ABSTRACT: We describe a strategy for scheduling astrometric observations to minimize the number required to determine the mutual orbits of binary transneptunian systems. The method is illustrated by application to Hubble Space Telescope observations of (42355) Typhon-Echidna, revealing that Typhon and Echidna orbit one another with a period of 18.971 +/- 0.006 days and a semimajor axis of 1628 +/- 29 km, implying a system mass of (9.49 +/- 0.52) x 10^17 kg. The eccentricity of the orbit is 0.526 +/- 0.015. Combined with a radiometric size determined from Spitzer Space Telescope data and the assumption that Typhon and Echidna both have the same albedo, we estimate that their radii are 76 +14/-16 and 42 +8/-9 km, respectively. These numbers give an average bulk density of only 0.44 +0.44/-0.17 g cm^-3, consistent with very low bulk densities recently reported for two other small transneptunian binaries.
ABSTRACT: We report here initial results of the Deep Ecliptic Survey, an ongoing new search for Kuiper belt objects (KBOs) and Centaurs using the 8K × 8K Mosaic CCD array on the 4 m Mayall Telescope at Kitt Peak National Observatory. Within the interval covered in this paper, useful observations were obtained during seven nights in 1998 October and November, 1999 April, and 2000 February. We used a novel technique to efficiently find and determine positions of moving objects. Sixty-nine KBOs and Centaurs with apparent magnitudes between 20.6 and approximately the 24th magnitude were discovered. Nine or 10 of the newly discovered KBOs appear to be in the 3 : 2 mean motion resonance with Neptune, and four appear to be scattered-disk objects. Three objects were found that may be in the 4 : 3 resonance. Sixty-two of the objects reported here have been observed on at least one additional night and have received designations. Our own follow-up astrometry was done primarily with the WIYN 3.5 m telescope in queue-scheduled mode and with the Steward Observatory 90 inch (2.3 m) telescope. Others, using a variety of telescopes, recovered a significant number of our objects. Although not a primary objective of the survey, positions of all main-belt asteroids, Trojan asteroids, and nearby fast-moving asteroids seen in our data also have been determined, and most have been reported to the Minor Planet Center. Through simulations and analysis of the existing KBO database, we have investigated the uncertainty to be expected in various KBO orbital parameters as a function of the extent of the astrometric coverage. The results indicate that the heliocentric distance of an object and the inclination of its orbit can be narrowly constrained with observations from a single apparition. Accurate determination of semimajor axis and eccentricity, on the other hand, requires astrometric data extending over additional apparitions. Based on the observed distribution of orbital inclinations in our sample, we have estimated the true distribution of orbital inclinations in the Kuiper belt and find it to be similar to that of the short-period comets. This result is consistent with the commonly held belief that the Kuiper belt is the source region of the short-period comets.
The Astronomical Journal 12/2007; 123(4):2083. · 4.03 Impact Factor
ABSTRACT: Visible wavelength observations were made of the 2007 March 18 Pluto
occultation of the star P445.3 (UCAC2 25823784; McDonald and Elliot, AJ
120, 1599) from five US sites by our consortium (Pasachoff, et al.,
2007, this meeting). Simultaneous model fitting to all of our light
curve data yielded 1207 ± 4 km as the half-light shadow radius of
Pluto's atmosphere. This radius is consistent with the 1208 ± 9
km result measured in 2006 (Elliot, et al., AJ 134,1) and confirms that
the large increase in atmospheric pressure measured between the 1988 and
2002 (Elliot, et al., Nature 424,165 Sicardy, et al., Nature 424, 168)
observations has ceased. Inversion of the highest signal-to-noise
visible light curve, obtained with the Portable Occultation Eclipse and
Transit Systems (POETS; Souza, et al., PASP 118, 1550) at the 6.5-m MMT
(MMTO, Fred Lawrence Whipple Observatory, Mt. Hopkins) resulted in
number density, pressure, and temperature profiles for Pluto's
atmosphere in the radius range of 1340 - 1460 km (assuming the dominant
atmospheric component is N2). These inversions reveal
oscillating deviations of the number density from a simple exponential
profile in Pluto's upper atmosphere that are coherent across the 1000 km
length of the grazing occultation and also in the 300 km line of sight.
Here, we interpret this structure as vertically propagating waves in
Pluto's upper atmosphere, and provide a feasible mechanism for the
maintenance of this large-scale coherence in terms of Rossby planetary
waves. This work was partially funded by NASA Planetary Astronomy grants
NNG04GE48G, NNG04GF25G, NNH04ZSS001N, and NNG05GG75G. Partial funding
for MMTO observations was also provided by Astronomy Camp. Some of the
observations reported here were obtained at the MMT Observatory, a joint
facility of the University of Arizona and the Smithsonian Institution.
ABSTRACT: Hubble Space Telescope observations of Uranus- and Neptune-crossing object (65489) Ceto/Phorcys (provisionally designated 2003 FX128) reveal it to be a close binary system. The mutual orbit has a period of 9.554 +/- 0.011 days and a semimajor axis of 1840 +/- 48 km. These values enable computation of a system mass of (5.41 +/- 0.42) 10^18 kg. Spitzer Space Telescope observations of thermal emission at 24 and 70 microns are combined with visible photometry to constrain the system's effective radius (109 +10/-11 km) and geometric albedo (0.084 +0.021/-0.014). We estimate the average bulk density to be 1.37 +0.66/-0.32 g cm^-3, consistent with ice plus rocky and/or carbonaceous materials. This density contrasts with lower densities recently measured with the same technique for three other comparably-sized outer Solar System binaries (617) Patroclus, (26308) 1998 SM165, and (47171) 1999 TC36, and is closer to the density of the saturnian irregular satellite Phoebe. The mutual orbit of Ceto and Phorcys is nearly circular, with an eccentricity <= 0.015. This observation is consistent with calculations suggesting that the system should tidally evolve on a timescale shorter than the age of the solar system.
ABSTRACT: We have started a project to see how a process of statistical ranging
might be used to help recover short-arc KBOs and (at least
qualitatively) classify such objects even if they are never actually
recovered. Starting with a nominal orbit fitted to the observations of a
KBO with a short observational arc, we allow the fitted orbital elements
to vary (usually by 1 sigma, but constrained to allow only valid
Keplerian elements). This modified orbit is used to generate a "new"
observation at some later time T. An orbit is then fitted to the
original observations plus the "new" observation. If the resulting orbit
still fits the original observations, we save the elements, the
predicted position at time T, and the RMS between the original
observations and the positions resulting from the new orbit at those
times. The process is repeated until we have a "reasonably" large number
of test orbits (500-1000 seems to work). Using the Keplerian elements
for each of the test orbits, we can assign a rough classification to
each orbit from its location in the a-e plane. The resulting data set
serves several purposes. For example, we can determine a "statistical"
classification for an object given our data set of possible
classifications. Clearly, not all KBOs that the Deep Ecliptic Survey has
discovered can be recovered in the near future. A "statistical"
classification can help de-bias our entire data set. The data can also
be used for recoveries, especially when the distribution extends beyond
the nominal error ellipse for the KBO. If an object is not found in the
predicted sky area for a certain dynamical class, than statistically it
is likely to belong to a different dynamical class.
This work was supported by NASA Grants NNG06GI23G, NG05GH86G, NAG5-13380
and NSF grant NSF-8406493 .
ABSTRACT: The heliocentric orbit of Centaur object (65489) 2003 FX128
has a high eccentricity and crosses the orbits of Uranus and Neptune.
This orbit is unstable, suggesting the object was perturbed relatively
recently from an orbit in the Kuiper belt and has experienced close
encounters along the way with one or more giant planets. Hubble Space
Telescope visual images in 2006 April and May show it to be a tight
binary system with a secondary component about 0.6 mag fainter than the
primary, making it the second binary Centaur to be discovered after 2002
CR46. Their mutual orbit has a period of 9.554±0.011
days and a semimajor axis of 1842±46; km, enabling us to compute
the system mass as 5.42±0.42 x 1018 kg. Spitzer Space
Telescope thermal infrared observations were executed in 2006 July, and
the data will soon be returned to Earth. These data will constrain the
size and albedo, and, in combination with the mass from the satellite's
orbit, the bulk density of (65489) 2003 FX128. The physical
properties of (65489) 2003 FX128 revealed by Hubble and
Spitzer observations will be described and compared with recent findings
for other trans-neptunian objects and Centaurs. We will also discuss the
implications of the circular nature of the satellite's orbit (the upper
limit on its eccentricity is 0.015).
ABSTRACT: The physical characteristics of Pluto and its moon, Charon, provide insight into the evolution of the outer Solar System. Although previous measurements have constrained the masses of these bodies, their radii and densities have remained uncertain. The observation of a stellar occultation by Charon in 1980 established a lower limit on its radius of 600 km (ref. 3) (later refined to 601.5 km; ref. 4) and suggested a possible atmosphere. Subsequent, mutual event modelling yielded a range of 600-650 km (ref. 5), corresponding to a density of 1.56 +/- 0.22 g cm(-3) (refs 2, 5). Here we report multiple-station observations of a stellar occultation by Charon. From these data, we find a mean radius of 606 +/- 8 km, a bulk density of 1.72 +/- 0.15 g cm(-3), and rock-mass fraction 0.63 +/- 0.05. We do not detect a significant atmosphere and place 3sigma upper limits on atmospheric number densities for candidate gases. These results seem to be consistent with collisional formation for the Pluto-Charon system in which the precursor objects may have been differentiated, and they leave open the possibility of atmospheric retention by the largest objects in the outer Solar System.
Nature 02/2006; 439(7072):48-51. · 36.28 Impact Factor
ABSTRACT: The physical characteristics of Pluto and its moon, Charon, provide insight into the evolution of the outer Solar System. Although previous measurements have constrained the masses of these bodies
Nature 01/2006; 439(7072):48-51. · 36.28 Impact Factor
ABSTRACT: The Deep Ecliptic Survey is a project whose goal is to survey a large area of the near-ecliptic region to a faint limiting magnitude (R ~ 24) in search of objects in the outer solar system. We are collecting a large homogeneous data sample from the Kitt Peak Mayall 4-m and Cerro Tololo Blanco 4-m telescopes with the Mosaic prime-focus CCD cameras. Our goal is to collect a sample of 500 objects with good orbits to further our understanding of the dynamical structure of the outer solar system. This survey has been in progress since 1998 and is responsible for 272 designated discoveries as of March 2003. We summarize our techniques, highlight recent results, and describe publically available resources. Comment: Earth, Moon, and Planets, as part of First Decadal Review of the Edgeworth-Kuiper Belt special issue, peer-reviewed and accepted
ABSTRACT: Stellar occultations--the passing of a relatively nearby body in front of a background star--can be used to probe the atmosphere of the closer body with a spatial resolution of a few kilometres (ref. 1). Such observations can yield the scale height, temperature profile, and other information about the structure of the occulting atmosphere. Occultation data acquired for Pluto's atmosphere in 1988 revealed a nearly isothermal atmosphere above a radius of approximately 1,215 km. Below this level, the data could be interpreted as indicating either an extinction layer or the onset of a large thermal gradient, calling into question the fundamental structure of this atmosphere. Another question is to what extent Pluto's atmosphere might be collapsing as it recedes from the Sun (passing perihelion in 1989 in its 248-year orbital period), owing to the extreme sensitivity of the equilibrium surface pressure to the surface temperature. Here we report observations at a variety of visible and infrared wavelengths of an occultation of a star by Pluto in August 2002. These data reveal evidence for extinction in Pluto's atmosphere and show that it has indeed changed, having expanded rather than collapsed, since 1988.
Nature 08/2003; 424(6945):165-8. · 36.28 Impact Factor
ABSTRACT: Processes relevant to Pluto's atmosphere are discussed,and our current knowledge is summarized, including results of two stellar occultationsby Pluto that were observed in 2002. The question of whether other Kuiper belt objects (KBOs)may have bound atmospheres is considered, and observational indicators for KBO atmospheresare described. The definitive detection of a KBO atmosphere could be established withtargeted stellar-occultation observations. These data can also establish accurate diametersfor these objects and be used to detect possible nearby companions. Strategies for acquiringoccultation data with portable, airborne, and fixed telescopes are evaluated in terms of thenumber of KBO occultations per year that should be observable. For the sample of 29 currentlyknown KBOs with H 5.2, (radius 300 km for a geometricalbedo of 0.04), we expect about 4 events per year would yield good results for a (stationary) 6.5-m telescope. A network of portable0.36-m telescopes should be able to observe 6 events per year, and a 2.5-m airborne telescopewould have about 200 annual opportunities to observe KBO occultations.
Earth Moon and Planets 05/2003; 92(1):375-393. · 0.67 Impact Factor
ABSTRACT: As part of our ongoing Deep Ecliptic Survey (DES) of the Kuiper belt, we report on the occupation of the 1:1 (Trojan), 4:3, 3:2, 7:4, 2:1, and 5:2 Neptunian mean-motion resonances (MMRs). The occupation of the 1:1 and 5:2 MMRs is not easily understood within the standard model of resonance sweeping by a migratory Neptune over an initially dynamically cold belt. Our dynamically hot, 5:2 resonant objects can librate with modest amplitudes of 90 deg within the resonance for at least 1 Gyr. Their trajectories cannot be explained by close encounters with Neptune alone, given the latter's current orbit. The hot orbits of such 5:2 resonant KBOs, unlike hot orbits of previously known resonant KBOs, may imply that these objects were pre-heated to large inclination and large eccentricity prior to resonance capture by a migratory Neptune. Our first discovered Neptunian Trojan, 2001QR322, may not owe its existence to Neptune's migration at all. The trajectory of 2001QR322 is remarkably stable; the object can undergo tadpole-type libration about Neptune's leading Lagrange (L4) point for at least 1 Gyr with a libration amplitude of 24 deg. Trojan capture probably occurred while Neptune accreted the bulk of its mass. For an assumed albedo of 12--4%, our Trojan is 130--230 km in diameter. Model-dependent estimates place the total number of Neptune Trojans resembling 2001QR322 at 20--60. Their existence might rule out violent orbital histories for Neptune. Comment: Accepted to AJ, final version, contains list of names of all resonant KBOs known to humanity as of Feb 1 2003
ABSTRACT: Following our discovery of 2001 QT297 as the second knownbinary Edgeworth–Kuiper Belt Object (EKBO) in October of 2001 [IAUC 7733], we havecarried out additional high spatial resolution ground based imaging in October andNovember of 2001 and July, August, and September of 2002. Using the Raymond andBeverly Sackler Magellan Instant Camera (MagIC) on the Baade and Clay 6.5 m telescopesat Las Campanas Observatory in Chile, we have obtained accurate astrometric and photometricmeasurements in the Sloan r i and g filters. Superb seeing conditions andPSF fitting allow an accurate determination of the binary component separation and positionangle over time as well as a detailed study of color and temporal variability of the individualcomponents. Here we present a physical characterization of the individual componentsof 2001 QT297 based on these astrometric, color and variability measurements. We findthe primary to exhibit colors about 0.3 magnitudes redder than solar with no evidencefor variability. The secondary component, however, exhibits strong variability(0.6 magnitudes) with a best fit period of 4.7526 0.0007 h for a single peaklightcurve or 9.505 0.001 h for a dual peaked lightcurve. The colors measured for thesecondary also suggest variability. Based on a preliminary orbit fit for thepair using observations spanning a one year arc, we are able to estimate a system mass of 3.2 1018 kg and provide constraints to the surface albedo of 9–14% for assumeddensities between 1 and 2 g/cm3.
Earth Moon and Planets 01/2003; 92(1):409-421. · 0.67 Impact Factor
ABSTRACT: The Deep Ecliptic Survey is a search for Kuiper Belt Objects and
Centaurs being conducted on the 4-meter telescopes at KPNO and CTIO with
the MOSAIC cameras. A description of the search methods and initial
results, based on the first 69 objects discovered, has been published
(Millis et al., Astron. J. 123, 2083-2109, 2002). At this writing
(August 1, 2002), 219 KBOs and Centaurs discovered in the survey have
received preliminary designations or permanent numbers. Included are
three objects that have turned out to be binary (1998 WW31,
2001 QT297, and 2000 CF105); 28978 Ixion, the
intrinsically brightest KBO; the extended and near scattered disk
objects, 2000 CR105 and 2000 OO67; the dynamically
young object, 2000 QB243; and a handful of objects in the
8:5, 7:4, 4:3, 6:5, and 2:1 resonances. Extensive data products from the
survey are available to the community on the Lowell Observatory website
(http://www.lowell.edu/Research/DES/). The survey images themselves will
soon be available in the NOAO archive. In this paper, we will discuss
the current status of the survey, address various challenges we are
facing, and describe a new automated and objective method for assigning
newly discovered objects to one of five dynamical classes. This research
is supported in part by NASA and NSF. The NOAO facilities used in the
survey are funded by NSF through a contract to AURA.
ABSTRACT: One reason to expect a trans-Neptunian disk population as the source of
the short period comets is that the orbits of the short period comets
have small inclinations compared with the distribution of orbital
inclinations that would be expected from an Oort-cloud source (Duncan,
Quinn & Tremaine, 1988, ApJL 328, L69). Hence one of the objectives
of our deep ecliptic survey with the Mosaic cameras at KPNO and CTIO
(Millis et al., this conference) is the determination of the inclination
distribution for Kuiper Belt Objects, in order to compare it with that
of the short period comets. Although most of our survey has occurred
within a few degrees of the ecliptic, orbits of all inclinations pass
through this region. We have confirmed discoveries of KBOs with a
variety of inclinations (the greatest being 31 degrees), and confirmed
discoveries of KBOs by others with inclinations as high as 40 degrees
have been reported to the Minor Planet Center. A body in an orbit of
high inclination, of course, spends a small fraction of its period near
the ecliptic, but this observational bias can be removed. We shall
present the unbiased orbital-inclination distribution for the KBOs
discovered by our survey. This work has been supported, in part, by NASA
Grants NAG5-8990 to Lowell Observatory, and NAG5-3940 to MIT.
ABSTRACT: Hubble Space Telescope observations of Uranus- and Neptune-crossing object (65489) Ceto/Phorcys (provisionally designated 2003 FX128) reveal it to be a close binary system. The mutual orbit has a period of 9.554±0.011 days and a semimajor axis of 1840±48 km. These values enable computation of a system mass of (5.41±0.42)×1018 kg. Spitzer Space Telescope observations of thermal emission at 24 and 70 μm are combined with visible photometry to constrain the system's effective radius and geometric albedo . We estimate the average bulk density to be , consistent with ice plus rocky and/or carbonaceous materials. This density contrasts with lower densities recently measured with the same technique for three other comparably-sized outer Solar System binaries (617) Patroclus, (26308) 1998 SM165, and (47171) 1999 TC36, and is closer to the density of the saturnian irregular satellite Phoebe. The mutual orbit of Ceto and Phorcys is nearly circular, with an eccentricity ⩽0.015. This observation is consistent with calculations suggesting that the system should tidally evolve on a timescale shorter than the age of the Solar System.
ABSTRACT: We present photometric and astrometric results from four epochs of ground-based observations at the Magellan telescopes of the Kuiper belt binary 2003QY90. Resolved observations show both components to be highly variable and often of nearly equal brightness, causing difficulty in distinguishing between the primary and secondary components for observations spaced widely in time. Resolved lightcurve observations on one night show one component to have a single-peaked rotation period of 3.4±1.1 h and a peak-to-peak amplitude of 0.34±0.12 mag. The other component exhibits a less constrained lightcurve, with a single-peaked rotation period of 7.1±2.9 h and a peak-to-peak amplitude of 0.90±0.36 mag. Under the assumption of equal albedos, the diameter ratio is 1.25±0.11 in the Sloan i′ filter. While we cannot determine an orbit from our four distinct epochs of observation (due to ambiguity in component identification), we place limits on the orbital period of the system of 300–600 days, we find a minimum semi-major axis of 13,092 km for a circular orbit and a system mass range of (2.3–18.0)×1017 kg depending on the identification of components in our observations.