-
A. Mainzer,
T. Grav,
J. Bauer,
J. Masiero,
R. S. McMillan,
R. M. Cutri,
R. Walker,
E. Wright,
P. Eisenhardt,
D. J. Tholen, [......],
J. A. Larsen,
C. Maleszewski,
M. A. Malkan,
J.-C. Mauduit,
B. L. Mullan,
E. W. Olszewski,
J. Pforr,
A. Saro,
J. V. Scotti,
and L. H. Wasserman
[show abstract]
[hide abstract]
ABSTRACT: With the NEOWISE portion of the Wide-field Infrared Survey Explorer (WISE) project, we have carried out a highly uniform survey of the near-Earth object (NEO) population at thermal infrared wavelengths ranging from 3 to 22 μm, allowing us to refine estimates of their numbers, sizes, and albedos. The NEOWISE survey detected NEOs the same way whether they were previously known or not, subject to the availability of ground-based follow-up observations, resulting in the discovery of more than 130 new NEOs. The survey's uniform sensitivity, observing cadence, and image quality have permitted extrapolation of the 428 near-Earth asteroids (NEAs) detected by NEOWISE during the fully cryogenic portion of the WISE mission to the larger population. We find that there are 981 ± 19 NEAs larger than 1 km and 20,500 ± 3000 NEAs larger than 100 m. We show that the Spaceguard goal of detecting 90% of all 1 km NEAs has been met, and that the cumulative size distribution is best represented by a broken power law with a slope of 1.32 ± 0.14 below 1.5 km. This power-law slope produces ~13, 200 ± 1900 NEAs with D > 140 m. Although previous studies predict another break in the cumulative size distribution below D ~ 50-100 m, resulting in an increase in the number of NEOs in this size range and smaller, we did not detect enough objects to comment on this increase. The overall number for the NEA population between 100 and 1000 m is lower than previous estimates. The numbers of near-Earth comets and potentially hazardous NEOs will be the subject of future work.
The Astrophysical Journal 12/2011; 743(2):156. · 6.02 Impact Factor
-
A. Mainzer,
J. Masiero,
T. Grav,
J Bauer,
D. J. Tholen,
R. S. Mcmillan,
E Wright,
T. Spahr,
R. M. Cutri,
R Walker, W. Mo,
J. Watkins,
E. Hand,
C. Maleszewski
[show abstract]
[hide abstract]
ABSTRACT: We have combined the NEOWISE and Sloan Digital Sky Survey data to study the
albedos of 24,353 asteroids with candidate taxonomic classifications derived
using Sloan photometry. We find a wide range of moderate to high albedos for
candidate S-type asteroids that are analogous to the S-complex defined by
previous spectrophotometrically-based taxonomic systems. The candidate C-type
asteroids, while generally very dark, have a tail of higher albedos that
overlaps the S types. The albedo distribution for asteroids with a
photometrically derived Q classification is extremely similar to those of the S
types. Asteroids with similar colors to (4) Vesta have higher albedos than the
S types, and most have orbital elements similar to known Vesta family members.
Finally, we show that the relative reflectance at 3.4 and 4.6 $\mu$m is higher
for D-type asteroids and suggest that their red visible and near-infrared
spectral slope extends out to these wavelengths. Understanding the relationship
between size, albedo, and taxonomic classification is complicated by the fact
that the objects with classifications were selected from the
visible/near-infrared Sloan Moving Object Catalog, which is biased against
fainter asteroids, including those with lower albedos.
The Astrophysical Journal 10/2011; 745(1). · 6.02 Impact Factor
-
A. Mainzer,
T. Grav,
J. Masiero,
J Bauer,
E. Hand,
D. Tholen,
R. S. Mcmillan,
T. Spahr,
R. M. Cutri,
E Wright,
J. Watkins, W. Mo,
C. Maleszewski
[show abstract]
[hide abstract]
ABSTRACT: The NEOWISE dataset offers the opportunity to study the variations in albedo
for asteroid classification schemes based on visible and near-infrared
observations for a large sample of minor planets. We have determined the
albedos for nearly 1900 asteroids classified by the Tholen, Bus and Bus-DeMeo
taxonomic classification schemes. We find that the S-complex spans a broad
range of bright albedos, partially overlapping the low albedo C-complex at
small sizes. As expected, the X-complex covers a wide range of albedos. The
multi-wavelength infrared coverage provided by NEOWISE allows determination of
the reflectivity at 3.4 and 4.6 $\mu$m relative to the visible albedo. The
direct computation of the reflectivity at 3.4 and 4.6 $\mu$m enables a new
means of comparing the various taxonomic classes. Although C, B, D and T
asteroids all have similarly low visible albedos, the D and T types can be
distinguished from the C and B types by examining their relative reflectance at
3.4 and 4.6 $\mu$m. All of the albedo distributions are strongly affected by
selection biases against small, low albedo objects, as all objects selected for
taxonomic classification were chosen according to their visible light
brightness. Due to these strong selection biases, we are unable to determine
whether or not there are correlations between size, albedo and space
weathering. We argue that the current set of classified asteroids makes any
such correlations difficult to verify. A sample of taxonomically classified
asteroids drawn without significant albedo bias is needed in order to perform
such an analysis.
The Astrophysical Journal 09/2011; 741(2). · 6.02 Impact Factor
-
A. Mainzer,
T. Grav,
J Bauer,
J. Masiero,
R. S. Mcmillan,
R. M. Cutri,
R Walker,
E Wright,
P. Eisenhardt,
D. J. Tholen, [......],
J. A. Larsen,
C. Maleszewski,
M. A. Malkan,
J. -C. Mauduit,
B. L. Mullan,
E. W. Olszewski,
J. Pforr,
A. Saro,
J. V. Scotti,
L. H. Wasserman
[show abstract]
[hide abstract]
ABSTRACT: With the NEOWISE portion of the \emph{Wide-field Infrared Survey Explorer}
(WISE) project, we have carried out a highly uniform survey of the near-Earth
object (NEO) population at thermal infrared wavelengths ranging from 3 to 22
$\mu$m, allowing us to refine estimates of their numbers, sizes, and albedos.
The NEOWISE survey detected NEOs the same way whether they were previously
known or not, subject to the availability of ground-based follow-up
observations, resulting in the discovery of more than 130 new NEOs. The
survey's uniformity in sensitivity, observing cadence, and image quality have
permitted extrapolation of the 428 near-Earth asteroids (NEAs) detected by
NEOWISE during the fully cryogenic portion of the WISE mission to the larger
population. We find that there are 981$\pm$19 NEAs larger than 1 km and
20,500$\pm$3000 NEAs larger than 100 m. We show that the Spaceguard goal of
detecting 90% of all 1 km NEAs has been met, and that the cumulative size
distribution is best represented by a broken power law with a slope of
1.32$\pm$0.14 below 1.5 km. This power law slope produces $\sim13,200\pm$1,900
NEAs with $D>$140 m. Although previous studies predict another break in the
cumulative size distribution below $D\sim$50-100 m, resulting in an increase in
the number of NEOs in this size range and smaller, we did not detect enough
objects to comment on this increase. The overall number for the NEA population
between 100-1000 m are lower than previous estimates. The numbers of near-Earth
comets will be the subject of future work.
09/2011;
