113 research outputs found
Shape-Driven Selection Effects for Aspherical Near-Earth Objects in Systematic Surveys
The apparent magnitude of elongated small bodies is time-dependent over their
rotation phase. Therefore, previously undiscovered aspherical minor planets may
experience a shape-driven selection effect in systematic surveys versus their
spherical counterparts. In this study, we conduct injection-recovery exercises
of synthetic asteroid lightcurves using a simple model to quantify the effect
of varying axial ratio on detection efficiencies. We find that high-amplitude
lightcurves are confronted with adverse selection effects for survey cadences
and discovery thresholds for constructing tracklets that are representative of
modern and proposed future NEO searches. Furthermore, we illustrate the
possible hazards of drawing population-level inferences on an underlying
reservoir of elongated small bodies. If physical size and characteristic axial
ratios are correlated, then size-frequency distributions may require revision
at small diameters. In particular, this effect could alter the estimated
populations of near-Earth objects. We conclude by discussing the applicability
of our results to various other classes of solar system minor planets and
interstellar interlopers, as well as discuss future work that may further
interrogate this detection bias.Comment: 21 pages, 10 figure, 1 table. Accepted for publication in Icarus.
(small typo fixed in v2
Minimum fuel round trip from a Earth-Moon Halo orbit to Asteroid 2006 RH
International audienceThe goal of this paper is to design a spacecraft round trip transfer from a parking orbit to Asteroid 2006\;RH, during its capture time by Earth's gravity, while maximizing the final mass or equivalently minimizing the delta-v. The parking orbit is chosen as a Halo orbit around the Earth-Moon libration point. The round-trip transfer is composed of three portions: a rendezvous transfer departing from the parking orbit to reach 2006\;RH, a lock-in portion with the spacecraft following the asteroid orbit, and finally a return transfer to . An indirect method based on the maximum principle is used for our numerical calculations. To partially address the issue of local minima, we restrict the control strategy to reflect an actuation corresponding to up to three constant thrust arcs during each portion of the transfer. The model considered here is the circular restricted four-body problem (CR4BP) with the Sun considered as a perturbation of the Earth-Moon circular restricted three body problem. A shooting method is applied to solve numerically this problem, and the rendezvous point to and departure point from \RH\ are optimized using a time discretization of the trajectory of \RH
The Size-Frequency Distribution of Dormant Jupiter Family Comets
We estimate the total number and the slope of the size frequency distribution
(SFD) of dormant Jupiter Family Comets (JFCs) by fitting a one-parameter model
to the known population. We first select 61 Near Earth Objects (NEOs) that are
likely to be dormant JFCs because their orbits are dynamically coupled to
Jupiter (Bottke et al, 2002). Then, from the numerical simulations of Levison &
Duncan (1997), we construct an orbit distribution model for JFCs in the NEO
orbital element space. We assume an orbit independent SFD for all JFCs, the
slope of which is our unique free parameter. Finally, we compute observational
biases for dormant JFCs using a calibrated NEO survey simulator (Jedicke et al.
2003). By fitting the biased model to the data, we estimate that there are ~75
dormant JFCs with H<18 in the NEO region and that the slope of their cumulative
SFD is -1.5 +/- 0.3. Our slope for the SFD of dormant JFCs is very close to
that of active JFCs as determined by Weissman and Lowry (2003). Thus, we argue
that when JFCs fade they are likely to become dormant rather than to disrupt
and that the fate of faded comets is size independent. Our results imply that
the size distribution of the JFC progenitors - the scattered disk
trans-Neptunian population - either (i) has a similar and shallow SFD or (i')
is slightly steeper and physical processes acting on the comets in a
size-dependent manner creates the shallower active comet SFD. Our measured
slope, typical of collisionally evolved populations with a size dependent
impact strength (Benz and Asphaug 1999), suggests that scattered disk bodies
reached collisional equilibrium inside the proto-planetary disk prior to their
removal from the planetary region.Comment: 33 pages, 6 figure
The population of natural Earth satellites
Peer reviewe
Surveys, Astrometric Follow-up & Population Statistics
Asteroid surveys are the backbone of asteroid science, and with this in mind
we begin with a broad review of the impact of asteroid surveys on our field. We
then provide a brief history of asteroid discoveries so as to place
contemporary and future surveys in perspective. Surveys in the United States
have discovered the vast majority of the asteroids and this dominance has been
consolidated since the publication of Asteroids III. Our descriptions of the
asteroid surveys that have been operational since that time are focussed upon
those that have contributed the vast majority of asteroid observations and
discoveries. We also provide some insight into upcoming next-generation surveys
that are sure to alter our understanding of the small bodies in the inner solar
system and provide evidence to untangle their complicated dynamical and
physical histories. The Minor Planet Center, the nerve center of the asteroid
discovery effort, has improved its operations significantly in the past decade
so that it can manage the increasing discovery rate, and ensure that it is
well-placed to handle the data rates expected in the next decade. We also
consider the difficulties associated with astrometric follow-up of newly
identified objects. It seems clear that both of these efforts must operate in
new modes in order to keep pace with expected discovery rates of
next-generation ground- and space-based surveys.Comment: Chapter to appear in the book ASTEROIDS IV, (University of Arizona
Press) Space Science Series, edited by P. Michel, F. DeMeo and W. Bottk
The Thousand Asteroid Light Curve Survey
We present the results of our Thousand Asteroid Light Curve Survey (TALCS)
conducted with the Canada-France-Hawaii Telescope in September 2006. Our
untargeted survey detected 828 Main Belt asteroids to a limiting magnitude of
g'~22.5 corresponding to a diameter range of 0.4 km <= D <= 10 km. Of these,
278 objects had photometry of sufficient quality to perform rotation period
fits. We debiased the observations and light curve fitting process to determine
the true distribution of rotation periods and light curve amplitudes of Main
Belt asteroids. We confirm a previously reported excess in the fraction of fast
rotators but find a much larger excess of slow rotating asteroids (~15% of our
sample). A few percent of objects in the TALCS size range have large light
curve amplitudes of ~1 mag. Fits to the debiased distribution of light curve
amplitudes indicate that the distribution of triaxial ellipsoid asteroid shapes
is proportional to the square of the axis-ratio, (b/a)^2, and may be bi-modal.
Finally, we find six objects with rotation periods that may be less than 2
hours with diameters between 400 m and 1.5 km, well above the break-up limit
for a gravitationally-bound aggregate. Our debiased data indicate that this
population represents <4% of the Main Belt in the 1-10 km size range.Comment: Accepted to Icarus. Full tables to appear there in electronic format,
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