95 research outputs found
Origin of the Near-Ecliptic Circumsolar Dust Band
The zodiacal dust bands are bright infrared (IR) strips produced by thermal emission from circumsolar rings of particles. Two of the three principal dust bands, known as β and γ, were previously linked to the recent asteroid collisions that produced groups of fragments, so-called asteroid families, near the orbits of (832) Karin and (490) Veritas. The origin of the third, near-ecliptic α band has been unknown until now. Here we report the discovery of a recent breakup of a >20 km diameter asteroid near α's originally suspected source location in the Themis family. Numerical modeling and observations of the α-band thermal emission from the Spitzer Space Telescope indicate that the discovered breakup is the source of α-band particles. The recent formation of all principal dust bands implies a significant time variability of the circumstellar debris disks
Distribution of spin-axes longitudes and shape elongations of main-belt asteroids
Context: Large all-sky surveys provide us with a lot of photometric data that
are sparse in time (typically few measurements per night) and can be
potentially used for the determination of shapes and rotational states of
asteroids. The method which is generally used to derive these parameters is the
lightcurve inversion. However, for most asteroids their sparse data are not
accurate enough to derive a unique model and the lightcurve inversion method is
thus not very efficient.
Aims: To fully utilize photometry sparse in time, we developed a new
simplified model and applied it on the data from the Lowell photometric
database. Our aim was to derive spin axis orientations and shape elongations of
asteroids and to reconstruct distributions of these parameters for selected
subpopulations to find if there are some differences.
Methods: We model asteroids as geometrically scattering triaxial ellipsoids.
Observed values of mean brightness and the dispersion of brightness are
compared with computed values obtained from the parameters of the model --
ecliptical longitude and latitude of the pole and the ratios
, of axes of the ellipsoid. These parameters are optimized to get
the best agreement with the observation.
Results: We found that the distribution of for main-belt asteroids
is not uniform (in agreement with findings of Bowell et al., 2014, M&PS, 49,
95) and is dependent on the inclination of orbit. Surprisingly, the
non-uniformity of distribution is larger for asteroids residing on
low-inclination orbits. We also studied distributions of for several
groups of asteroids and found that small asteroids (km) are on average
more elongated than large ones.Comment: 10 pages; Accepted for publication in A&
Observations of "Fresh" and Weathered Surfaces on Asteroid Pairs and Their Implications on the Rotational-Fission Mechanism
The rotational-fission of a rubble-pile asteroid can result in an "asteroid
pair", two un-bound asteroids sharing similar orbits. This mechanism might
exposes material that previously had never have been exposed to the weathering
conditions of space. Therefore, the surfaces of asteroid pairs offer the
opportunity to observe non-weathered fresh spectra. We report near-IR
spectroscopic observations of 31 asteroids in pairs. We analyze their spectral
slopes, 1 {\mu}m absorption band, taxonomy, and estimate the time elapsed since
their separation. Analyzing the 19 S-complex objects in our sample, we find two
fresh Q-type asteroids that are the first of their kind to be observed in the
main-belt over the full visible and near-IR range. This solidly demonstrates
that Q-type objects are not limited to the NEA population. The pairs in our
sample present a range of fresh and weathered surfaces with no clear evidence
for a correlation with the ages of the pairs. However, our sample includes old
pairs (1 to 2 My) that present low spectral slopes. This illustrates a
timescale of at least ~2 My before an object develops high spectral slope that
is typical for S-type asteroids.
We discuss mechanisms that explain the existence of weathered pairs with
young dynamical ages and find that the "secondary fission" model (Jacobson &
Scheeres 2011) is the most robust with our observations since: 1) the secondary
members in our sample present fresh parameters that tend to be fresher than
their weathered primaries; 2) most of the fresh pairs in our sample have low
size ratios between the secondary and the primary; 3) 33% of the primaries in
our sample are fresh, similar to the prediction set by this model; 4) known
satellites orbit two of the pairs in our sample with low size ratio and fresh
surface; 5) there is no correlation between the weathering state and the
primary shape as predicted by other models.Comment: 19 pages, 17 figures, 4 tables. Accepted to Icaru
Origin and Evolution of Jupiter's Trojan Asteroids
The origin of the Jupiter Trojan asteroids has long been a mystery.
Dynamically, the population, which is considerably smaller than the main
asteroid belt, librates around Jupiter's stable L4 and L5 Lagrange points, 60
deg ahead and behind Jupiter. It is thought that these bodies were captured
into these orbits early in solar system history, but any capture mechanism must
also explain why the Trojans have an excited inclination distribution, with
some objects reaching inclinations of 35 deg. The Trojans themselves,
individually and in aggregate, also have spectral and physical properties that
appear consistent with many small bodies found in the outer solar system (e.g.,
irregular satellites, Kuiper belt objects). In this review, we assemble what is
known about the Trojans and discuss various models for their origin and
collisional evolution. It can be argued that the Trojans are unlikely to be
captured planetesimals from the giant planet zone, but instead were once
denizens of the primordial Kuiper belt, trapped by the events taking place
during a giant planet instability. The Lucy mission to the Trojans is therefore
well positioned to not only answer questions about these objects, but also
about their place in planet formation and solar system evolution studies.Comment: 30 pages, 4 figure
Short-lived Delocalization and Absorption by Light
Coherent exciton delocalization improves the light harvesting function of photosyn- thetic antennae by creating conditions for very fast excitation transfer in space. This thesis focuses on two different effects creating coherence - short-lived excitation by light and weak coupling between pigments that is present in the system on longer timescales. The evolution and relaxation of simple systems - the dimer and trimer - are calculated. The core of this thesis are newly developed numerical methods for distinguishing and quantifying the effect of the two types of coherence throughout evolution, which are applied to the aforementioned systems. 1Koherentní delokalizace excitonů zlepšuje funkci sběru světla fotosyntetických antén tím, že vytváří podmínky pro velmi rychlý přenos excitace v prostoru. Tato práce se zaměřuje na dva různé efekty vytvářející koherenci - krátkodobé excitace světlem a sla- bou vazbu mezi pigmenty, které jsou v systému přítomny v delším časovém měřítku. Je vypočten vývoj a relaxace jednoduchých systémů - dimeru a trimeru. Hlavní část práce prezentuje nové numerické metody pro rozlišení dvou typů koherence v průběhu evoluce, a jejich aplikaci na zmíněné systémy. 1Institute of Physics of Charles UniversityFyzikální ústav UKMatematicko-fyzikální fakultaFaculty of Mathematics and Physic
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