Atmosphere: Results from the Entire 9 June 1988 Occultation Data Set

We have analyzed all photometric observations of the 9 June 1988 occultation of the star P8 by Pluto in order to derive the radius of Pluto and certain parameters of its atmosphere. Our analysis is based on a "haze" model; but where relevant, we also discuss the thermal gradient model. With either model, the occultation observations yield a diameter for the limb of Pluto that is significantly larger than that found from mutual event observations by D. J. Tholen and M. W. Buie (1989, Bull. Am. Astron. Soc. 21, 981-982), but is in good agreement with the value from E. F. Young (1992, Ph.D. thesis, Massachusetts Institute of Technology). For a clear atmosphere (i.e., the thermal gradient model), we find the radius of the solid surface of Pluto and, obviously, also of the limb, to be 1195 ± 5 km. If the haze model is correct, the solid surface of the planet falls below 1180 ± 5 km, but the radius of the visible limb would be in the haze layer between 1185 and 1200 km. The degree to which the structure of Pluto's atmosphere is globally homogeneous is also discussed.

MUTUAL AID IN OIL SPILL RESPONSE: THE ALASKAN NORTH SLOPE MODEL

ABSTRACT The Alaskan Arctic Region provides one of the world's most remote and challenging environments in which to mount an oil spill response. To facilitate the timeliness and appropriateness of the response, Alaska Clean Seas (ACS) and the operators of the North Slope oil fields have implemented a mutual aid concept for spill response. The concept is based upon each operator on the North Slope maintaining its own inventory of personnel [a spill response team (SRT)] and equipment that is available on short notice to respond to a spill. If the spill exceeds the responsible operator's resources, additional resources can be obtained from other operators and/or ACS through mutual aid. Individuals from diverse organizations are brought together in a mutual aid event. To allow different organizations to function effectively in a multi-organizational environment, a common management structure was required. The structure chosen for the North Slope was the incident command system (ICS). A key concern when discussing mutual aid is the provision of indemnification from liability for responders. For the North Slope, ACS and its member companies are indemnified when responding to a spill through provisions in the ACS charter and the ACS response action contract.