James V. Scotti

NEOWISE Observations of Near-Earth Objects: Preliminary Results

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 surveys 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 Pan-STARRS Moving Object Processing System

ABSTRACT.We describe the Pan-STARRS Moving Object Processing System (MOPS), a modern software package that produces automatic asteroid discoveries and identifications from catalogs of transient detections from next-generation astronomical survey telescopes. MOPS achieves >99.5%>99.5% efficiency in producing orbits from a synthetic but realistic population of asteroids whose measurements were simulated for a Pan-STARRS4-class telescope. Additionally, using a nonphysical grid population, we demonstrate that MOPS can detect populations of currently unknown objects such as interstellar asteroids. MOPS has been adapted successfully to the prototype Pan-STARRS1 telescope despite differences in expected false detection rates, fill-factor loss, and relatively sparse observing cadence compared to a hypothetical Pan-STARRS4 telescope and survey. MOPS remains highly efficient at detecting objects but drops to 80% efficiency at producing orbits. This loss is primarily due to configurable MOPS processing limits that a...

The Spacewatch Wide-Area Survey for Bright Centaurs and Trans-Neptunian Objects

We have conducted a large-area search for the brightest members of the trans-Neptunian and Centaur/scattered-disk asteroid populations by reprocessing archival scans from the Spacewatch 0.9 m telescope at Kitt Peak. Our survey encompasses 331 scans taken from 1995 September to 1999 September and has a raw sky coverage of 1483.8 deg2. We discovered five trans-Neptunians and five Centaur/scattered-disk objects using an automated motion detection code. In addition, we serendipitously found four trans-Neptunians and two Centaur/scattered-disk objects that had been previously discovered. This survey is unique in that it involves a method that has a reasonable chance to reacquire its lost objects. In this paper we develop techniques to aid our understanding of our software efficiency and survey procedures. We use this understanding to convolve our raw sky coverage with our measured detection efficiency and a model of our scan coverage to estimate what fraction of survey areas can be considered new. Our large sky coverage extends the cumulative luminosity function of the trans-Neptunians into a region previously constrained only by upper limits, and it allows a power-law fit to be attempted to the Centaur cumulative luminosity function. In objects per square degree brighter than R = 21.5, we find cumulative surface densities of Centaurs to be 0.017 ± 0.011, of trans-Neptunians to be 0.040 ± 0.018, and scattered-disk objects to be 0.007 ± 0.004. We extrapolate these values to estimate the number of each class in the ecliptic brighter than R = 21.5: 100 Centaurs, 400 trans-Neptunians, and 70 scattered-disk objects. Orbit analysis by the Minor Planet Center suggests that three of our five trans-Neptunians are resonators: 1998 VG44 is in the 3 : 2, 1995 SM55 appears to be in the 5 : 3, and 1998 SN165 appears to be in the 7 : 5 resonance.

WISE/NEOWISE OBSERVATIONS OF ACTIVE BODIES IN THE MAIN BELT

We report results based on mid-infrared photometry of five 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 2010 April 2-3, three months after its peak activity. Photometry of the coma at 12 and 22 μm combined with ground-based visible-wavelength measurements provides constraints on the dust particle mass distribution (PMD), dlog n/dlog m, yielding power-law slope values of α = –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 CO_2 and CO production are also provided for each AMBO and compared with revised production numbers for WISE observations of 103P/Hartley 2.

The Search for Distant Objects in the Solar System Using Spacewatch

We have completed a low-inclination ecliptic survey for distant and slow-moving bright objects in the outer solar system. This survey used data taken over 34 months by the University of Arizonas Spacewatch Project based at Steward Observatory, Kitt Peak. Spacewatch revisits the same sky area every three to seven nights in order to track cohorts of main-belt asteroids. This survey used a multiple-night detection scheme to extend our rate sensitivity to as low as 0.012 arcsec hr-1. When combined with our plate scale and flux sensitivity (V ≈ 21), this survey was sensitive to Mars-sized objects out to 300 AU and Jupiter-sized planets out to 1200 AU. The survey covered approximately 8000 deg2 of raw sky, mostly within 10° of the ecliptic but away from the Galactic center. An automated motion-detection program was modified for this multinight search and processed approximately 2 terabytes of imagery into motion candidates. This survey discovered 2003 MW12, currently the tenth largest classical Kuiper Belt object. In addition, several known large Kuiper Belt objects and Centaurs were detected, and the detections were used with a model of our observational biases to make population estimates as a check on our survey efficiency. We found no large objects at low inclinations despite having sufficient sensitivity in both flux and rate to see them out as far as 1200 AU. For low inclinations, we can rule out more than one to two Pluto-sized objects out to 100 AU and one to two Mars-sized objects to 200 AU.

Computer Aided Near Earth Object Detection

The Spacewatch program at the University of Arizona has pioneered automatic methods of detecting Near Earth Objects. Our software presently includes three modes of object detection : automatic motion identification; automatic streak identification; and visual streak identification. For automatic motion detection at sidereal drift rates, the 4σ detection threshold is near magnitude V = 20.9 for nearly stellar asteroid images. The automatic streak detection is able to locate streaks whose peak signal is above ~4σ and whose length is longer than about 10 pixels. Some visually detected streaks have had peak signals near ~lσ.

Identifying near-Earth object families

Abstract The study of asteroid families has provided tremendous insight into the forces that sculpted the main belt and continue to drive the collisional and dynamical evolution of asteroids. The identification of asteroid families within the NEO population could provide a similar boon to studies of their formation and interiors. In this study we examine the purported identification of NEO families by Drummond [Drummond, J.D., 2000. Icarus 146, 453–475] and conclude that it is unlikely that they are anything more than random fluctuations in the distribution of NEO osculating orbital elements. We arrive at this conclusion after examining the expected formation rate of NEO families, the identification of NEO groups in synthetic populations that contain no genetically related NEOs, the orbital evolution of the largest association identified by Drummond [Drummond, J.D., 2000. Icarus 146, 453–475], and the decoherence of synthetic NEO families intended to reproduce the observed members of the same association. These studies allowed us to identify a new criterion that can be used to select real NEO families for further study in future analyses, based on the ratio of the number of pairs and the size of strings to the number of objects in an identified association.

Use Of A Scanning Ccd To Discriminate Asteroid Images Moving In A Field Of Stars

We are using a charge-coupled device (CCD) in a scanning mode to find new asteroids and recover known asteroids and comet nuclei. Current scientific programs include recovery of asteroids and comet nuclei requested by the Minor Planet Center (MPC), discovery of new asteroids in the main belt and of unusual orbital types, and follow-up astrometry of selected new asteroids we discover. The routine six sigma limiting visual magnitude is 19.6 and slightly more than a square degree is scanned three times every 90 minutes of observing time during the fortnight centered on new moon. Semiautomatic software for detection of moving objects is in routine use; angular speeds as low as 11.0 arcseconds per hour have been distinguished from the effects of the Earths atmosphere on the field of view. A typical set of three 29-minute scans near the opposition point along the ecliptic typically nets at least 5 new main-belt asteroids down to magnitude 19.6, but we do not follow all of those. In 18 observing runs (months) we have recovered 43 asteroids, discovered and reported astrometric and photometric data on 59 new asteroids, consolidated 10 new asteroids with orbital elements, and reported photometry and positions of 22 comets. We outline our future scientific programs that will take advantage of the expected performance of a Tektronix TK2048M-011 thick, quiet, cosmetically clean, front-illuminated CCD with 2048 x 2048 pixels that we have ordered.

Spacewatch Astrometry and Photometry of Near-Earth Objects

The Spacewatch Project uses four telescopes of apertures 0.9-m, 1.8-m, 2.3-m, and 4-m on Kitt Peak mountain in Arizona for followup astrometry of priority NEOs. Objects as faint as V=23 on the MPC’s NEO Confirmation Page, targets of radar, potential impactors, targets of spacecraft observations or visits, and PHAs with future close approaches to Earth receive priority for astrometry.