39 research outputs found
Oort Cloud Comets Discovered Far from the Sun
Context: Increasingly, Oort Cloud comets are being discovered at great
distances from the Sun and tracked over ever wider ranges of heliocentric
distances as observational equipment improves. Aims: To investigate in detail
how the original semimajor axis for near-parabolic comets depends on the
selected data arc and the assumed form of the non-gravitational (NG)
acceleration. Methods: Among currently known Oort Cloud comets with large
perihelion distances ( au), we selected 32 objects observed over the
widest ranges of heliocentric distances in orbital legs before and after
perihelion. For each of them, we determined a series of orbits using at least
three basic types of data sets selected from available positional data (pre-
and post-perihelion data and the entire data set), and a few forms of NG
acceleration representing water ice or CO sublimation. Results: We found that
the motion of comets is often measurably affected by NG forces at heliocentric
distances beyond 5 au from the Sun. The most spectacular example is C/2010 U3
(Boattini), whose perihelion distance is 8.44 au. NG effects are detectable for
19 of the 32 comets within the positional data. For five comets, we found
asymmetric effects of NG forces - in three cases significantly greater before
perihelion than afterward (C/2017 M4, C/2000 SV, and C/2015 O1), and in
two others the opposite (C/1997 BA and C/2006 S3). We also find that the
well-known systematic effect of finding more tightly bound original orbits when
including the NG acceleration than in purely gravitational solutions may be
related to the specific form of the standard function describing the
sublimation of ices.Comment: 22 pages, 11 tables, 10 figures. Astronomy & Astrophysics, in pres
Planetary ring studies
The following topics are covered: (1) characterization of the fine scale structure in Saturn's A and B rings; (2) ballistic transport modeling and evolution of fine ring structure; (3) faint features in the rings of Saturn; (4) the Encke moonlet; (5) dynamics in ringmoon systems; (6) a nonclassical radiative transfer model; and (7) particle properties from stellar occultation data
Considerations on the magnitude distributions of the Kuiper belt and of the Jupiter Trojans
By examining the absolute magnitude (H) distributions (hereafter HD) of the
cold and hot populations in the Kuiper belt and of the Trojans of Jupiter, we
find evidence that the Trojans have been captured from the outer part of the
primordial trans-Neptunian planetesimal disk. We develop a sketch model of the
HDs in the inner and outer parts of the disk that is consistent with the
observed distributions and with the dynamical evolution scenario known as the
`Nice model'. This leads us to predict that the HD of hot population should
have the same slope of the HD of the cold population for 6.5 < H < 9, both as
steep as the slope of the Trojans' HD. Current data partially support this
prediction, but future observations are needed to clarify this issue. Because
the HD of the Trojans rolls over at H~9 to a collisional equilibrium slope that
should have been acquired when the Trojans were still embedded in the
primordial trans-Neptunian disk, our model implies that the same roll-over
should characterize the HDs of the Kuiper belt populations, in agreement with
the results of Bernstein et al. (2004) and Fuentes and Holman (2008). Finally,
we show that the constraint on the total mass of the primordial trans-Neptunian
disk imposed by the Nice model implies that it is unlikely that the cold
population formed beyond 35 AU.Comment: Icarus (2009) in pres
Impact Rates in the Outer Solar System
Previous studies of cometary impacts in the outer Solar System used the
spatial distribution of ecliptic comets (ECs) from dynamical models that
assumed ECs began on low-inclination orbits (<5 deg) in the Kuiper belt. In
reality, the source population of ECs - the trans-Neptunian scattered disk -
has orbital inclinations reaching up to ~30 deg. In Nesvorny et al. (2017), we
developed a new dynamical model of ECs by following comets as they evolved from
the scattered disk to the inner Solar System. The model was absolutely
calibrated from the population of Centaurs and active ECs. Here we use our EC
model to determine the steady-state impact flux of cometary/Centaur impactors
on Jupiter, Saturn, Uranus, and their moons. Relative to previous work (Zahnle
et al. 2003), we find slightly higher impact probabilities on the outer moons
and lower impact probabilities on the inner moons. The impact probabilities are
smaller when comet disruption is accounted for. The results provide a modern
framework for the interpretation of the cratering record in the outer Solar
System.Comment: PSJ, in pres
Phase light curves for extrasolar Jupiters and Saturns
We predict how a remote observer would see the brightness variations of giant
planets similar to Jupiter and Saturn as they orbit their central stars. We
model the geometry of Jupiter, Saturn and Saturn's rings for varying orbital
and viewing parameters. Scattering properties for the planets and rings at
wavelenghts 0.6-0.7 microns follow Pioneer and Voyager observations, namely,
planets are forward scattering and rings are backward scattering. Images of the
planet with or without rings are simulated and used to calculate the
disk-averaged luminosity varying along the orbit, that is, a light curve is
generated. We find that the different scattering properties of Jupiter and
Saturn (without rings) make a substantial difference in the shape of their
light curves. Saturn-size rings increase the apparent luminosity of the planet
by a factor of 2-3 for a wide range of geometries. Rings produce asymmetric
light curves that are distinct from the light curve of the planet without
rings. If radial velocity data are available for the planet, the effect of the
ring on the light curve can be distinguished from effects due to orbital
eccentricity. Non-ringed planets on eccentric orbits produce light curves with
maxima shifted relative to the position of the maximum planet's phase. Given
radial velocity data, the amount of the shift restricts the planet's unknown
orbital inclination and therefore its mass. Combination of radial velocity data
and a light curve for a non-ringed planet on an eccentric orbit can also be
used to constrain the surface scattering properties of the planet. To summarize
our results for the detectability of exoplanets in reflected light, we present
a chart of light curve amplitudes of non-ringed planets for different
eccentricities, inclinations, and the viewing azimuthal angles of the observer.Comment: 40 pages, 13 figures, submitted to Ap.
Reflected Light Curves, Spherical and Bond Albedos of Jupiter- and Saturn-like Exoplanets
Reflected light curves observed for exoplanets indicate that a few of them host bright clouds. We estimate how the light curve and total stellar heating of a planet depends on forward and backward scattering in the clouds based on Pioneer and Cassini spacecraft images of Jupiter and Saturn. We fit analytical functions to the local reflected brightnesses of Jupiter and Saturn depending on the planet's phase. These observations cover broadbands at 0.59–0.72 and 0.39–0.5 μm, and narrowbands at 0.938 (atmospheric window), 0.889 (CH4 absorption band), and 0.24–0.28 μm. We simulate the images of the planets with a ray-tracing model, and disk-integrate them to produce the full-orbit light curves. For Jupiter, we also fit the modeled light curves to the observed full-disk brightness. We derive spherical albedos for Jupiter and Saturn, and for planets with Lambertian and Rayleigh-scattering atmospheres. Jupiter-like atmospheres can produce light curves that are a factor of two fainter at half-phase than the Lambertian planet, given the same geometric albedo at transit. The spherical albedo is typically lower than for a Lambertian planet by up to a factor of ~1.5. The Lambertian assumption will underestimate the absorption of the stellar light and the equilibrium temperature of the planetary atmosphere. We also compare our light curves with the light curves of solid bodies: the moons Enceladus and Callisto. Their strong backscattering peak within a few degrees of opposition (secondary eclipse) can lead to an even stronger underestimate of the stellar heating
The Collisional Evolution of the Primordial Kuiper Belt, Its Destabilized Population, and the Trojan Asteroids
The tumultuous early era of outer solar system evolution culminated when
Neptune migrated across the primordial Kuiper belt (PKB) and triggered a
dynamical instability among the giant planets. This event led to the ejection
of approximately 99.9\% of the PKB (here called the destabilized population),
heavy bombardment of the giant planet satellites, and the capture of Jupiter's
Trojans. While this scenario has been widely tested using dynamical models,
there have been fewer investigations into how the PKB, its destabilized
population, and the Trojans experienced collisional evolution. Here we examined
this issue for all three populations with the code Boulder. Our constraints
included the size-frequency distributions (SFDs) of the Trojan asteroids and
craters on the giant planet satellites. Using this combination, we solved for
the unknown disruption law affecting bodies in these populations. The weakest
ones, from an impact energy per mass perspective, were 20 m in diameter.
Overall, collisional evolution produces a power-law-like shape for
multikilometer Trojans and a wavy-shaped SFD in the PKB and destabilized
populations. The latter can explain (i) the shapes of the ancient and younger
crater SFDs observed on the giant planet satellites, (ii) the shapes of the
Jupiter family and long-period comet SFDs, which experienced different degrees
of collision evolution, and (iii) the present-day impact frequency of
superbolides on Jupiter and smaller projectiles on Saturn's rings. Our model
results also indicate that many observed comets, most which are smaller than 10
km in diameter, are likely to be gravitational aggregates formed by large-scale
collision events.Comment: 95 pages, 19 figures. Accepted for publication in PS