316 research outputs found
Candidate Members and Age Estimate of the Family of Kuiper Belt Object 2003 EL61
The collisional family of Kuiper belt object (KBO) 2003 EL61 opens the
possibility for many interesting new studies of processes important in the
formation and evolution of the outer solar system. As the first family in the
Kuiper belt, it can be studied using techniques developed for studying asteroid
families, although some modifications are necessary. Applying these modified
techniques allows for a dynamical study of the 2003 EL61 family. The velocity
required to change orbits is used to quantitatively identify objects near the
collision. A method for identifying family members that have potentially
diffused in resonances (like 2003 EL61) is also developed. Known family members
are among the very closest KBOs to the collision and two new likely family
members are identified: 2003 UZ117 and 1999 OY3. We also give tables of
candidate family members which require future observations to confirm
membership. We estimate that a minimum of ~1 GYr is needed for resonance
diffusion to produce the current position of 2003 EL61, implying that the
family is likely primordial. Future refinement of the age estimate is possible
once (many) more resonant objects are identified. The ancient nature of the
collision contrasts with the seemingly fresh surfaces of known family members,
suggesting that our understanding of outer solar system surfaces is incomplete.Comment: 22 pages, 5 figures, accepted to AJ, author's cv available at
http://www.gps.caltech.edu/~dari
The size, density, and formation of the Orcus-Vanth system in the Kuiper belt
The Kuiper belt object Orcus and its satellite Vanth form an unusual system
in the Kuiper belt. Orcus is amongst the largest objects known in the Kuiper
belt, but the relative size of Vanth is much larger than that of the tiny
satellites of the other large objects. From Hubble Space Telescope observations
we find that Orcus and Vanth have different visible colors and that Vanth does
not share the water ice absorption feature seen in the infrared spectrum of
Orcus. We also find that Vanth has a nearly face-on circular orbit with a
period of 9.5393 +-0.0001 days and semimajor axis of 8980+-20 km, implying a
system mass of 6.32+- 0.01 X 10^20 kg or 3.8% the mass of dwarf planet Eris.
From Spitzer Space Telescope observations we find that the thermal emission
is consistent with a single body with diameter 940+-70 km and a geometric
albedo of 0.28+-0.04. Assuming equal densities and albedos, this measurements
implies sizes of Orcus and Vanth of 900 and 280 km, respectively, and a mass
ratio of 33. Assuming a factor of 2 lower albedo for the non-icy Vanth,
however, implies sizes of 820 and 640 km and a mass ratio of 2. The measured
density depends on the assumed albedo ratio of the two objects but is
approximately 1.5+-0.3 g cm^-3$, midway between typical densities measured for
larger and for smaller objects. The orbit and mass ratio is consistent with
formation from a giant impact and subsequent outward tidal evolution and even
consistent with the system having now achieved a double synchronous state. The
system can equally well be explained, however, by initial eccentric capture,
Kozai cycling which increases the eccentricity and decreases the pericenter of
the orbit of Vanth, and subsequent tidal evolution inward.Comment: Submitted to A
Resolving the Sin(I) degeneracy in Low-Mass Multi-Planet Systems
Long-term orbital evolution of multi-planet systems under tidal dissipation
often converges to a stationary state, known as the tidal fixed point. The
fixed point is characterized by a lack of oscillations in the eccentricities
and apsidal alignment among the orbits. Quantitatively, the nature of the fixed
point is dictated by mutual interactions among the planets as well as
non-Keplerian effects. We show that if a roughly coplanar system hosts a hot,
sub-Saturn mass planet, and is tidally relaxed, separation of planet-planet
interactions and non-Keplerian effects in the equations of motion leads to a
direct determination of the true masses of the planets. Consequently, a
"snap-shot" observational determination of the orbital state resolves the
sin(I) degeneracy, and opens up a direct avenue towards identification of the
true lowest-mass exo-planets detected. We present an approximate, as well as a
general, mathematical framework for computation of the line of sight
inclination of secular systems, and apply our models illustratively to the 61
Vir system. We conclude by discussing the observability of planetary systems to
which our method is applicable and we set our analysis into a broader context
by presenting a current summary of the various possibilities for determining
the physical properties of planets from observations of their orbital states.Comment: 9 pages, 7 figures, 1 table, Accepted to the Astrophysical Journa
The effect of orbital evolution on the Haumea (2003 EL61) collisional family
The Haumea family is currently the only identified collisional family in the
Kuiper belt. We numerically simulate the long-term dynamical evolution of the
family to estimate a lower limit of the family's age and to assess how the
population of the family and its dynamical clustering are preserved over Gyr
timescales. We find that the family is not younger than 100 Myr, and its age is
at least 1 Gyr with 95% confidence. We find that for initial velocity
dispersions of 50-400 m/s, approximately 20-45% of the family members are lost
to close encounters with Neptune after 3.5 Gyr of orbital evolution. We apply
these loss rates to two proposed models for the formation of the Haumea family,
a graze-and-merge type collision between two similarly sized, differentiated
KBOs or the collisional disruption of a satellite orbiting Haumea. For the
graze-and-merge collision model, we calculate that >85% of the expected mass in
surviving family members within 150 m/s of the collision has been identified,
but that one to two times the mass of the known family members remains to be
identified at larger velocities. For the satellite-break-up model, we estimate
that the currently identified family members account for ~50% of the expected
mass of the family. Taking observational incompleteness into account, the
observed number of Haumea family members is consistent with either formation
scenario at the 1 sigma level, however both models predict more objects at
larger relative velocities (>150 m/s) than have been identified.Comment: 25 pages, accepted to Icaru
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