A single sub-kilometre Kuiper belt object from a stellar occultation in archival data

Abstract

The Kuiper belt is a remnant of the primordial Solar System. Measurements of its size distribution constrain its accretion and collisional history, and the importance of material strength of Kuiper belt objects (KBOs)(1; 2; 3; 4). Small, sub-km sized, KBOs elude direct detection, but the signature of their occultations of background stars should be detectable (5; 6; 7; 8; 9). Observations at both optical(10) and Xray(11) wavelengths claim to have detected such occultations, but their implied KBO abundances are inconsistent with each other and far exceed theoretical expectations. Here, we report an analysis of archival data that reveals an occultation by a body with a ∼500 m radius at a distance of 45 AU. The probability of this event to occur due to random statistical fluctuations within our data set is about 2%. Our survey yields a surface density of KBOs with radii larger than 250 m of 2.1 +4.8 −1.7 × 10 7 deg −2 , ruling out inferred surface densities from previous claimed detections by more than 5 σ. The fact that we detected only one event, firmly shows a deficit of sub-km sized KBOs compared to a population extrapolated from objects with r > 50 km. This implies that sub-km-sized KBOs are undergoing collisional erosion, just like debris disks observed around other stars.A small KBO crossing the line of sight to a star will partially obscure the stellar light, an event which can be detected in the star's light curve. For visible light, the characteristic scale of diffraction effects, known as the Fresnel scale, is given by (λa/2) 1/2 ∼ 1.3 km, where a ∼ 40 AU is the distance to the Kuiper belt and λ ∼ 600 nm is the wavelength of our observations. Diffraction effects will be apparent in the star's light curve due to occulting KBOs provided that both star and the occulting object are smaller than the Fresnel scale (12; 13). Occultations by objects smaller than the Fresnel scale are in the Fraunhofer regime. In this regime the diffraction pattern is determined by the size of the KBO and its distance -2 -to the observer, the angular size of the star, the wavelength range of the observations and the impact parameter between the star and the KBO (see Supplementary Information for details). The duration of the occultation is approximately given by the ratio of the Fresnel scale to the relative velocity perpendicular to the line of sight between the observer and the KBO. Since the relative velocity is usually dominated by the Earth's velocity around the Sun, which is 30 km s −1 , typical occultations only last of order of a tenth of a second.Extensive ground based efforts have been conducted to look for optical occultations (10; 9; 14; 15). To date, these visible searches have announced no detections in the region of the Kuiper belt (30-60 AU), but one of these quests claims to have detected some events beyond 100 AU and at about 15 AU (10). Unfortunately, ground based surveys may suffer from a high rate of false-positives due to atmospheric scintillation, and lack the stability of space based platforms. The ground ...

Relationship between Size and Function of Natural Substance Particles

“…Therefore, here we define the upper limit of MPs based on the scale of the subject that we can see its contour of the whole body as well as recognize its details, such as a stone that we can see its whole body as well as its thin particles on the surface. In addition, the smallest celestial body is seen on the scale of 10 2 m [13], which may also be considered as the basis for the definition of the upper limit of MPs. From the viewpoint of particles, the macroscopic bodies are merely large particles, namely the so-called MPs.…”

“…What is different from other particles is only that they have much larger sizes. The lower limit of CePs is defined as 10 2 m because the known smallest celestial body has a diameter of 975 m [13], namely about 10 3 m. The upper limit cannot be defined presently. The sun is the largest particles in solar system where we live.…”

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

“…As the sky surface density of KBOs is near zero at such high ecliptic latitudes (Volk & Malhotra, 2017, Figure 10), data collected in this regime cannot be used to constrain KBO surface density, but instead provides a control for other measurements taken near the ecliptic. For example, event rate measurements at |β| ą 20h ave been used by previous surveys (e.g., Schlichting et al, 2009) as zero-detection control samples to establish false positive rates.…”

“…TAOS established an upper limit of 3.34 to 3.82 on the index q of the small-KBO power law ( dn dR 9R´q), with the size distribution of small KBOs normalized using surface densities of 38.0 deg´2 (Fuentes et al, 2009) and 5.4 deg´2 (Fraser & Kavelaars, 2008) at the break in the size-frequency distribution (R " 45 km), respectively (Zhang et al, 2013). Furthermore, some surveys have produced modelindependent constraints at specific KBO diameters 2 , such as Bianco et al (2009), Bickerton et al (2008, Jones et al (2008) (see Bianco et al, 2009, Figure 12) and Schlichting et al (2009).…”

“…A potential detection of a KBO occultation was obtained by Schlichting et al (2009), who analyzed 12,000 star hours of Hubble Space Telescope archival data taken at a cadence of 40 Hz. A follow-up survey of 19,500 additional star hours yielded a second occultation candidate (Schlichting et al, 2012).…”