Measuring the Abundance of Sub-Kilometer-Sized Kuiper Belt Objects Using Stellar Occultations

Abstract

We present here the analysis of about 19,500 new star hours of low ecliptic latitude observations (|b| ≤ 20 • ) obtained by the Hubble Space Telescope's Fine Guidance Sensors over a time span of more than nine years; which is an addition to the ∼ 12, 000 star hours previously analyzed by Schlichting et al. (2009). Our search for stellar occultations by small Kuiper belt objects (KBOs) yielded one new candidate event corresponding to a body with a 530 ± 70m radius at a distance of about 40 AU. Using bootstrap simulations, we estimate a probability of ≈ 5%, that this event is due to random statistical fluctuations within the new data set. Combining this new event with the single KBO occultation reported by Schlichting et al. (2009) we arrive at the following results: 1) The ecliptic latitudes of 6.6 • and 14.4 • of the two events are consistent with the observed inclination distribution of larger, 100 km-sized KBOs. 2) Assuming that small, sub-km sized KBOs have the same ecliptic latitude distribution as their larger counterparts, we find an ecliptic surface density of KBOs with radii larger than 250 m of N(r > 250 m) = 1.1 +1.5 −0.7 × 10 7 deg −2 ; if sub-km sized KBOs have instead a uniform ecliptic latitude distribution for −20 • < b < 20 • then N(r > 250 m) = 4.4 +5.8 −2.8 ×10 6 deg −2 . This is the best measurement of the surface density of sub-km sized KBOs to date. 3) Assuming the KBO size distribution can be well described by a single power law given by N(> r) ∝ r 1−q , where N(> r) is the number of KBOs with radii greater than r, and q is the power law index, we find q = 3.8±0.2 and q = 3.6±0.2 for a KBO ecliptic latitude distribution that follows the observed distribution for larger, 100-km sized KBOs and a uniform KBO ecliptic latitude distribution for −20 • < b < 20 • , respectively. 4) Regardless of the exact power law, our results suggest that small KBOs are numerous enough to satisfy the required supply rate for the Jupiter family comets. 5) We can rule out a single power law below the break with q > 4.0 at 2σ, confirming a strong deficit of sub-km sized KBOs compared to a population extrapolated from objects with r > 45 km. This suggests that small KBOs are undergoing collisional erosion and that the Kuiper belt is a true analogue to the dust producing debris disks observed around other stars.

On the Mass and Origin of Chariklo’s Rings

“…From Schlichting et al (2012), the optical depth to collisions for a ∼150 km target is ∼´-4.6 10 5 km projectile size…”

Pipeline for the Detection of Serendipitous Stellar Occultations by Kuiper Belt Objects with the Colibri Fast-photometry Array

“…A follow-up survey of 19,500 additional star hours yielded a second occultation candidate (Schlichting et al, 2012).…”

Upper limits to the number of Oort Cloud objects based on serendipitous occultation events search in X-rays

“…Optical search has the advantage of monitoring many stars at the same time, while in X-rays even smaller objects can be probed because of less diffraction in the occultation light curve. To date, such search is focused on pinning down the size distribution of small KBOs (Roques et al 2006;Bickerton, Kavelaars & Welch 2008;Schlichting et al 2012;Chang, Liu & Chen 2013;Zhang et al 2013;Liu et al 2015), which are located mainly between 30 and 50 AU. We now extend this effort to the Oort Cloud, using X-ray data.…”

“…It does not help to have a smaller Fresnel scale by observing at shorter optical wavelength. Some detections have been reported with fewer data of high signal-to-noise ratio obtained by space missions like HST (Schlichting et al 2012) and CoRoT (Liu et al 2015). These high-quality data make possible the detection of occultation events caused by KBOs of about 500-m size, roughly half a Fresnel scale.…”

“…Their existence, however, in addition to being inferred from observations of long-period comets, may also be explored by occultation events that they cause to distant background stars. Such an approach, looking for serendipitous occultation events from a vast amount c 2016 RAS of data, has been being employed to study the size distribution of small Kuiper Belt Objects (KBOs) down to sub-kilometer size using optical data (Roques et al 2006;Bickerton, Kavelaars & Welch 2008;Schlichting et al 2012;Zhang et al 2013;Liu et al 2015) and even to decameter size using X-ray observations (Chang, Liu & Chen 2013). It has also been applied to estimating upper limits to the number of small objects at distances between 100 and 1000 AU with data accumulated by the TAOS project (Wang et al 2009).…”