MAIN BELT ASTEROIDS WITHWISE/NEOWISE. I. PRELIMINARY ALBEDOS AND DIAMETERS

Abstract

We present initial results from the Wide-field Infrared Survey Explorer (WISE), a four-band all-sky thermal infrared survey that produces data well suited to measuring the physical properties of asteroids, and the NEOWISE enhancement to the WISE mission allowing for detailed study of Solar system objects. Using a NEATM thermal model fitting routine we compute diameters for over 100,000 Main Belt asteroids from their IR thermal flux, with errors better than 10%. We then incorporate literature values of visible measurements (in the form of the H absolute magnitude) to determine albedos. Using these data we investigate the albedo and diameter distributions of the Main Belt. As observed previously, we find a change in the average albedo when comparing the inner, middle, and outer portions of the Main Belt. We also confirm that the albedo distribution of each region is strongly bimodal. We observe groupings of objects with similar albedos in regions of the Main Belt associated with dynamical breakup families. Asteroid families typically show a characteristic albedo for all members, but there are notable exceptions to this. This paper is the first look at the Main Belt asteroids in the WISE data, and only represents the preliminary, observed raw size and albedo distributions for the populations considered. These distributions are subject to survey biases inherent to the NEOWISE dataset and cannot yet be interpreted as describing the true populations; the debiased size and albedo distributions will be the subject of the next paper in this series.

Basalt or Not? Near-infrared Spectra, Surface Mineralogical Estimates, and Meteorite Analogs for 33 Vp-type Asteroids

“…Compositional suggestions from an asteroid taxonomy can only be made broadly and must be done with caution (Tholen 1984). Our sample of V p asteroids also have NEOWISE-derived albedos that are broadly consistent with (4) Vesta (Tedesco et al 2002;Masiero et al 2011;Mainzer et al 2016); together these provide the best indirect evidence of a likely basaltic nature for this taxonomic group of asteroids.…”

“…These two groups of V p asteroids are called innerbelt and outer-belt basaltic asteroid candidates, respectively. All the asteroids in Table 1 have NEOWISE-derived effective diameters (D eff )<11 km (Masiero et al 2011;Mainzer et al 2016) with a mean effective diameter of 4.872 km. Our target asteroids were also selected based on NEOWISE-derived geometric albedos (p v ) that are generally consistent with (4) Vesta (p v =0.4228, Tedesco et al 2002), but span a range in p v from 0.178 to 0.554 with a mean value of 0.343.…”

Characterizing the original ejection velocity field of the Koronis family

“…If we assume that errors on the standard deviations in proper e and sin(i) are proportional to (n)/n, with n the number of objects in each size bin, then that would correspond to rejecting samples with a error larger than ≃ 20%. By using this approach we are consistent with the method of other authors ( (Masiero et al, 2011)), that also did not considered populations of asteroids with D > 12 km to avoid smallnumber statistics issues. For the sake of brevity, we will define the 6 < D < 10, 4 < D < 6, and 2 < D < 4 km size bins as D 8 , D 5 , and D 3 populations, respectively.…”

Space weathering trends among carbonaceous asteroids

“…Although the slope evolution of C-complex asteroids appears consistent with silicate-rich asteroids (Nesvorný et al 2005;Lazzarin et al 2006), the albedo trends are not. Masiero et al (2011) find the younger Karin family has a lower albedo than the older Koronis family. In contrast, our data suggest the younger Beagle asteroids have a higher albedo than the older Themis asteroids.…”