6,463 research outputs found
Aharonov-Bohm Problem for Spin-One
The basic AB problem is to determine how an unshielded tube of magnetic flux
affects arbitrarily long-wavelength charged particles impinging on it.
For spin-1 at almost all the particles do not penetrate the tube, so the
interaction essentially is periodic in (AB effect). Below-threshold
bound states move freely only along the tube axis, and consequent induced
vacuum currents supplement rather than screen . For a pure magnetic
interaction the tube must be broader than the particle Compton wavelength,
i.e., only the nonrelativistic spin-1 AB problem exists.Comment: 15 pages, Late
Planetary Trojans - the main source of short period comets?
We present a short review of the impact regime experienced by the terrestrial
planets within our own Solar system, describing the three populations of
potentially hazardous objects which move on orbits that take them through the
inner Solar system. Of these populations, the origins of two (the Near-Earth
Asteroids and the Long-Period Comets) are well understood, with members
originating in the Asteroid belt and Oort cloud, respectively. By contrast, the
source of the third population, the Short-Period Comets, is still under debate.
The proximate source of these objects is the Centaurs, a population of
dynamically unstable objects that pass perihelion between the orbits of Jupiter
and Neptune. However, a variety of different origins have been suggested for
the Centaur population. Here, we present evidence that at least a significant
fraction of the Centaur population can be sourced from the planetary Trojan
clouds, stable reservoirs of objects moving in 1:1 mean-motion resonance with
the giant planets (primarily Jupiter and Neptune). Focusing on simulations of
the Neptunian Trojan population, we show that an ongoing flux of objects should
be leaving that region to move on orbits within the Centaur population. With
conservative estimates of the flux from the Neptunian Trojan clouds, we show
that their contribution to that population could be of order ~3%, while more
realistic estimates suggest that the Neptune Trojans could even be the main
source of fresh Centaurs. We suggest that further observational work is needed
to constrain the contribution made by the Neptune Trojans to the ongoing flux
of material to the inner Solar system, and believe that future studies of the
habitability of exoplanetary systems should take care not to neglect the
contribution of resonant objects (such as planetary Trojans) to the impact flux
that could be experienced by potentially habitable worlds.Comment: 16 pages, 4 figures, published in the International Journal of
Astrobiology (the arXiv.org's abstract was shortened, but the original one
can be found in the manuscript file
(1173) Anchises - Thermophysical and Dynamical Studies of a Dynamically Unstable Jovian Trojan
We have performed detailed thermophysical and dynamical modelling of Jovian
Trojan (1173) Anchises. Our results reveal a most unusual object. By examining
observational data taken by IRAS, Akari and WISE between 11.5 and 60 microns,
along with variations in its optical lightcurve, we find Anchises is most
likely an elongated body, with an axes-ratio of ~1.4. This yields calculated
best-fit dimensions of 170x121x121km (an equivalent diameter of 136+18/-11km).
We find the observations are best fit by Anchises having a retrograde sense of
rotation, and an unusually high thermal inertia (25 to 100 Jm-2s-0.5K-1). The
geometric albedo is found to be 0.027 (+0.006/-0.007). Anchises therefore has
one of the highest published thermal inertias of any object larger than 100km
in diameter, at such large heliocentric distances, and is one of the lowest
albedo objects ever observed. More observations are needed to see if there is a
link between the very shallow phase curve, with almost no opposition effect,
and the derived thermal properties for this large Trojan asteroid. Our
dynamical investigation of Anchises' orbit has revealed it to be dynamically
unstable on timescales of hundreds of Myr, similar to the unstable Neptunian
Trojans 2001 QR322 and 2008 LC18. Unlike those objects, we find that Anchises'
dynamical stability is not a function of its initial orbital elements, the
result of the exceptional precision with which its orbit is known. This is the
first time that a Jovian Trojan has been shown to be dynamically unstable, and
adds weight to the idea that planetary Trojans represent a significant ongoing
contribution to the Centaur population, the parents of the short-period comets.
The observed instability does not rule out a primordial origin for Anchises,
but when taken in concert with the result of our thermophysical analysis,
suggest that it would be a fascinating target for future study.Comment: 5 figures, 3 tables, accepted for publication in Monthly Notices of
the Royal Astronomical Societ
Origin and Dynamical Evolution of Neptune Trojans - II: Long Term Evolution
We present results examining the fate of the Trojan clouds produced in our
previous work. We find that the stability of Neptunian Trojans seems to be
strongly correlated to their initial post-migration orbital elements, with
those objects that survive as Trojans for billions of years displaying
negligible orbital evolution. The great majority of these survivors began the
integrations with small eccentricities (e < 0.2) and small libration amplitudes
(A < 30 - 40{\deg}). The survival rate of "pre-formed" Neptunian Trojans (which
in general survived on dynamically cold orbits (e < 0.1, i < 5 - 10{\deg}))
varied between ~5 and 70%. By contrast, the survival rate of "captured" Trojans
(on final orbits spread across a larger region of e-i element space) were
markedly lower, ranging between 1 and 10% after 4 Gyr. Taken in concert with
our earlier work, we note that planetary formation scenarios which involve the
slow migration (a few tens of millions of years) of Neptune from an initial
planetary architecture that is both resonant and compact (aN < 18 AU) provide
the most promising fit of those we considered to the observed Trojan
population. In such scenarios, we find that the current day Trojan population
would number ~1% of that which was present at the end of the planet's
migration, with the bulk being sourced from captured, rather than pre-formed
objects. We note, however, that even those scenarios still fail to reproduce
the currently observed portion of the Neptune Trojan population moving on
orbits with e 20{\deg}. Dynamical integrations of the currently
observed Trojans show that five out of the seven are dynamically stable on 4
Gyr timescales, while 2001 QR322, exhibits significant dynamical instability.
The seventh Trojan object, 2008 LC18, has such large orbital uncertainties that
only future studies will be able to determine its stability.Comment: 24 pages, 6 figures, accepted for publication in MNRAS (The abstract
was shortened. Original version can be found in the pdf file
Formation and Dynamical Evolution of the Neptune Trojans - the Influence of the Initial Solar System Architecture
In this work, we investigate the dynamical stability of pre-formed Neptune
Trojans under the gravitational influence of the four giant planets in compact
planetary architectures, over 10 Myr. In our modelling, the initial orbital
locations of Uranus and Neptune (aN) were varied to produce systems in which
those planets moved on non-resonant orbits, or in which they lay in their
mutual 1:2, 2:3 and 3:4 mean-motion resonances (MMRs). In total, 420
simulations were carried out, examining 42 different architectures, with a
total of 840000 particles across all runs. In the non-resonant cases, the
Trojans suffered only moderate levels of dynamical erosion, with the most
compact systems (those with aN less than or equal 18 AU) losing around 50% of
their Trojans by the end of the integrations. In the 2:3 and 3:4 MMR scenarios,
however, dynamical erosion was much higher with depletion rates typically
greater than 66% and total depletion in the most compact systems. The 1:2
resonant scenarios featured disruption on levels intermediate between the
non-resonant cases and other resonant scenarios, with depletion rates of the
order of tens of percent. Overall, the great majority of plausible
pre-migration planetary architectures resulted in severe levels of depletion of
the Neptunian Trojan clouds. In particular, if Uranus and Neptune formed near
their mutual 2:3 or 3:4 MMR and at heliocentric distances within 18 AU (as
favoured by recent studies), we found that the great majority of pre-formed
Trojans would have been lost prior to Neptune's migration. This strengthens the
case for the great bulk of the current Neptunian Trojan population having been
captured during that migration.Comment: 17 pages, 2 figures, MNRAS (in press). Abstract slightly reduced in
size, but in original form in the PDF fil
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