488 research outputs found
Asteroid occultations today and tomorrow: toward the GAIA era
Context: Observation of star occultations is a powerful tool to determine
shapes and sizes of asteroids. This is key information necessary for studying
the evolution of the asteroid belt and to calibrate indirect methods of size
determination, such as the models used to analyze thermal infrared
observations. Up to now, the observation of asteroid occultations is an
activity essentially secured by amateur astronomers equipped with small,
portable equipments. However, the accuracy of the available ephemeris prevents
accurate predictions of the occultation events for objects smaller than ~100
km. Aims: We investigate current limits in predictability and observability of
asteroid occultations, and we study their possible evolution in the future,
when high accuracy asteroid orbits and star positions (such as those expected
from the mission Gaia of the European Space Agency) will be available. Methods:
We use a simple model for asteroid ephemeris uncertainties and numerical
algorithms for estimating the limits imposed by the instruments, assuming
realistic CCD performances and asteroid size distribution, to estimate the
expected occultation rate under different conditions. Results: We show that
high accuracy ephemerides which will be available in the future will extend
toward much smaller asteroids the possibility of observing asteroid
occultations, greatly increasing the number of events and objects involved. A
complete set of size measurements down to ~10 km main belt asteroids could be
obtained in a few years, provided that a small network of ground-based 1m
telescopes are devoted to occultation studies
Asteroid Models from Multiple Data Sources
In the past decade, hundreds of asteroid shape models have been derived using
the lightcurve inversion method. At the same time, a new framework of 3-D shape
modeling based on the combined analysis of widely different data sources such
as optical lightcurves, disk-resolved images, stellar occultation timings,
mid-infrared thermal radiometry, optical interferometry, and radar
delay-Doppler data, has been developed. This multi-data approach allows the
determination of most of the physical and surface properties of asteroids in a
single, coherent inversion, with spectacular results. We review the main
results of asteroid lightcurve inversion and also recent advances in multi-data
modeling. We show that models based on remote sensing data were confirmed by
spacecraft encounters with asteroids, and we discuss how the multiplication of
highly detailed 3-D models will help to refine our general knowledge of the
asteroid population. The physical and surface properties of asteroids, i.e.,
their spin, 3-D shape, density, thermal inertia, surface roughness, are among
the least known of all asteroid properties. Apart for the albedo and diameter,
we have access to the whole picture for only a few hundreds of asteroids. These
quantities are nevertheless very important to understand as they affect the
non-gravitational Yarkovsky effect responsible for meteorite delivery to Earth,
or the bulk composition and internal structure of asteroids.Comment: chapter that will appear in a Space Science Series book Asteroids I
Heating of near-Earth objects and meteoroids due to close approaches to the Sun
It is known that near-Earth objects (NEOs) during their orbital evolution may
often undergo close approaches to the Sun. Indeed it is estimated that up to
~70% of them end their orbital evolution colliding with the Sun. Starting from
the present orbital properties, it is possible to compute the most likely past
evolution for every NEO, and to trace its distance from the Sun. We find that a
large fraction of the population may have experienced in the past frequent
close approaches, and thus, as a consequence, a considerable Sun-driven
heating, not trivially correlated to the present orbits. The detailed dynamical
behaviour, the rotational and the thermal properties of NEOs determine the
exact amount of the resulting heating due to the Sun. In the present paper we
discuss the general features of the process, providing estimates of the surface
temperature reached by NEOs during their evolution. Moreover, we investigate
the effects of this process on meteor-size bodies, analyzing possible
differences with the NEO population. We also discuss some possible effects of
the heating which can be observed through remote sensing by ground-based
surveys or space missions.Comment: 8 pages, 5 figures, accepted by MNRA
Thermophysical properties of near-Earth asteroid (341843) 2008 EV5 from WISE data
Aims. To derive the thermal inertia of 2008 EV, the baseline target for
the Marco Polo-R mission proposal, and infer information about the size of the
particles on its surface. Methods. Values of thermal inertia are obtained by
fitting an asteroid thermophysical model to NASA's Wide-field Infrared Survey
Explorer (WISE) infrared data. From the constrained thermal inertia and a model
of heat conductivity that accounts for different values of the packing fraction
(a measure of the degree of compaction of the regolith particles), grain size
is derived. Results. We obtain an effective diameter , geometric visible albedo (assuming
), and thermal inertia J/m2/s(1/2)/K at
the 1- level of significance for its retrograde spin pole solution. The
regolith particles radius is mm for low degrees of
compaction, and mm for the highest packing densities.Comment: 16 pages, 8 figures; accepted for publication in Astronomy &
Astrophysic
The effect of rotation and tidal heating on the thermal lightcurves of Super Mercuries
Short period (<50 days) low-mass (<10Mearth) exoplanets are abundant and the
few of them whose radius and mass have been measured already reveal a diversity
in composition. Some of these exoplanets are found on eccentric orbits and are
subjected to strong tides affecting their rotation and resulting in significant
tidal heating. Within this population, some planets are likely to be depleted
in volatiles and have no atmosphere. We model the thermal emission of these
"Super Mercuries" to study the signatures of rotation and tidal dissipation on
their infrared light curve. We compute the time-dependent temperature map at
the surface and in the subsurface of the planet and the resulting
disk-integrated emission spectrum received by a distant observer for any
observation geometry. We calculate the illumination of the planetary surface
for any Keplerian orbit and rotation. We include the internal tidal heat flow,
vertical heat diffusion in the subsurface and generate synthetic light curves.
We show that the different rotation periods predicted by tidal models
(spin-orbit resonances, pseudo-synchronization) produce different photometric
signatures, which are observable provided that the thermal inertia of the
surface is high, like that of solid or melted rocks (but not regolith). Tidal
dissipation can also directly affect the light curves and make the inference of
the rotation more difficult or easier depending on the existence of hot spots
on the surface. Infrared light curve measurement with the James Webb Space
Telescope and EChO can be used to infer exoplanets' rotation periods and
dissipation rates and thus to test tidal models. This data will also constrain
the nature of the (sub)surface by constraining the thermal inertia.Comment: 15 pages, 13 figures, accepted for publication in Astronomy &
Astrophysic
ExploreNEOs VIII: Dormant Short-Period Comets in the Near-Earth Asteroid Population
We perform a search for dormant comets, asteroidal objects of cometary
origin, in the near-Earth asteroid (NEA) population based on dynamical and
physical considerations. Our study is based on albedos derived within the
ExploreNEOs program and is extended by adding data from NEOWISE and the Akari
asteroid catalog. We use a statistical approach to identify asteroids on orbits
that resemble those of short-period near-Earth comets using the Tisserand
parameter with respect to Jupiter, the aphelion distance, and the minimum
orbital intersection distance with respect to Jupiter. From the sample of NEAs
on comet-like orbits, we select those with a geometric albedo
as dormant comet candidates, and find that only 50% of NEAs on comet-like
orbits also have comet-like albedos. We identify a total of 23 NEAs from our
sample that are likely to be dormant short-period near-Earth comets and, based
on a de-biasing procedure applied to the cryogenic NEOWISE survey, estimate
both magnitude-limited and size-limited fractions of the NEA population that
are dormant short-period comets. We find that 0.3-3.3% of the NEA population
with , and % of the population with diameters km, are dormant short-period near-Earth comets.Comment: 23 pages, 2 figures, 2 tables; accepted for publication in A
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