41 research outputs found
The NEO Surveyor Near Earth Asteroid Known Object Model
The known near-Earth object (NEO) population consists of over 32,000 objects,
with a yearly discovery rate of over 3000 NEOs per year. An essential component
of the next generation of NEO surveys is an understanding of the population of
known objects, including an accounting of the discovery rate per year as a
function of size. Using a near-Earth asteroid (NEA) reference model developed
for NASA's NEO Surveyor (NEOS) mission and a model of the major current and
historical ground-based surveys, an estimate of the current NEA survey
completeness as a function of size and absolute magnitude has been determined
(termed the Known Object Model; KOM). This allows for understanding of the
intersection of the known catalog of NEAs and the objects expected to be
observed by NEOS. The current NEA population is found to be complete
for objects larger than 140m, consistent with estimates by Harris & Chodas
(2021). NEOS is expected to catalog more than two thirds of the NEAs larger
than 140m, resulting in of NEAs cataloged at the end of its 5 year
nominal survey (Mainzer et al, 2023}, making significant progress towards the
US Congressional mandate. The KOM estimates that of the currently
cataloged objects will be detected by NEOS, with those not detected
contributing to the final completeness at the end its 5 year mission.
This model allows for placing the NEO Surveyor mission in the context of
current surveys to more completely assess the progress toward the goal of
cataloging the population of hazardous asteroids.Comment: 27 pages, 18 figures, 3 tables. Accepted for publication in Planetary
Science Journal (PSJ
WISE/NEOWISE Preliminary Analysis and Highlights of the 67P/Churyumov-Gerasimenko Near Nucleus Environs
On January 18-19 and June 28-29 of 2010, the Wide-field Infrared Survey
Explorer (WISE) spacecraft imaged the Rosetta mission target, comet
67P/Churyumov-Gerasimenko. We present a preliminary analysis of the images,
which provide a characterization of the dust environment at heliocentric
distances similar to those planned for the initial spacecraft encounter, but on
the outbound leg of its orbit rather than the inbound. Broad-band photometry
yields low levels of CO2 production at a comet heliocentric distance of 3.32 AU
and no detectable production at 4.18 AU. We find that at these heliocentric
distances, large dust grains with mean grain diameters on the order of a
millimeter or greater dominate the coma and evolve to populate the tail. This
is further supported by broad-band photometry centered on the nucleus, which
yield an estimated differential dust particle size distribution with a power
law relation that is considerably shallower than average. We set a 3-sigma
upper limit constraint on the albedo of the large-grain dust at <= 0.12. Our
best estimate of the nucleus radius (1.82 +/- 0.20 km) and albedo (0.04 +/-
0.01) are in agreement with measurements previously reported in the literature
Size and Albedo Constraints for (152830) Dinkinesh Using WISE Data
Probing small main-belt asteroids provides insight into their formation and
evolution through multiple dynamical and collisional processes. These asteroids
also overlap in size with the potentially hazardous near-earth object
population and supply the majority of these objects. The Lucy mission will
provide an opportunity for study of a small main-belt asteroid, (152830)
Dinkinesh. The spacecraft will perform a flyby of this object on November 1,
2023, in preparation for its mission to the Jupiter Trojan asteroids. We
employed aperture photometry on stacked frames of Dinkinesh obtained by the
Wide-field-Infrared Survey Explorer and performed thermal modeling on a
detection at 12 m to compute diameter and albedo values. Through this
method, we determined Dinkinesh has an effective spherical diameter of
km and a visual geometric albedo of
at the 16th and 84th percentiles. This albedo is
consistent with typical stony (S-type) asteroids.Comment: Submitted to Astrophysical Journal Letter
WISE/NEOWISE Observations of Comet 103P/Hartley 2
We report results based on mid-infrared photometry of comet 103P/Hartley 2 taken during 2010 May 4-13 (when the comet was at a heliocentric distance of 2.3 AU, and an observer distance of 2.0 AU) by the Wide-field Infrared Survey Explorer. Photometry of the coma at 22 μm and data from the University of Hawaii 2.2 m telescope obtained on 2010 May 22 provide constraints on the dust particle size distribution, d log n/d log m, yielding power-law slope values of alpha = –0.97 ± 0.10, steeper than that found for the inbound particle fluence during the Stardust encounter of comet 81P/Wild 2. The extracted nucleus signal at 12 μm is consistent with a body of average spherical radius of 0.6 ± 0.2 km (one standard deviation), assuming a beaming parameter of 1.2. The 4.6 μm band signal in excess of dust and nucleus reflected and thermal contributions may be attributed to carbon monoxide or carbon dioxide emission lines and provides limits and estimates of species production. Derived carbon dioxide coma production rates are 3.5(± 0.9) × 10^(24) molecules per second. Analyses of the trail signal present in the stacked image with an effective exposure time of 158.4 s yields optical-depth values near 9 × 10^(–10) at a delta mean anomaly of 0.2 deg trailing the comet nucleus, in both 12 and 22 μm bands. A minimum chi-squared analysis of the dust trail position yields a beta-parameter value of 1.0 × 10^(–4), consistent with a derived mean trail-grain diameter of 1.1/ρ cm for grains of ρ g cm^(–3) density. This leads to a total detected trail mass of at least 4 × 10^(10) ρ kg
The NEOWISE-Discovered Comet Population and the CO+CO_2 production rates
The 163 comets observed during the WISE/NEOWISE prime mission represent the largest infrared survey to date of comets, providing constraints on dust, nucleus size, and CO + CO_2 production. We present detailed analyses of the WISE/NEOWISE comet discoveries, and discuss observations of the active comets showing 4.6 μm band excess. We find a possible relation between dust and CO + CO_2 production, as well as possible differences in the sizes of long and short period comet nuclei
WISE/NEOWISE observations of Active Bodies in the Main Belt
We report results based on mid-infrared photometry of 5 active main belt
objects (AMBOs) detected by the Wide-field Infrared Survey Explorer (WISE)
spacecraft. Four of these bodies, P/2010 R2 (La Sagra), 133P/Elst-Pizarro,
(596) Scheila, and 176P/LINEAR, showed no signs of activity at the time of the
observations, allowing the WISE detections to place firm constraints on their
diameters and albedos. Geometric albedos were in the range of a few percent,
and on the order of other measured comet nuclei. P/2010 A2 was observed on
April 2-3, 2010, three months after its peak activity. Photometry of the coma
at 12 and 22 {\mu}m combined with ground-based visible-wavelength measurements
provides constraints on the dust particle mass distribution (PMD), dlogn/dlogm,
yielding power-law slope values of {\alpha} = -0.5 +/- 0.1. This PMD is
considerably more shallow than that found for other comets, in particular
inbound particle fluence during the Stardust encounter of comet 81P/Wild 2. It
is similar to the PMD seen for 9P/Tempel 1 in the immediate aftermath of the
Deep Impact experiment. Upper limits for CO2 & CO production are also provided
for each AMBO and compared with revised production numbers for WISE
observations of 103P/Hartley 2.Comment: 32 Pages, including 5 Figure
Centaurs and Scattered Disk Objects in the Thermal Infrared: Analysis of WISE/NEOWISE Observations
The Wide-field Infrared Survey Explorer (WISE) observed 52 Centaurs and scattered disk objects (SDOs) in the thermal infrared, including 15 new discoveries. We present analyses of these observations to estimate sizes and mean optical albedos. We find mean albedos of 0.08 ± 0.04 for the entire data set. Thermal fits yield average beaming parameters of 0.9 ± 0.2 that are similar for both SDO and Centaur sub-classes. Biased cumulative size distributions yield size-frequency distribution power law indices of ~–1.7 ± 0.3. The data also reveal a relation between albedo and color at the 3σ level. No significant relation between diameter and albedos is found
The Near-Earth Object Surveyor Mission
The Near-Earth Object (NEO) Surveyor mission is a NASA observatory designed
to discover and characterize near-Earth asteroids and comets. The mission's
primary objective is to find the majority of objects large enough to cause
severe regional impact damage (140 m in effective spherical diameter) within
its five-year baseline survey. Operating at the Sun-Earth L1 Lagrange point,
the mission will survey to within 45 degrees of the Sun in an effort to find
the objects in the most Earth-like orbits. The survey cadence is optimized to
provide observational arcs long enough to reliably distinguish near-Earth
objects from more distant small bodies that cannot pose an impact hazard. Over
the course of its survey, NEO Surveyor will discover 200,000 - 300,000
new NEOs down to sizes as small as 10 m and thousands of comets,
significantly improving our understanding of the probability of an Earth impact
over the next century.Comment: accepted to PS