Recent radar observations of asteroid 1566 Icarus

The Near-Earth Asteroid Size–Frequency Distribution: A Snapshot of the Lunar Impactor Size–Frequency Distribution

“…Since small NEAs are probably mostly fragments from collisions in the main belt, they may exhibit fresher, less space-weathered, and therefore more reflective surfaces than larger, older asteroids. There is some evidence for higher visual geometric albedos among small NEAs from thermalinfrared and radar observations (see, for example, Harris et al 1998, Harris and Davies 1999, Mahapatra et al 1999. While it is possible that such results are entirely due to observation selection effects and/or modeling uncertainties, it is nevertheless interesting to note that if p v = 0.25 is used to convert the projectile SFD to an H -value frequency distribution (corresponding to a diameter of 1 km for H = 17.1) the dashed curve shown in Fig.…”

Asteroid 1566 Icarus’s Size, Shape, Orbit, and Yarkovsky Drift from Radar Observations

“…The most highly red-and blue-shifted signals are reflected from these high-incidence regions, and the large attenuation of these signals reduces the span of the measured bandwidth. This effect may also explain a discrepancy noticed by Mahapatra et al (1999), who measured Icarus' bandwidth during its previous radar apparition nearly two decades ago, and pointed out that the measured bandwidth corresponds to a diameter around half of the value found radiometrically by Harris (1998).…”

“…We can determine which of these two possibilities is more likely by analyzing historical radar measurements of this object. Table 9 lists Icarus' reported bandwidths from the three radar apparitions that garnered CW measurements -namely 1968 Goldstein 1969), 1996(Mahapatra et al 1999, and 2015 (this work) -along with the bandwidths that would have been measured at the corresponding dates, if Icarus' spin pole orientation were constant. We generated predictions for four possible spin poles -λ = 313…”

“…In modern times, the radar apparitions occurred in 1968, 1996, and 2015. Following the 1996 radar observations, Mahapatra et al (1999) described Doppler spectra but did not report a detection in delay-Doppler images. Here, we report results from the 2015 Arecibo and Goldstone observations.…”

Yarkovsky Effect on Small Near-Earth Asteroids: Mathematical Formulation and Examples

“…This albedo, however, seems to be quite large, and Harris (1998) advocated a larger size for this asteroid and a correspondingly smaller optical albedo. In a recent paper, Mahapatra et al (1999) however seem to indicate that the original solution of small-size Icarus might be correct. (This issue is carefully considered in Section 3.3.…”