1,009 research outputs found
Water Ice in 2060 Chiron and its Implications for Centaurs and Kuiper Belt Objects
We report the detection of water ice in the Centaur 2060 Chiron, based on
near-infrared spectra (1.0 - 2.5 micron) taken with the 3.8-meter United
Kingdom Infrared Telescope (UKIRT) and the 10-meter Keck Telescope. The
appearance of this ice is correlated with the recent decline in Chiron's
cometary activity: the decrease in the coma cross-section allows previously
hidden solid-state surface features to be seen. We predict that water ice is
ubiquitous among Centaurs and Kuiper Belt objects, but its surface coverage
varies from object to object, and thus determines its detectability and the
occurrence of cometary activity.Comment: 18 pages, 3 figures, accepted by ApJ Letter
Population of the Scattered Kuiper Belt
We present the discovery of three new Scattered Kuiper Belt Objects (SKBOs)
from a wide-field survey of the ecliptic. This continuing survey has to date
covered 20.2 square degrees to a limiting red magnitude of 23.6. We combine the
data from this new survey with an existing survey conducted at the University
of Hawaii 2.2m telescope to constrain the number and mass of the SKBOs. The
SKBOs are characterized by large eccentricities, perihelia near 35 AU, and
semi-major axes > 50 AU. Using a maximum-likelihood model, we estimate the
total number of SKBOs larger than 100 km in diameter to be N = 3.1 (+1.9/-1.3)
x 10^4 (1 sigma) and the total mass of SKBOs to be about 0.05 Earth masses,
demonstrating that the SKBOs are similar in number and mass to the Kuiper Belt
inside 50 AU.Comment: 15 pages, 3 figure
A new perspective on the irregular satellites of Saturn - I Dynamical and collisional history
The dynamical features of the irregular satellites of the giant planets argue
against an in-situ formation and are strongly suggestive of a capture origin.
Since the last detailed investigations of their dynamics, the total number of
satellites have doubled, increasing from 50 to 109, and almost tripled in the
case of Saturn system. We have performed a new dynamical exploration of Saturn
system to test whether the larger sample of bodies could improve our
understanding of which dynamical features are primordial and which are the
outcome of the secular evolution of the system. We have performed detailed
N--Body simulations using the best orbital data available and analysed the
frequencies of motion to search for resonances and other possible perturbing
effects. We took advantage of the Hierarchical Jacobian Symplectic algorithm to
include in the dynamical model of the system also the gravitational effects of
the two outermost massive satellites, Titan and Iapetus. Our results suggest
that Saturn's irregular satellites have been significantly altered and shaped
by the gravitational perturbations of Jupiter, Titan, Iapetus and the Sun and
by the collisional sweeping effect of Phoebe. In particular, the effects on the
dynamical evolution of the system of the two massive satellites appear to be
non-negligible. Jupiter perturbs the satellites through its direct
gravitational pull and, indirectly, via the effects of the Great Inequality,
i.e. its almost resonance with Saturn. Finally, by using the Hierarchical
Clustering Method we found hints to the existence of collisional families and
compared them with the available observational data.Comment: 26 Pages, 27 Figures, 4 Table
The rotation and coma profiles of comet C/2004 Q2 (Machholz)
Aims. Rotation periods of cometary nuclei are scarce, though important when
studying the nature and origin of these objects. Our aim is to derive a
rotation period for the nucleus of comet C/2004 Q2 (Machholz). Methods. C/2004
Q2 (Machholz) was monitored using the Merope CCD camera on the Mercator
telescope at La Palma, Spain, in January 2005, during its closest approach to
Earth, implying a high spatial resolution (50km per pixel). One hundred seventy
images were recorded in three different photometric broadband filters, two blue
ones (Geneva U and B) and one red (Cousins I). Magnitudes for the comet's
optocentre were derived with very small apertures to isolate the contribution
of the nucleus to the bright coma, including correction for the seeing. Our CCD
photometry also permitted us to study the coma profile of the inner coma in the
different bands. Results. A rotation period for the nucleus of P = 9.1 +/- 0.2
h was derived. The period is on the short side compared to published periods of
other comets, but still shorter periods are known. Nevertheless, comparing our
results with images obtained in the narrowband CN filter, the possibility that
our method sampled P/2 instead of P cannot be excluded. Coma profiles are also
presented, and a terminal ejection velocity of the grains v_gr = 1609 +/- 48
m/s is found from the continuum profile in the I band.Comment: 11 pages, 9 figures, accepted by A&
Irregular Satellites of the Planets: Products of Capture in the Early Solar System
All four giant planets in the Solar system possess irregular satellites,
characterized by large, highly eccentric and/or inclined orbits that are
distinct from the nearly circular, uninclined orbits of the regular satellites.
This difference can be traced directly to different modes of formation. Whereas
the regular satellites grew by accretion within circumplanetary disks the
irregular satellites were captured from initially heliocentric orbits at an
early epoch. Recently, powerful survey observations have greatly increased the
number of known irregular satellites, permitting a fresh look at the group
properties of these objects and motivating a re-examination of the mechanisms
of capture. None of the suggested mechanisms, including gas-drag, pull-down,
and three-body capture, convincingly fit the group characteristics of the
irregular satellites. The sources of the satellites also remain unidentified.Comment: 51 pages, 17 figures, 5 tables, to appear in ARAA 200
The Calibration of the HST Kuiper Belt Object Search: Setting the Record Straight
The limiting magnitude of the HST data set used by Cochran et al. (1995) to
detect small objects in the Kuiper belt is reevaluated, and the methods used
are described in detail. It is shown, by implanting artificial objects in the
original HST images, and re-reducing the images using our original algorithm,
that the limiting magnitude of our images (as defined by the 50% detectability
limit) is . This value is statistically the same as the value found in
the original analysis. We find that of the moving Kuiper belt objects
with are detected when trailing losses are included. In the same data
in which these faint objects are detected, we find that the number of false
detections brighter than is less than one per WFPC2 image. We show
that, primarily due to a zero-point calibration error, but partly due to
inadequacies in modeling the HST'S data noise characteristics and Cochran et
al.'s reduction techniques, Brown et al. 1997 underestimate the SNR of objects
in the HST dataset by over a factor of 2, and their conclusions are therefore
invalid.Comment: Accepted to ApJ Letters; 10 pages plus 3 figures, LaTe
Extreme Kuiper Belt Object 2001 QG298 and the Fraction of Contact Binaries
Extensive time-resolved observations of Kuiper Belt object 2001 QG298 show a
lightcurve with a peak-to-peak variation of 1.14 +-0.04 magnitudes and
single-peaked period of 6.8872 +- 0.0002 hr. The mean absolute magnitude is
6.85 magnitudes which corresponds to a mean effective radius of 122 (77) km if
an albedo of 0.04 (0.10) is assumed. This is the first known Kuiper Belt object
and only the third minor planet with a radius > 25 km to display a lightcurve
with a range in excess of 1 magnitude. We find the colors to be typical for a
Kuiper Belt object (B-V = 1.00 +- 0.04, V-R = 0.60 +- 0.02) with no variation
in color between minimum and maximum light. The large light variation,
relatively long double-peaked period and absence of rotational color change
argue against explanations due to albedo markings or elongation due to high
angular momentum. Instead, we suggest that 2001 QG298 may be a very close or
contact binary similar in structure to what has been independently proposed for
the Trojan asteroid 624 Hektor. If so, its rotational period would be twice the
lightcurve period or 13.7744 +- 0.0004 hr. By correcting for the effects of
projection, we estimate that the fraction of similar objects in the Kuiper Belt
is at least 10% to 20% with the true fraction probably much higher. A high
abundance of close and contact binaries is expected in some scenarios for the
evolution of binary Kuiper Belt objects.Comment: 15 text pages,6 figures(Color),5 Tables, Accepted to AJ for May 200
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