This issue of the newsletter unfortunately was delayed by more than a month due to unusually intense time demands on me by other projects. Rather than compress the schedule for the next issue, I will just go with the flow and shift the regular schedule to the right by a month. The next issue will be published in June, and announcements for submissions will be sent out at the end of May.
There were 18 new TNO discoveries announced since the previous issue of Distant EKOs:
2005 EB318, 2005 EC318, 2005 ED300, 2005 EE296, 2005 EF298, 2005 EF304, 2005 EH305, 2005 EJ300, 2005 EK298, 2005 EM303, 2005 EN302, 2005 EO296, 2005 EO297, 2005 EO302, 2005 EO304, 2005 EP296, 2005 EX297, 2005 EZ296
and 2 new Centaur/SDO discoveries:
2005 EB299, 2005 EZ300
Reclassified objects:
2004 TF282 (TNOSDO)
Current number of TNOs: 865 (and Pluto & Charon, and 12 other TNO binary companions)
Current number of Centaurs/SDOs: 152
Current number of Neptune Trojans: 1
Out of a total of 1018 objects:
494 have measurements from only one opposition
418 of those have had no measurements for more than a year
206 of those have arcs shorter than 10 days
(for more details, see:
http://www.boulder.swri.edu/ekonews/objects/recov_stats.gif)
The Deep Ecliptic Survey (DES)--a search optimized for the discovery
of Kuiper belt objects (KBOs) with the Blanco and Mayall 4 m
telescopes at the Cerro Tololo Inter-American Observatory and Kitt
Peak National Observatory--has covered 550 square degrees from its
inception in 1998 through the end of 2003. This survey has a mean 50%
sensitivity at VR magnitude 22.5. We report here the discoveries of
320 designated KBOs and Centaurs for the period 2000 March through
2003 December and describe improvements to our discovery and recovery
procedures. Our data and the data products needed to reproduce our
analyses in this paper are available through the NOAO survey
database. Here we present a dynamical classification scheme, based on
the behavior of orbital integrations over 10 Myr. The dynamical
classes, in order of testing, are ``Resonant,'' ``Centaur,''
``Scattered-Near,'' ``Scattered-Extended,'' and ``Classical.'' (These
terms are capitalized when referring to our rigorous definitions.) Of
the 382 total designated KBOs discovered by the DES, a subset of 196
objects have sufficiently accurate orbits for dynamical
classification. Summary information is given for an additional 240
undesignated objects also discovered by the DES from its inception
through the end of 2003. The number of classified DES objects
(uncorrected for observational bias) are Classical, 96; Resonant, 54;
Scattered-Near, 24; Scattered-Extended, 9; and Centaur, 13. We use
subsets of the DES objects (which can have observational biases
removed) and larger samples to perform dynamical analyses on the
Kuiper belt. The first of these is a determination of the Kuiper belt
plane (KBP), for which the Classical objects with inclinations less
than 5 from the mean orbit pole yield a pole at
R.A.=273.92
0.62 degrees and decl.=66.70.20 degrees (J2000),
consistent with the invariable plane of the solar system. A general
method for removing observational biases from the DES data set is
presented and used to find a provisional magnitude distribution and
the distribution of orbital inclinations relative to the KBP. A
power-law model fit to the cumulative magnitude distribution of all
KBOs discovered by the DES in the VR filter yields an index of
0.860.10 (with the efficiency parameters for the DES fitted
simultaneously with the population power law). With the DES
sensitivity parameters fixed, we derive power-law indices of
0.740.05, 0.520.08, and 0.740.15, respectively, for the
Classical, Resonant, and Scattered classes. Plans for calibration of
the DES detection efficiency function and DES magnitudes are
discussed. The inclination distribution confirms the presence of
``hot'' and ``cold'' populations; when the geometric 
factor
is removed from the inclination distribution function, the cold
population shows a concentrated ``core'' with a full width at
half-maximum of approximately 4.6 degrees, while the hot population
appears as a ``halo,'' extending beyond 30 deg. The inclination
distribution is used to infer the KBO distribution in the sky, as a
function of latitude relative to the KBP. This inferred latitude
distribution is reasonably consistent with the latitude distribution
derived from direct observation, but the agreement is not perfect. We
find no clear boundary between the Classical and Scattered classes
either in their orbital inclinations with respect to the KBP or in
their power-law indices in their respective magnitude
distributions. This leaves open the possibility that common processes
have shaped the distribution of orbital parameters for the two
classes.
Published in: The Astronomical Journal, 129, 1117 (2005 February)
For preprints, contact jle@mit.edu
In the transneptunian classical region (42 AU<a<48 AU) it is
observed an unexpected orbital excitation in eccentricity and
inclination, dynamically distinct populations and the presence of
chaotic regions. For instance, the 7:4 mean motion resonance (
AU) appears to have been causing unique dynamical excitation
according to observational evidences. Namely, an apparent shallow gap
in number density and anomalies in the color distribution, both
features enhanced near the 7:4 mean motion resonance location. In
order to investigate the resonance dynamics, we present extensive
computer simulation results totalizing almost 10000 test particles
under the effect of the four giant planets for the age of the solar
system. A chaotic diffusion experiment was also performed to follow
tracks in phase space over 4-5 Gyr. The 7:4 mean motion resonance is
weakly chaotic causing irregular eccentricity and inclination
evolution for billion of years. Most 7:4 resonant particles suffered
significant eccentricities and/or inclinations excitation, an outcome
shared even by those located in the vicinity of the
resonance. Particles in stable resonance locking are rare and usually
had 0.25<e<0.3. For other regions, 7:4 resonants had quite large
mobility in phase space typically leaving the resonance (and being
scattered) after reaching a critical 
. The escape happened
in 108-109 yr time scales. Concerning the inclination dependence
for 7:4 resonants, we found strong instability islands for
approximately i>10 degrees. Taking into account those particles still
locked in the resonance at the end of the simulations, we determined a
retainability of 12-15% for real 7:4 resonant TNOs. Lastly, our
results demonstrate that classical TNOs associated with the 7:4 mean
motion resonance have been evolving continuously until present with
non-negligible mixing of populations.
To appear in: Planetary and Space Science
For preprints, contact patryk@kobe-u.ac.jp
or on the web at
http://harbor.scitec.kobe-u.ac.jp/~patryk/index-uk.html
We present a statistical model for estimating the effects of stellar
encounters on orbits in the outer Solar System, focussing on the
scattered disk at
AU from the Sun. We describe a Monte
Carlo simulation using those results and apply it to the evolution of
the scattered disk over 4 Gyr, finding that a final perihelion
distance distribution with an extended tail reaching to very large
values is to be expected. This would likely result from a single close
stellar encounter, in agreement with the conclusion by Morbidelli &
Levison (2004). We estimate that the newly discovered minor planet
(90377) Sedna may be a typical representative of such an extended
scattered disk and that a few more objects of the same size may reside
at similar heliocentric distances. There is a possibility that the
bulk of the population, which should have smaller perihelion
distances, contains some very large objects that may have contributed
to sculpting the Kuiper Belt. We also find that the creation of an
extended scattered disk by a stellar encounter should have been
accompanied by a huge influx of large objects into the inner Solar
System, but the timing of the encounter is constrained by the fact
that the scattered disk must still have been quite massive. Thus it
likely happened long before the purported late heavy bombardment of
the terrestrial planets.
Published in: Astronomy & Astrophysics, 428, 637 (2004 December)
For preprints, contact hans.rickman@astro.uu.se
or on the web at
http://www.edpsciences.org/articles/aa/abs/2004/47/aa1109/aa1109.html
Our planetary system is embedded in a small-body disk of asteroids and comets, vestigial remnants of the original planetesimal population that formed the planets. Once formed, those planets dispersed most of the remaining small bodies. Outside of Neptune, this process has left our Kuiper belt and built the Oort cloud, as well as emplacing comets into several other identifiable structures. The orbits in these structures indicate that our outer solar system's comet disk was shaped by a variety of different physical processes, which teach us about how the giant planets formed. Recent work has shown that the scattered disk is the most likely source of short-period comets. Moreover, a growing body of evidence indicates that the sculpting of the Kuiper belt region may have involved large-scale planetary migration, the presence of other rogue planetary objects in the disk, and/or the close passage of other stars in the Sun's birth cluster.
Published in: Science, 307, 71 (2005 January 07)
For preprints, contact gladman@astro.ubc.ca
or on the web at
http://www.sciencemag.org/cgi/content/abstract/307/5706/71
Discovery of transneptunian object (TNO) satellites and determination of their orbits has recently enabled estimation of the size and albedo of several small TNOs, extending the size range of objects having known size and albedo down into the sub-100 km range. In this paper we compute albedo and size estimates or limits for 20 TNOs, using a consistent method for all binary objects and a consistent method for all objects having reported thermal fluxes. As is true for larger TNOs, the small objects show a remarkable diversity of albedos. Although the sample is limited, there do not yet appear to be any trends relating albedo to other observable properties or to dynamical class, with the possible exception of inclination. The observed albedo diversity of TNOs has important implications for computing the size-frequency distribution, the mass, and other global properties of the Kuiper belt derived from observations of objects' apparent magnitudes and may also point the way toward an improved compositional taxonomy based on albedo in addition to color.
To appear in: Icarus
For preprints, contact W.Grundy@lowell.edu
or on the web at: http://arxiv.org/abs/astro-ph/0502229
Recent observations of the Edgeworth-Kuiper belt object (EKBO)
2001 QG298 (Sheppard & Jewitt 2004) have shown that the
lightcurve of this object has a very large amplitude
(1.140.04 mag), indicating that it is either of an elongated
shape or of a binary structure with two components of similar sizes
nearly in contact with each other. On the basis of these interesting
published data, we employed Roche binary lightcurve simulations to
construct a shape model of EKBO 2001 QG298. The shape
parameters of the best-fitted model were
260(164) x 205(130)
x 185(116) km for the primary, and
265(168) x 160(102)
x 150(94) km for the secondary in the case of an albedo of
0.04(0.10). An additional result of this calculation is that the
average bulk density of the contact binary system could be estimated
to be 630 kg m-3. This value is similar to that of several icy
moons of Saturn with a diameter of less than 200 km. We have also used
the Jacobi ellipsoidal approximation to compute the shape of one of
the largest EKBOs, Varuna. The corresponding shape parameters are
a
: b : c = 1.00 : 0.76 : 0.50. The lower limit of the bulk density is
kg m-3. These results are in good agreement with
the published values of Jewitt and Sheppard (2002), and are consistent
with their suggestion that larger icy bodies have higher densities
(Sheppard & Jewitt 2002).
Published in: Publications of the Astronomical Society of Japan, 56, 1099
For preprints, contact shigeru@astro.ncu.edu.tw
or on the web at
http://pasj.asj.or.jp/v56/n6/560614/560614a.html
The observed size distribution of Kuiper belt objects (KBOs)--small
icy and rocky Solar System bodies orbiting beyond Neptune--is well
described by a power law at large KBO sizes. However, recent work by
Bernstein et al. (2004, Astron. J. 128, 1364-1390) indicates that the
size distribution breaks and becomes shallower for KBOs smaller than about
70 km in size. Here we show that we expect such a break at KBO radius
40 km since destructive collisions are frequent for smaller KBOs.
Specifically, we assume that KBOs are gravity-dominated bodies with
negligible material strength. This gives a power-law slope 
,
where the number N>r of KBOs larger than a size r is given by
; the break location follows from this slope
through a self-consistent calculation. The existence of this break, the
break's location, and the power-law slope we expect below the break are
consistent with the findings of Bernstein et al. (2004, Astron. J. 128, 1364-1390). The agreement with observations indicates that KBOs as small as
40 km are effectively strengthless.
Published in: Icarus, 173, 342 [2005 February]
For preprints, contact mpan@astro.caltech.edu
Pluto and its moon, Charon, are the most prominent members of the Kuiper belt, and their existence holds clues to outer solar system formation processes. Here, hydrodynamic simulations are used to demonstrate that the formation of Pluto-Charon by means of a large collision is quite plausible. I show that such an impact probably produced an intact Charon, although it is possible that a disk of material orbited Pluto from which Charon later accumulated. These findings suggest that collisions between 1000-kilometer-class objects occurred in the early inner Kuiper belt.
Published in: Science, 307, 546 [2005 January 28]
For preprints, contact robin@boulder.swri.edu
or on the web at
http://www.boulder.swri.edu/~robin/rcpapers.html
We have carried out infrared high-resolution spectroscopy of the Pluto-Charon system in the L band with the adaptive optics system on the Subaru telescope. The spectrum is dominated by the strong and broad absorption features of methane but includes some additional features. Comparing the spectrum with model calculations, we suggest that absorption features around 3.1, 3.2, and 3.35 mum could be an indication of nonmethane hydrocarbons on Pluto's uppermost surface. Implications of the estimated mass ratio between hydrocarbons for the formation and evolution of Pluto are discussed.
Published in: The Astrophysical Journal Letters, 618, L57 [2005 January]
For preprints, contact takanori@eps.s.u-tokyo.ac.jp
We have observed the 2002 August 21 occultation by Pluto of the
R=15.7 mag star P131.1, using 0.5 s cadence observations in integrated
white light with the Williams College frame-transfer, rapid-readout
CCD at the 2.24 m University of Hawaii telescope. We detected an
occultation that lasted 5 minutes, 
s between half-light
points. The ``kinks'' in the ingress and egress parts of the curve
that were apparent in 1988 had become much less pronounced by the
time of the two 2002 occultations that were observed, indicating a
major change in the structure of Pluto's atmosphere. Analysis of
our light curves shows that the pressure in Pluto's atmosphere has
increased at all the altitudes that we probed. Essentially, the
entire pressure scale has moved up in altitude, increasing by a
factor of 2 since 1988. Spikes in our light curve reveal vertical
structure in Pluto's atmosphere at unprecedentedly high resolution.
We have confirmation of our spikes at lower time resolution as part
of observations of the emersion made at 1.4 s and 2.4 s cadence
with the 3.67 m AEOS telescope on Maui.
Published in: The Astronomical Journal, 129, 1718 [2005 March]
The problem of accretion in the Trojan 1:1 resonance is akin to the standard
problem of planet formation, transplanted from a star-centered disk
to a disk centered on the Lagrange point.
The newly discovered class of Neptune Trojans
promises to test theories of planet formation by coagulation.
Neptune Trojans resembling the prototype
2001 QR322 (``QR'')--whose radius of 100 km
is comparable to that of the largest Jupiter Trojan--may
outnumber their Jovian counterparts by a factor
of 10. We develop and test three theories for the origin
of large Neptune Trojans: pull-down
capture, direct collisional emplacement, and in situ accretion.
These theories are staged
after Neptune's orbit anneals: after dynamical friction
eliminates any large orbital eccentricity and after the planet
ceases to migrate. We discover that seeding the 1:1 resonance
with debris from planetesimal collisions and having the seed
particles accrete in situ naturally reproduces the inferred
number of QR-sized Trojans.
We analyze accretion in the Trojan sub-disk by applying
the two-groups method, accounting for kinematics specific to
the resonance. We find that a
Trojan sub-disk comprising decimeter-sized seed particles
and having a surface density 10-3 that
of the local minimum-mass disk produces
10 QR-sized objects in 1 Gyr, in accord with observation.
Further growth is halted by collisional diffusion of seed particles
out of resonance. In our picture, the number and sizes of the largest
Neptune Trojans represent the unadulterated outcome
of dispersion-dominated, oligarchic accretion.
Large Neptune Trojans, perhaps the most newly accreted
objects in our Solar System, may today have a dispersion
in orbital inclination of less than 10 degrees,
despite the existence of niches of stability at higher
inclinations. Such a vertically thin disk, born of a dynamically cold
environment necessary for accretion, and raised in minimal contact
with external perturbations, contrasts with the thick
disks of other minor body belts.
To appear in: The Astrophysical Journal
For preprints, contact echiang@astron.berkeley.edu
or on the web at
http://astron.berkeley.edu/~echiang/ppp/ppp.html
New Horizons Pluto-Kuiper Belt Mission: Design and Simulation of the Pluto-Charon Encounter
Yanping Guo1 and Robert W. Farquhar1
1 Applied Physics Laboratory, Johns Hopkins University, 11100 Johns Hopkins Road, Laurel, MD 20723-6099, USA
Published in: Acta Astronautica, 56, 421 (2005 February)
Submillimeter Images of a Dusty Kuiper Belt Around eta Corvi
M.C.ÊWyatt1, J.S.ÊGreaves2 W.R.F.ÊDent1, and I.ÊM.ÊCoulson3
1 UK Astronomy Technology Centre, Royal Observatory,
Edinburgh EH9 3HJ, UK
2 School of Physics and Astronomy, University of St. Andrews,
North Haugh, St. Andrews KY16 9SS, UK
3 Joint Astronomy Centre, 660 North A'ohoku Place, Hilo, HI 96720, USA
Published in: The Astrophysical Journal, 620, 492 (2005 February 10)
We accept submissions for the following sections:
Distant EKOs is not a refereed publication, but is a tool for furthering communication among people interested in Kuiper belt research. Publication or listing of an article in the Newsletter or the web page does not constitute an endorsement of the article's results or imply validity of its contents. When referencing an article, please reference the original source; Distant EKOs is not a substitute for peer-reviewed journals.
