For the numerology-inclined, the number of EKOs has passed 200 in time for the year 2000. A total of 105 EKOs and 6 Centaurs have been discovered in 1999, nearly doubling the number found in all previous years combined (and a few more 1999 discovery reports will likely trickle in during the next month or so). It is encouraging that more observing time also is being dedicated to recoveries in attempts to keep up with this phenomenal discovery rate.
There were 19 new EKO discoveries announced since the previous issue of
the Distant EKOs Newsletter:
1999 OG4, 1999 OH4, 1999 OJ4, 1999 OK4, 1999 OL4, 1999 OM4,
1999 ON4, 1999 OO4,
1999 RS214, 1999 RT214, 1999 RU214, 1999 RV214,
1999 TC36, 1999 XY143, 1999 RW214,
1999 RX214,1999 RY214, 1999 RZ214, 1999 RA215
And 1 new Centaur:
1999 XX143
Current number of EKOs: 216 (and Pluto & Charon)
Current number of Centaurs: 17
This paper reports on a series of laboratory impact experiments designed to provide basic data on how simulated Edgeworth-Kuiper belt objects (EKOs) fragment in an impact event. In September-October 1997 we carried out 20 low-velocity airgun shots at the Ames Vertical Gun Range into porous and homogeneous ice spheres using aluminum, fractured ice, and solid ice projectiles. We found that the porous ice targets behaved as strongly as solid ice in collision. Energy is apparently well dissipated by the void spaces within the target, such that these fragile ice structures respond as if they were strong in impacts. Therefore, it would appear that if EKOs are porous, they are not collisionally weak.
Also, our data show that collisional outcomes for low-velocity impacts into
ice targets depend on the type of projectile used as well as the properties of
the target. We observed that the degree of fragmentation for any given type of
target increases as the strength of the projectile increases. Aluminum
projectiles are far more damaging to the target at the same collisional energy
than solid ice projectiles, which in turn, are more damaging than fractured
ice projectiles. One possible explanation for this behavior is the variable
depth of penetration of the projectile for different cases--stronger
projectiles penetrate more deeply and couple more energy into the target than
do weak projectiles. Based on this, if we assume that there has not been
significant heating or differentiation in the Edgeworth-Kuiper (E-K) belt, the
most applicable impact strength for the low-velocity E-K belt collisions
is likely to be that derived from similar target/projectile materials impacting
each other. The laboratory data from this analysis indicate that a value for
impact strength
ergs/cm3 is appropriate for porous ice
targets impacted with solid/porous ice projectiles.
Published in: Icarus 142, 56 (1999 November)
For preprints, contact eryan@physics.nmhu.edu
We present results from our model of collision rates in the present-day
Edgeworth-Kuiper Belt and Centaur region. We have updated previous results to
allow for new estimates of the total disk population, in order to examine
surface activation and modification time scales due to cratering impacts. We
extend previous results showing that the surfaces of Edgeworth-Kuiper Belt
objects are not primordial and have been moderately to heavily reworked by
collisions. Objects smaller than about r = 2.5 km have collisional
disruption lifetimes less than 3.5 Gyr in the present-day collisional
environment and have probably been heavily damaged in their interiors by large
collisions. In the 30-50 AU region, impacts of 1 km radius comets onto
individual 100 km radius objects occur on
-
yr
time scales, cratering the surfaces of the larger objects with 
8-54
craters 6 km in diameter over a 3.5 Gyr period. Collision time scales for
impacts of 4 meter radius projectiles onto 1 km radius comets range from 3-5
yr. The cumulative fraction of the surface area of 1 and 100 km
radius objects cratered by projectiles with radii larger than 4 m ranges from a
few to a few tens percent over 3.5 Gyr. The flux of Edgeworth-Kuiper Belt
projectiles onto Pluto and Charon is also calculated and is found to be
3-5 times that of previous estimates. Our impact model is also applied
to Centaur objects in the 5-30 AU region. We find that during their dynamical
lifetimes within the Centaur region, objects undergo very little collisional
evolution. Therefore, the collisional/cratering histories of Centaurs are
dominated by the time spent in the Edgeworth-Kuiper Belt rather than the time
spent on planet-crossing orbits. Further, we find that the predominant surface
activity of Centaur objects like Chiron is most likely not impact-induced.
To appear in: Icarus
For preprints, contact durda@boulder.swri.edu
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
(
errors) and the
total mass of SKBOs to be
,
demonstrating that
the SKBOs are similar in number and mass to the Kuiper Belt inside 50
AU.
To appear in: Astrophysical Journal Letters, 529 (2000 February 1)
For preprints, contact chad@ifa.hawaii.edu
or by anonymous ftp to ftp://hubble.ifa.hawaii.edu/OUTGOING/chad/skbos/
or on the web at http://www.ifa.hawaii.edu/~chad/skbos/
We have obtained near infrared spectra of the 4 brightest known Centaurs and of
5 irregular satellites of giant planets. Many of these objects show 1.5 and 2.0
m absorption bands indicative of water ice, including 1997 CU26,
Pholus, Phoebe (S9), and Nereid (N2). The satellites of Jupiter - Elara,
Himalia, and Pasaphae (J6, J7, J8) - appear spectrally featureless, consistent
with asteroidal origins for these bodies. Phoebe's surface water ice indicates
that it formed as an icy planetesimal rather than as an asteroid.
To appear in: The Astrophysical Journal (2000 February)
Preprints on the web at http://www.gps.caltech.edu/~mbrown/papers/pubs.html
Observations have resolved the satellite Charon from its parent planet Pluto,
giving separate spectra of the two objects over from 1.0 to 2.5 m. The
spectrum of Charon is found to be different from that of Pluto, with water ice
in crystalline form covering most of the surface of the satellite. In addition,
an absorption feature in Charon's spectrum suggests the presence of ammonia
ices. Ammonia ice - water ice mixtures have been proposed as the cause of
flow-like features observed on the surfaces of many icy satellites. The
existence of such ices on Charon may indicate geological activity in the
satellite's past.
Published in: Science, 287, 107 (2000 January 7)
Preprints on the web at http://www.gps.caltech.edu/~mbrown/papers/pubs.html
We present a reflectance spectrum of 2060 Chiron over the wavelength range
1.6-2.2 m. The 2-m water ice absorption feature seen in several other
Centaurs at 
=2.03 m is identified at the 5% level below the
continuum.
Published in: Icarus, 141, 408 (1999 October)
For reprints, contact S.F.Green@ukc.ac.uk
The detection and observation of satellites of the small bodies orbiting the Sun in the outer Solar System is extremely important in order to determine the orbit and masses of the components in the binary system as well as to know their sizes to derive their mean bulk density. This note provides a formal estimation of the possible separation distances, orbital periods, and apparent brightnesses of possible satellites of the objects in the inner region of the Edgeworth-Kuiper Belt.
Published in: Icarus, 141, 420 (1999 October)
For preprints, contact tothi@konkoly.hu
Periodic orbits in the external 3:2 orbital resonance are investigated in the context of the planar, elliptic restricted three-body problem. Differential continuation is employed to determine the location of such orbits. Their stability and periods of libration around them are also computed. Stable, nearly circular orbits for hypothetical small bodies are found in extrasolar planetary systems having a giant planet on a very eccentric orbit. These orbits cross the orbit of the giant planet, but the 3:2 orbital resonance keeps them safely apart in a configuration analogous to that of Neptune and Pluto.
Published in: The Astronomical Journal, 118, 2526 (1999 November)
For preprints, contact varadi@ucla.edu
A Detection Method for the Small Kuiper Belt Objects:
The Statistical
Stellar Occultations
F. Roques1, M. Moncuquet1
1 DESPA, Observatoire de Paris, 92195 Meudon, France
Submitted to: Icarus
For preprints, contact roques@obspm.fr
Charon's First Detailed Spectra Hold Many Surprises
Eliot Young1
1 Southwest Research Institute, Suite 426, 1050 Walnut Street, Boulder, CO, 80302, USA
Published in: Science, 287, 53 (2000 January 7)
For preprints, contact efy@boulder.swri.edu
The American Astronomical Society's 195th annual meeting will be held January
11-15 in Atlanta, Georgia.
The full list of sessions can be found at:
http://www.aas.org/publications/baas/v31n5/aas195/SL.htm
Below I list some Kuiper Belt-related papers to be presented at the meeting:
Astrometric Observations of Kuiper Belt Objects
C.M. Ernst, M.J. Holman
http://www.aas.org/publications/baas/v31n5/aas195/667.htm
Modeling Resonant Structure in the Kuiper Belt
E.K. Holmes, S.F. Dermott, K. Grogan
http://www.aas.org/publications/baas/v31n5/aas195/474.htm
This meeting has numerous symposia covering primarily Earth geology, but of
particular interest to Kuiper belt studies are the Comparative Planetology
symposia, which are listed at:
http://www.31igc.org/first/scientif/general3.htm#25.
For information about symposium 25.2: ``Geoscientific Research of the Outer Planets and their Satellites'', contact Jeffrey S. Kargel (jkargel@flagmail.wr.usgs.gov) or Christophe Sotin (sotin@chimie.univ-nantes.fr).
For information about symposium 25.4: ``Meteorites, Asteroids, Comets, and Cosmic Dust'' contact Gerhard Schwehm (gschwehm@estec.esa.nl) or Celso de Barros Gomes (marciacm@usp.br).
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.