67 research outputs found
Ridge Formation and De-Spinning of Iapetus via an Impact-Generated Satellite
We present a scenario for building the equatorial ridge and de-spinning
Iapetus through an impact-generated disk and satellite. This impact puts debris
into orbit, forming a ring inside the Roche limit and a satellite outside. This
satellite rapidly pushes the ring material down to the surface of Iapetus, and
then itself tidally evolves outward, thereby helping to de-spin Iapetus. This
scenario can de-spin Iapetus an order of magnitude faster than when tides due
to Saturn act alone, almost independently of its interior geophysical
evolution. Eventually, the satellite is stripped from its orbit by Saturn. The
range of satellite and impactor masses required is compatible with the
estimated impact history of Iapetus.Comment: 19 pages, 3 figures; Icarus, in pres
(47171) 1999 TC36, A Transneptunian Triple
We present new analysis of HST images of (47171) 1999 TC36 that confirm it as
a triple system. Fits to the point-spread function consistently show that the
apparent primary is itself composed of two similar-sized components. The two
central components, A1 and A2, can be consistently identified in each of nine
epochs spread over seven years of time. In each instance the component
separation, ranging from 0.023+/-0.002 to 0.031+/-0.003 arcsec, is roughly one
half of the Hubble Space Telescope's diffraction limit at 606 nm. The orbit of
the central pair has a semi-major axis of a~867 km with a period of P~1.9 days.
These orbital parameters yield a system mass that is consistent with Msys =
12.75+/-0.06 10^18 kg derived from the orbit of the more distant secondary,
component B. The diameters of the three components are dA1= 286(+45,-38) km,
dA2= 265(+41,-35 km and dB= 139(+22,-18) km. The relative sizes of these
components are more similar than in any other known multiple in the solar
system. Taken together, the diameters and system mass yield a bulk density of
p=542(+317,-211) kg m^-3. HST Photometry shows that component B is variable
with an amplitude of >=0.17+/-0.05 magnitudes. Components A1 and A2 do not show
variability larger than 0.08+/-0.03 magnitudes approximately consistent with
the orientation of the mutual orbit plane and tidally-distorted equilibrium
shapes. The system has high specific angular momentum of J/J'=0.93, comparable
to most of the known Transneptunian binaries.Comment: 16 pages, 8 figures, 6 tables. Accepted to Icaru
The Correlated Colors of Transneptunian Binaries
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.Comment: 28 pages, 4 figure, 4 tables. accepted to Icaru
Mutual Events in the Cold Classical Transneptunian Binary System Sila and Nunam
Hubble Space Telescope observations between 2001 and 2010 resolved the binary
components of the Cold Classical transneptunian object (79360) Sila-Nunam
(provisionally designated 1997 CS29). From these observations we have
determined the circular, retrograde mutual orbit of Nunam relative to Sila with
a period of 12.50995 \pm 0.00036 days and a semimajor axis of 2777 \pm 19 km. A
multi-year season of mutual events, in which the two near-equal brightness
bodies alternate in passing in front of one another as seen from Earth, is in
progress right now, and on 2011 Feb. 1 UT, one such event was observed from two
different telescopes. The mutual event season offers a rich opportunity to
learn much more about this barely-resolvable binary system, potentially
including component sizes, colors, shapes, and albedo patterns. The low
eccentricity of the orbit and a photometric lightcurve that appears to coincide
with the orbital period are consistent with a system that is tidally locked and
synchronized, like the Pluto-Charon system. The orbital period and semimajor
axis imply a system mass of (10.84 \pm 0.22) \times 10^18 kg, which can be
combined with a size estimate based on Spitzer and Herschel thermal infrared
observations to infer an average bulk density of 0.72 +0.37 -0.23 g cm^-3,
comparable to the very low bulk densities estimated for small transneptunian
binaries of other dynamical classes.Comment: In press in Icaru
Oligarchic growth of giant planets
Runaway growth ends when the largest protoplanets dominate the dynamics of
the planetesimal disk; the subsequent self-limiting accretion mode is referred
to as ``oligarchic growth.'' Here, we begin by expanding on the existing
analytic model of the oligarchic growth regime. From this, we derive global
estimates of the planet formation rate throughout a protoplanetary disk. We
find that a relatively high-mass protoplanetary disk ( 10
minimum-mass) is required to produce giant planet core-sized bodies ( 10
M) within the lifetime of the nebular gas (\la 10 million years).
However, an implausibly massive disk is needed to produce even an Earth mass at
the orbit of Uranus by 10 Myrs. Subsequent accretion without the dissipational
effect of gas is even slower and less efficient. In the limit of
non-interacting planetesimals, a reasonable-mass disk is unable to produce
bodies the size of the Solar System's two outer giant planets at their current
locations on {\it any} timescale; if collisional damping of planetesimal random
velocities is sufficiently effective, though, it may be possible for a
Uranus/Neptune to form in situ in less than the age of the Solar System. We
perform numerical simulations of oligarchic growth with gas, and find that
protoplanet growth rates agree reasonably well with the analytic model as long
as protoplanet masses are well below their estimated final masses. However,
accretion stalls earlier than predicted, so that the largest final protoplanet
masses are smaller than those given by the model. Thus the oligarchic growth
model, in the form developed here, appears to provide an upper limit for the
efficiency of giant planet formation.Comment: ScienceDirect already has the final published version here:
dx.doi.org/10.1016/S0019-1035(02)00043-
The Kuiper Belt and Other Debris Disks
We discuss the current knowledge of the Solar system, focusing on bodies in
the outer regions, on the information they provide concerning Solar system
formation, and on the possible relationships that may exist between our system
and the debris disks of other stars. Beyond the domains of the Terrestrial and
giant planets, the comets in the Kuiper belt and the Oort cloud preserve some
of our most pristine materials. The Kuiper belt, in particular, is a
collisional dust source and a scientific bridge to the dusty "debris disks"
observed around many nearby main-sequence stars. Study of the Solar system
provides a level of detail that we cannot discern in the distant disks while
observations of the disks may help to set the Solar system in proper context.Comment: 50 pages, 25 Figures. To appear in conference proceedings book
"Astrophysics in the Next Decade
The Science of Sungrazers, Sunskirters, and Other Near-Sun Comets
This review addresses our current understanding of comets that venture close to the Sun, and are hence exposed to much more extreme conditions than comets that are typically studied from Earth. The extreme solar heating and plasma environments that these objects encounter change many aspects of their behaviour, thus yielding valuable information on both the comets themselves that complements other data we have on primitive solar system bodies, as well as on the near-solar environment which they traverse. We propose clear definitions for these comets: We use the term near-Sun comets to encompass all objects that pass sunward of the perihelion distance of planet Mercury (0.307 AU). Sunskirters are defined as objects that pass within 33 solar radii of the Sun’s centre, equal to half of Mercury’s perihelion distance, and the commonly-used phrase sungrazers to be objects that reach perihelion within 3.45 solar radii, i.e. the fluid Roche limit. Finally, comets with orbits that intersect the solar photosphere are termed sundivers. We summarize past studies of these objects, as well as the instruments and facilities used to study them, including space-based platforms that have led to a recent revolution in the quantity and quality of relevant observations. Relevant comet populations are described, including the Kreutz, Marsden, Kracht, and Meyer groups, near-Sun asteroids, and a brief discussion of their origins. The importance of light curves and the clues they provide on cometary composition are emphasized, together with what information has been gleaned about nucleus parameters, including the sizes and masses of objects and their families, and their tensile strengths. The physical processes occurring at these objects are considered in some detail, including the disruption of nuclei, sublimation, and ionisation, and we consider the mass, momentum, and energy loss of comets in the corona and those that venture to lower altitudes. The different components of comae and tails are described, including dust, neutral and ionised gases, their chemical reactions, and their contributions to the near-Sun environment. Comet-solar wind interactions are discussed, including the use of comets as probes of solar wind and coronal conditions in their vicinities. We address the relevance of work on comets near the Sun to similar objects orbiting other stars, and conclude with a discussion of future directions for the field and the planned ground- and space-based facilities that will allow us to address those science topics
Origin and Evolution of Saturn's Ring System
The origin and long-term evolution of Saturn's rings is still an unsolved
problem in modern planetary science. In this chapter we review the current
state of our knowledge on this long-standing question for the main rings (A,
Cassini Division, B, C), the F Ring, and the diffuse rings (E and G). During
the Voyager era, models of evolutionary processes affecting the rings on long
time scales (erosion, viscous spreading, accretion, ballistic transport, etc.)
had suggested that Saturn's rings are not older than 100 My. In addition,
Saturn's large system of diffuse rings has been thought to be the result of
material loss from one or more of Saturn's satellites. In the Cassini era, high
spatial and spectral resolution data have allowed progress to be made on some
of these questions. Discoveries such as the ''propellers'' in the A ring, the
shape of ring-embedded moonlets, the clumps in the F Ring, and Enceladus' plume
provide new constraints on evolutionary processes in Saturn's rings. At the
same time, advances in numerical simulations over the last 20 years have opened
the way to realistic models of the rings's fine scale structure, and progress
in our understanding of the formation of the Solar System provides a
better-defined historical context in which to understand ring formation. All
these elements have important implications for the origin and long-term
evolution of Saturn's rings. They strengthen the idea that Saturn's rings are
very dynamical and rapidly evolving, while new arguments suggest that the rings
could be older than previously believed, provided that they are regularly
renewed. Key evolutionary processes, timescales and possible scenarios for the
rings's origin are reviewed in the light of tComment: Chapter 17 of the book ''Saturn After Cassini-Huygens'' Saturn from
Cassini-Huygens, Dougherty, M.K.; Esposito, L.W.; Krimigis, S.M. (Ed.) (2009)
537-57
Investigating the DART Impact Event with the Lucy LOng Range Reconnaissance Imager
NASA’s Lucy mission is the first to provide flyby reconnaissance of the Jovian trojan asteroids, which are thought to be primordial small bodies that formed at a variety of heliocentric distances during the early stages of the solar system’s formation and were subsequently captured into Jupiter’s L4 and L5 Lagrange stability zones. Since its successful launch on 2021-Oct-16, the Lucy spacecraft has been orbiting the sun within the inner solar system. On 2022-Oct-16, Lucy executes the first of three Earth Gravity Assists (EGAs) that put the spacecraft on the correct trajectory to achieve its encounters with the Jovian trojans. The DART kinetic impact on the secondary body of the Didymos-Dimorphos binarysystem occurs 20 days prior to EGA1, at a time when the Lucy spacecraft is well-placed to observe it. Lucy carries a sensitive panchromatic camera, the Lucy LOng Range Reconnaissance Imager (L’LORRI), which is capable of detecting the binary system with high signal-to-noise ratio (SNR) and with temporal cadences as fast as once per second.
The observing geometry from Lucy is similar to that from the Earth: the range to the Didymos system is 0.126 au from Lucy vs 0.0757 au from Earth, and the solar phase angle is 31.9 deg vs 53.2 deg. The L’LORRI investigation of the DART impact event is divided into eight separate observational phases, starting 12 hr before the impact and ending 24 hr afterwards. L’LORRI cannot resolve the binary, but instead records the total brightness, which is expected to increase after the DART impact due to reflected sunlight from the ejecta. The first two phases are designed to obtain baseline photometry of the Didymos system covering both the Didymos-Dimorphos mutual orbit period (11.92 hr) and the rotational period of Didymos (2.26 hr). Phase 3 covers the impact event itself at one second cadence, starting 3 minutes beforeimpact and ending 4 minutes afterwards. Lucy has a clear view of the predicted DART impact site, theoretically enablingL’LORRI to detect an optical flash in the unlikely event it is brighter than Didymos itself. L’LORRI observations during phases 4 through 8 are designed to monitor the temporal and spatial evolution of ejecta associated with the impact event, but ejecta don’t leave the central pixel during Lucy’s observing period unless their speed is greater than about 2 m/s
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