Subsequent issues of the Distant EKOs newsletter no longer will be mailed out in LaTeX format. Starting with the January 2009 issue, future mailings of issues will consist of a brief, plain-text format table of contents and a link to the webpage where the newsletter is available in several formats: HTML, PDF, PostScript, and LaTeX. I hope this change will not cause problems for any subscribers, since all formats will still be easily available via a URL in the e-mail.
In an experiment that I hope will catch on for many more astronomical meetings, presentations at this year's DPS meeting in Ithaca were streamed live on the web. Also, the AAS plans to permanently archive (online) the webstreamed presentations. Details on how to access the archived presentations will be provided on the DPS web site in the near future.
Benecchi et al. report in IAUC 8998 that TNO 1998 WV24 is a binary.
Observations with HST show a separation of 0.051 arcsec (
1400 km),
with the secondary being 0.3 mag fainter than the primary.
IAUC: http://cfa-www.harvard.edu/iauc/08900/08998.html
There were 6 new TNO discoveries announced since the previous issue of Distant EKOs:
2007 TQ436, 2007 BO81, 2007 CJ66, 2007 CK66, 2008 AP118, 2008 AQ118
and 4 new Centaur/SDO discoveries:
2007 TR436, 2008 QD4, 2008 SJ236, 2008 UZ6
Objects recently assigned names:
2003 EL61 = Haumea
Current number of TNOs: 1090 (including Pluto)
Current number of Centaurs/SDOs: 237
Current number of Neptune Trojans: 6
Out of a total of 1333 objects:
564 have measurements from only one opposition
543 of those have had no measurements for more than a year
287 of those have arcs shorter than 10 days
(for more details, see:
http://www.boulder.swri.edu/ekonews/objects/recov_stats.gif)
The study of binary Kuiper Belt objects help probe the dynamic
conditions present during planet formation in the Solar System. We
report on the mutual-orbit determination of 2001 QW322, a Kuiper Belt binary
with a very large separation whose properties challenge binary-formation
and evolution theories. Six years of tracking indicate that the binary's
mutual orbit period is 
25-30 years, that the orbit pole is
retrograde and inclined 50-62
from the ecliptic plane, and,
most surprisingly, that the mutual orbital eccentricity is < 0.4. The
semimajor axis of 105,000-135,000 km is 10 times that of other
near-equal mass binaries. Because this weakly bound binary is prone to
orbital disruption by interlopers, its lifetime in its present state is
likely less than 1 Gy.
Published in: Science, 322, 432 (2008 October 17)
For preprints, contact petit@obs-besancon.fr
We report resolved photometry of the primary and secondary components of 23 transneptunian binaries obtained with the Hubble Space Telescope. V-I colors of the components range from 0.7 to 1.5 with a median uncertainty of 0.06 magnitudes. The colors of the primaries and secondaries are correlated with a Spearman rank correlation probability of 99.99991%, 5 sigma for a normal distribution. Fits to the primary vs. secondary colors are identical to within measurement uncertainties. The color range of binaries as a group is indistinguishable from that of the larger population of apparently single transneptunian objects. Whatever mechanism produced the colors of apparently single TNOs acted equally on binary systems. The most likely explanation is that the colors of transneptunian objects and binaries alike are primordial and indicative of their origin in a locally homogeneous, globally heterogeneous protoplanetary disk.
To appear in: Icarus
Preprints on the web at http://arxiv.org/abs/0811.2104
We present new solar phase curve observations of the 2003 EL61
collisional family showing that all the members have light-scattering
properties similar to the bright icy satellites of the giant planets and
dwarf planets. Compared with other Kuiper Belt objects (KBOs), the five
family members we observe (2003 EL61, 2002 TX300, 2003 OP32, 2005 RR43,
and 1995 SM55) have conspicuously neutral color (V-I = 0.6-0.8 mag)
and flat phase curves at small phase angles (phase coefficients of
0.0-0.1 mag deg-1). Comparing the phase curves we observe for
other icy KBOs with the phase curves of icy satellites, we find that the
flat phase curves of the 2003 EL61 family are an indication that they
have high albedo surfaces coated with fresh ice in the last
100 Myr. We examine possible resurfacing processes and find none
that are plausible. To avoid the influence of cosmic radiation that
darkens and reddens most icy surfaces on times scales 100 Myr, the
family members must be unusually depleted in carbon, or the collision
that created the family occurred so recently that the parent body and
fragments have not had time to darken. We also find a rotation period of
4.854 (+/-0.003) h with amplitude 0.26 (+/-0.04) mag for 2003 OP32.
Published in: The Astronomical Journal, 136, 1502 (2008 October)
The outcome of collisions between small icy bodies, such as Kuiper belt objects, is poorly understood and yet a critical component of the evolution of the trans-Neptunian region. The expected physical properties of outer solar system materials (high porosity, mixed ice-rock composition, and low material strength) pose significant computational challenges. We present results from catastrophic small body collisions using a new hybrid hydrocode to N-body code computational technique. This method allows detailed modeling of shock propagation and material modification as well as gravitational reaccumulation. Here, we consider a wide range of material strengths to span the possible range of Kuiper belt objects. We find that the shear strength of the target is important in determining the collision outcome for 2 to 50-km radius bodies, which are traditionally thought to be in a pure gravity regime. The catastrophic disruption and dispersal criteria, Q*D, can vary by up to a factor of three between strong crystalline and weak aggregate materials. The material within the largest reaccumulated remnants experiences a wide range of shock pressures. The dispersal and reaccumulation process results in the material on the surfaces of the largest remnants having experienced a wider range of shock pressures compared to material in the interior. Hence, depending on the initial structure and composition, the surface materials on large, reaccumulated bodies in the outer solar system may exhibit complex spectral and albedo variations. Finally, we present revised catastrophic disruption criteria for a range of impact velocities and material strengths for outer solar system bodies.
To appear in: Icarus
For preprints, contact z.m.leinhardt@damtp.cam.ac.uk
or on the web at http://www.shock.eps.harvard.edu/preprints/
In this Note, I present first-order scaling calculations to examine the efficacy of impacts by Kuiper Belt debris in causing regolith exchange between objects in the Pluto system. It is found that ejecta can escape Nix and Hydra with sufficient velocity to reach one another, as well as Charon, and even Pluto. The degree of ejecta exchanged between Nix and Hydra is sufficient to cover these bodies with much more material than is required for photometrically change. In specific, Nix and Hydra may have exchanged as up to 10s of meters of regolith, and may have covered Charon to depths up to 14 centimeters with their ejecta. Pluto is likely unaffected by most Nix and Hydra ejecta by virtue of a combination of dynamical shielding from Charon and Pluto's own annual atmospheric frost deposition cycle. As a result of ejecta exchange between Nix, Hydra, and Charon, these bodies are expected to evolve their colors, albedos, and other photometric properties to be self similar. These are testable predictions of this model, as is the prediction that Nix and Hydra will have diameters near 50 km, owing to having a Charon-like albedo induced by ejecta exchange. As I discuss, this ejecta exchange process can also be effective in many KBOs and asteroids with satellites, and may be the reason that very many KBO and asteroid satellite systems have like colors.
To appear in: Icarus
For preprints, contact alan@boulder.swri.edu
or on the web at http://dx.doi.org/10.1016/j.icarus.2008.10.006
km
We have performed a survey of the Kuiper covering 
a square
degree of the sky using Suprime-cam on the Subaru telescope, to a
limiting magnitude of
and have found 36 new KBOs.
We have confirmed that the luminosity function of the Kuiper belt must
break as previously observed (Bernstein et al. 2004; Fuentes & Holman
2008). We find that the luminosity function is consistent with that
observed from a size distribution with large object power-law slope
that breaks to a slope 
at object diameter
km assuming 6% albedos. We have found no conclusive
evidence that the size distribution of KBOs with inclinations i<5 is
different than that of those with i>5. We discuss implications of this
measurement for early accretion in the outer solar system and Neptune
migration scenarios.
To appear in: The Astronomical Journal
For preprints, contact fraserw@gps.caltech.edu
or on the web at http://arxiv.org/abs/0810.2296
Results from the first two years of data from the Taiwanese-American
Occultation Survey (TAOS) are presented. Stars have been monitored
photometrically at 4 Hz or 5 Hz to search for occultations by small
(3 km) Kuiper Belt Objects (KBOs). No statistically significant
events were found, allowing us to present an upper bound to the size
distribution of KBOs with diameters 0.5 km <D< 28 km.
Published in: The Astrophysical Journal Letters, 685, L157 (2008 October 1)
For preprints, contact s1249001@cc.ncu.edu.tw
or on the web at http://arxiv.org/abs/0808.2051
The knowledge of the rotational periods of the small bodies in the
outer Solar System is a useful tool
for retrieving information on the internal structure of the observed objects
and for having hints on the collisional evolution state of the whole
population.
In order to investigate the physical nature of Centaurs and TNOs,
we analysed the rotational properties of a selected sample.
Photometric observations of 2 Centaurs (12929 1999 TZ1 and
95626 2002 GZ32), and 5 Trans-Neptunian Objects (42355 Typhon,
47932 2000 GN171, 65489 Ceto,
90568 2004 GV9, and 120132 2003 FY128)
were carried out with the New Technology Telescope (NTT) at the European
Southern Observatory La Silla (Chile)
in the framework of the ESO Large Programme 178.C-0036 (PI. M.A. Barucci).
These observations allow us to estimate the rotational rate of three
objects, to confirm previously published periods of two bodies, and to have
the first single night lightcurves of 42355 Typhon and
120132 2003 FY128.
These data allow us to improve the available sample of determined
rotational periods of TNOs and Centaurs.
For 5 out of the 7 observed objects
we have estimated the axis ratio a/b, hence the density.
Our new results seem to
confirm the density/dimension trend, found by Sheppard et al. (2008),
with larger (brighter) objects having higher densities.
Published in: Astronomy and Astrophysics, 490, 829 (2008 November)
For preprints, contact dotto@mporzio.astro.it
We collect well-measured opposition surge properties for many icy bodies
orbiting the Sun (mostly from our own observations) plus for many icy
moons, resulting in a data base of surface and orbital properties for 52
icy bodies. (1) We put forward four criteria for determining whether the
surge is being dominated by shadow hiding (SH) or coherent backscattering
(CB) based on readily measured quantities. The CB surge mechanism
dominates if the surge is color dependent, the phase curve is steeper than
0.04 mag deg-1, the phase curve shape matches the CB model of Hapke,
or if the albedo is higher than roughly 40%. (2) We find that virtually
all of our sample have their phase curves dominated by CB at low phase
angles. (3) We present a graphical method to determine the Hapke surge
parameters BC0 and hC. (4) The Kuiper Belt Objects (KBOs) and
Centaurs have relatively high surge amplitudes,
and
widths with 
degrees. (5) We find highly significant but
loose correlations between surge properties and the colors, albedos, and
inclinations. We interpret this as young surfaces tending to have low
surge slopes, high albedo, and gray colors. (6) Nereid has its surface
properties similar to other icy moons and greatly different from KBOs and
Centaurs, so we conclude that Nereid is likely a nearly-ejected inner
Neptunian moon rather than a captured KBO.
To appear in: The Astronomical Journal
For preprints, contact schaefer@lsu.edu
or on the web at http://arxiv.org/abs/0810.0965
Trans-Neptunian objects (TNOs) contain the most primitive and thermally least-processed materials from the early accretional phase of the solar system. They allow us to study interrelations between various classes of small bodies, their origin and evolution.
Using FORS1 of the ESO VLT, we have obtained linear-polarization
measurements in the Bessell R filter for five TNOs at different
values of their phase angle (i.e., the angle between the Sun, the
object, and the Earth). Due to the large distance of the targets
(> 30AU), the observed range of phase angles is limited to about
.
We have analyzed our new observations of five TNOs, and those of
another four TNOs obtained in previous works, and discovered that
there exist two classes of objects that exhibit different
polarimetric behaviour. Objects with a diameter 
km, such
as, e.g., Pluto and Eris, show a small polarization in the scattering
plane (
%) which slowly changes in the observed phase angle
range. In smaller objects such as, e.g., Ixion and Varuna, linear
polarization changes rapidly with the phase angle, and reaches 
% (in the scattering plane) at phase angle 
. The
larger objects have a higher albedo than the smaller ones, and have
the capability of retaining volatiles such as CO, N2 and CH4. Both
of these facts can be linked to their different polarimetric
behaviour compared to smaller objects.
In spite of the very limited range of observable phase angles,
ground-based polarimetric observations are a powerful
tool to identify different properties of the surfaces of TNOs. We
suggest that a single polarimetric observation at phase angle 
allows one to determine whether the target albedo is low or
high.
To appear in: Astronomy & Astrophysics
For preprints, contact sba@arm.ac.uk
or on the web at http://star.arm.ac.uk/preprints/
We describe optical spectroscopic observations of the icy dwarf planet Eris with the 6.5 meter MMT telescope and the Red Channel Spectrograph. We report a correlation, that is at the edge of statistical significance, between blue shift and albedo at maximum absorption for five methane ice bands. We interpret the correlation as an increasing dilution of methane ice with another ice component, probably nitrogen, with increasing depth into the surface.
We suggest a mechanism to explain the apparent increase in nitrogen with depth. Specifically, if we are seeing Eris 50 degrees from pole-on (Brown and Schaller, 2008), the pole we are seeing now at aphelion was in winter darkness at perihelion. Near perihelion, sublimation could have built up atmospheric pressure on the sunlit (summer) hemisphere sufficient to drive winds toward the dark (winter) hemisphere, where the winds would condense. Because nitrogen is more volatile and scarcer than methane, it sublimated from the sunlit hemisphere relatively early in the season, so the early summer atmosphere was nitrogen rich, and so was the ice deposited on the winter pole. Later in the season, much of the nitrogen was exhausted from the summer pole, but there was plenty of methane, which continued to sublimate. At this point, the atmosphere was more depleted in nitrogen, as was the ice freezing out on top of the earlier deposited nitrogen rich ice.
Our increasing nitrogen abundance with depth apparently contradicts the Licandro et al. (2006) result of a decreasing nitrogen abundance with depth. A comparison of observational, data reduction, and analysis techniques between the two works, suggests the difference between the two works is real. If so, we may be witnessing the signature of weather on Eris. The work reported here is intended to trigger further observational effort by the community.
To appear in: Icarus
For preprints, contact Stephen.Tegler@nau.edu
or on the web at http://arxiv.org/abs/0811.0825
Pluto occultations are historically rare events, having been observed in
1988, 2002, 2006, and, as Pluto moves into the crowded Galactic plane,
on several occasions in 2007. Here we present six results from our
observations of the 2006 June 12 event from several sites in Australia
and New Zealand. First, we show that Pluto's 2006 bulk atmospheric
column abundance, as in 2002, is over twice the value measured in 1988,
implying that nitrogen frost on Pluto's surface is 1.2-1.7 K warmer in
2006 than 1988 despite a 9% drop in incident solar flux. We measure a
half-light shadow radius of 1216
8.6 km in 2006, nominally larger
than published values of 121316 km measured in 2002. Given the
current error bars, this latest half-light radius cannot discriminate
between continued atmospheric growth or shrinkage, but it rules out
several of the volatile transport scenarios modeled by Hansen & Paige.
Second, we resolve spikes in the occultation light curve that are
similar to those seen in 2002 and model the vertical temperature
fluctuations that cause them. Third, we show that Pluto's upper
atmosphere appears to hold a steady temperature of 100 K, as
predicted from the methane thermostat model, even at latitudes where the
methane thermostat is inoperative. This implies that energy transport
rates are faster than radiational cooling rates. Fourth, this
occultation has provided the first significant detection of a
non-isothermal temperature gradient in Pluto's upper atmosphere also
reported by Elliot et al., possibly the result of CO gas in Pluto's
upper atmosphere. Fifth, we show that a haze-only explanation for
Pluto's light curve is extremely unlikely; a thermal inversion is
necessary to explain the observed light curve. And sixth, we derive an
upper limit for the haze optical depth of 0.0023 in the zenith direction
at average CCD wavelengths.
Published in: The Astronomical Journal, 136, 1757 (2008 November)
Observations of the 2007 March 18 occultation of the star P445.3 (2UCAC
25823784; R=15.3) by Pluto were obtained at high time resolution at five
sites across the western United States and reduced to produce light
curves for each station using standard aperture photometry. Global
models of Pluto's upper atmosphere are fit simultaneously to all
resulting light curves. The results of these model fits indicate that
the structure of Pluto's upper atmosphere is essentially unchanged since
the previous occultation observed in 2006, leading to a well constrained
measurement of the atmospheric half-light radius at 12915 km, and
confirm that the significant increase in atmospheric pressure detected
between 1988 and 2002 has ceased (Elliot et al. 2007). Inversion of the
MMTO light curves with unprecedented signal-to-noise ratios reveals
significant oscillations in the number density, pressure, and
temperature profiles of Pluto's atmosphere. Detailed analysis of this
highest resolution light curve indicates that these variations in
Pluto's upper atmospheric structure exhibit a previously unseen
oscillatory structure with strong correlations of features among
locations separated by almost 1200 km in Pluto's atmosphere. Thus, we
conclude that these variations are caused by some form of large-scale
atmospheric waves. Interpreting these oscillations as Rossby
(planetary) waves allows us to establish lower and upper limits of 2 and
30 m/s respectively for horizontal wind speeds in the sampled region
(radius 1340-1460 km) of Pluto's upper atmosphere.
Published in: The Astronomical Journal, 1261, 510 (2008 October)
For preprints, contact mjperson@mit.edu
Context. One of the main scientific objectives of NASA's New
Horizons mission is to map the icy surface compositions of Pluto and its
moon Charon. The encounter will be in 2015. Meanwhile remote
observations from earth and space are the most suitable means to enhance
further our knowledge of the Pluto/Charon system.
Aims. We intend to assist the New Horizons mission by improving
our knowledge of Pluto's and Charon's surface compositions.
Specifically, we extend the wavelength coverage of the surface
spectroscopy beyond the K band, with the goal to detect further
surface ice absorption bands predicted from the models that are based on
the available JHK spectra, and to search for signatures of yet unknown
ices. In particular we aim to resolve the binary system Pluto/Charon and
to obtain, for the first time, spectra up to 5 
m of the two objects
resolved.
Methods. Spectroscopic measurements of Pluto/Charon taken with the adaptive optics instrument NACO at the ESO VLT in the interval 3-7 August 2005 were obtained. The nature and properties of the compounds present on the surface of Pluto and Charon are investigated by applying a Hapke radiative transfer model to the measured spectra.
Results. We present Pluto's reflectance spectrum in the wavelength
range (1-5) m. Apart from known and expected absorption bands of
methane ice, our Pluto spectrum reveals a new absorption band centered
near 4.6 m, not previously detected. This absorption band could be
related to the presence of CO and nitriles (compounds of C and N
connected with a triple bond). A geographic mixture of pure methane ice
with two different grain sizes, methane and CO ice diluted in nitrogen,
CH2CHCN and titan tholin gives the best fit to Pluto's spectrum,
although not in all details. Differences compared to published Pluto
spectra from 2001 taken at similar longitude could be due to a different
surface coverage in latitude or to a possible resurfacing process on
Pluto. Charon's spectrum is measured in the wavelength range
(1-4) m. The surface of Charon can be modeled by pure water ice
darkened by a spectrally neutral continuum absorber.
Published in: Astronomy & Astrophysics, 490, 365 (2008 October)
The extremely red colors of some transneptunian objects and Centaurs are not seen among the Jupiter family comets which supposedly derive from them. Could this mismatch result from sublimation loss of colorless ice? Radiative transfer models show that mixtures of volatile ice and nonvolatile organics could be extremely red, but become progressively darker and less red as the ice sublimates away.
To appear in: Icarus
Preprints at http://arxiv.org/abs/0811.2433
We studied icy CH4 and its mixtures with N2 (temperature
16-40 K), using near-IR transmittance spectroscopy (1.0-3.6 m),
and monitoring the film growth using interference patterns of two
lasers. We measured peak position, full width at half maximum, and
strengths of the methane bands, and density and real refractive index of
the icy films. Results confirm and extend but also partially contradict
previous studies on similar mixtures. Experimental data can be applied
to interpret observations of Solar System (trans-Neptunian objects) and
interstellar ices, where methane and nitrogen are believed to be
present. We predict the optical depths of two methane NIR bands in the
line of sight of some dense molecular clouds.
Published in: The Astrophysical Journal, 686, 1480 (2008 October 20)
For preprints, contact rosario.brunetto@ias.u-psud.fr
Context. Minor bodies in the outer solar system show a wide variety of
spectral colors related to both composition and surface processing, e.g.
cosmic ion irradiation.
Aims. We investigate the effect of an irradiation mantle on the
reflectance spectrum in the V-NIR (visible-near-infrared) range. In
particular we investigate the condition needed for a weathering crust to
mask the presence of water ice.
Methods. We start from laboratory experiments of ion irradiated methane
ice to study the optical properties of the hydrocarbon residue
by-product of the space weathering process. We compare the real and
imaginary index of refraction with those of Titan and ice tholins and
with those of amorphous carbon. We use the estimated optical constants
to model a layered configuration using the Hapke theory, varying the
thickness and grain size of the modeled crust.
Results. We find that a relatively thin (tens of microns) crust of
irradiated methane by-products can mask the presence of water ice bands
in the spectrum, while a much larger layer of tholins would be required
to produce a similar effect. We also estimate the conditions for the
detection of water ice on trans-Neptunian objects (TNOs). We discuss the
results in view of the astrophysical timescale.
Published in: Astronomy & Astrophysics, 481, 879 (2008 April)
For preprints, contact rosario.brunetto@ias.u-psud.fr
A Subaru Pencil-beam Search for 
Trans-neptunian Bodies
Cesar I.Fuentes1, Matthew R.George1,2, Matthew J.Holman1
1 Harvard-Smithsonian Center for Astrophysics, 60 Garden Street, Cambridge, MA 02138, USA
2 Current Address: Department of Astronomy, University of California at Berkeley, Berkeley, CA 94720, USA
Submitted to: The Astrophysical Journal Letters
For preprints, contact cfuentes@cfa.harvard.edu
or on the web at http://arxiv.org/abs/0809.4166
Velocity-dependent Catastrophic Disruption Criteria for Planetesimals
S.T. Stewart1 and Z.M. Leinhardt2
1 Department of Earth and Planetary Sciences, Harvard University, USA
2 Department of Applied Mathematics and Theoretical Physics, Cambridge University, USA
Submitted to: Astrophysical Journal Letters
For preprints, contact sstewart@eps.harvard.edu
or on the web at http://www.shock.eps.harvard.edu/preprints/
The Department of Physics and Astronomy at Northern Arizona University (NAU) seeks an outstanding postdoctoral scholar to work with Professor David Trilling in studies of the Kuiper Belt. The ideal candidate will have a Ph.D. in astronomy, physics, planetary science, or related field, and be familiar with optical and/or infrared surveys of the Kuiper Belt and/or large observational datasets. The successful candidate will use both archival datasets and acquire new observations of the Kuiper Belt, and may also execute independent research. NAU has full competitive access to all University of Arizona Observatories (UAO) facilities, including the 6.5-meter MMT and Magellan telescopes, the 2x8.4-meter Large Binocular Telescope, and numerous smaller telescopes. Ample research and travel funds will be available.
The appointment is expected to be two years with a third year possible. NAU offers an excellent benefit package to postdoctoral scholars. Flagstaff is a beautiful town of 60,000 people nestled at the base of the San Francisco Peaks in northern Arizona. We enjoy four seasons of outdoor activities. Physics and Astronomy is a small, friendly department with emphases on both research and teaching.
To apply, please visit the NAU HR web page at
http://hr.nau.edu/m/content/view/797/550/
and reference job #557928.
Applicants should submit a CV, list of publications, a brief statement of research interests and experience, and the names and contact information of three recommenders. Applications will be considered beginning on January 15, 2009.
Northern Arizona University is a committed Equal Opportunity/Affirmative Action Institution. Women, minorities, veterans and individuals with disabilities are encouraged to apply. NAU is responsive to the needs of dual career couples.
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.
