Photometry of Kuiper Belt Object (486958) Arrokoth from New Horizons LORRI
Jason D. Hofgartner, Bonnie J. Buratti, Susan D. Benecchi, Ross A. Beyer, Andrew Cheng, James T. Keane, Tod R. Lauer, Catherine B. Olkin, Joel W. Parker, Kelsi … 展开作者
Jason D. Hofgartner, Bonnie J. Buratti, Susan D. Benecchi, Ross A. Beyer, Andrew Cheng, James T. Keane, Tod R. Lauer, Catherine B. Olkin, Joel W. Parker, Kelsi N. Singer, John R. Spencer, S. Alan Stern, Anne J. Verbiscer, Harold A. Weaver, New Horizons Geology, Geophysics Team, New Horizons LORRI Team
On January 1st 2019, the New Horizons spacecraft flew by the classical Kuiper belt object (486958) Arrokoth (provisionally designated 2014 MU69), possibly the most primitive object ever explored by a spacecraft. The I/F of Arrokoth is analyzed and fit with a photometric function that is a linear combination of the Lommel-Seeliger (lunar) and Lambert photometric functions. Arrokoth has a geometric albedo of p_V = 0.21_(-0.04)^(+0.05) at a wavelength of 550 nm and ~0.24 at 610 nm. Arrokoth's geometric albedo is greater than the median but consistent with a distribution of cold classical Kuiper belt objects whose geometric albedos were determined by fitting a thermal model to radiometric observations. Thus, Arrokoth's geometric albedo adds to the orbital and spectral evidence that it is a cold classical Kuiper belt object. Maps of the normal reflectance and hemispherical albedo of Arrokoth are presented. The normal reflectance of Arrokoth's surface varies with location, ranging from ~0.10-0.40 at 610 nm with an approximately Gaussian distribution. Both Arrokoth's extrema dark and extrema bright surfaces are correlated to topographic depressions. Arrokoth has a bilobate shape and the two lobes have similar normal reflectance distributions: both are approximately Gaussian, peak at ~0.25 at 610 nm, and range from ~0.10-0.40, which is consistent with co-formation and co-evolution of the two lobes. The hemispherical albedo of Arrokoth varies substantially with both incidence angle and location, the average hemispherical albedo at 610 nm is 0.063 +/- 0.015. The Bond albedo of Arrokoth at 610 nm is 0.062 +/- 0.015.
The New Horizons space probe led the first close flyby of one of the most primordial and distant objects left over from the formation of the solar system, the contact binary Kuiper Belt object (486958) Arrokoth, which is composed of two progenitors, the lobes nicknamed Ultima and Thule. In the current work, we investigated Arrokoth's surface in detail to identify the location of equilibrium points and also explore each lobe's individual dynamic features. We assume Arrokoth's irregular shape as a homogeneous polyhedra contact binary. We numerically explore its dynamic characteristics by computi…
The contact binary Kuiper Belt object (486958) Arrokoth, targeted by New Horizons mission, has a unique slope pattern, which is a result of its irregular bilobate surface shape and high spin period. Thus, some peculiar topographic regions on its surface are predisposed to lose or accumulate material, as a long circular depression feature, an impact crater called Maryland, on its small lobe. The equilibrium points of Arrokoth are also directly related to the structure of the environment near these surface features. In this work, we performed numerical simulations around Arrokoth to explore the …
The New Horizons spacecraft's encounter with the cold classical Kuiper belt object (486958) Arrokoth (formerly 2014 MU69) revealed a contact-binary planetesimal. We investigate how it formed, finding it is the product of a gentle, low-speed merger in the early Solar System. Its two lenticular lobes suggest low-velocity accumulation of numerous smaller planetesimals within a gravitationally collapsing, solid particle cloud. The geometric alignment of the lobes indicates the lobes were a co-orbiting binary that experienced angular momentum loss and subsequent merger, possibly due to dynamical fr…
One of the most striking and curious features of the small Kuiper Belt Object (KB), Arrokoth, explored by New Horizons, is the bright, annular neck it exhibits at the junction between its two lobes. Here we summarize past reported findings regarding the properties of this feature and report new findings regarding its dimensions, reflectivity and color, shape profile, and its lack of identifiable craters. We conclude by enumerating possible origin scenarios for this unusual feature. New results include a new measurement of the observed neck area of 8+/-1.5 km2, a total neck surface area of 32 k…
We combine several constraints provided by the crater records on Arrokoth and the worlds of the Pluto system to compute the size-frequency distribution (SFD) of the crater production function for craters with diameter D<10km. For this purpose, we use a Kuiper belt objects (KBO) population model calibrated on telescopic surveys, that describes also the evolution of the KBO population during the early Solar System. We further calibrate this model using the crater record on Pluto, Charon and Nix. Using this model, we compute the impact probability on Arrokoth, integrated over the age of the Solar…
The outer Solar System object (486958) Arrokoth (provisional designation 2014 MU$_{69}$) has been largely undisturbed since its formation. We study its surface composition using data collected by the New Horizons spacecraft. Methanol ice is present along with organic material, which may have formed through radiation of simple molecules. Water ice was not detected. This composition indicates hydrogenation of carbon monoxide-rich ice and/ or energetic processing of methane condensed on water ice grains in the cold, outer edge of the early Solar System. There are only small regional variations in…
The New Horizons mission has returned stunning images of the bilobate Kuiper belt object (486958) Arrokoth. It is a contact binary, formed from two intact and relatively undisturbed predecessor objects joined by a narrow contact region. We use a version of pkdgrav, an N-body code that allows for soft-sphere collisions between particles, to model a variety of possible merger scenarios with the aim of constraining how Arrokoth may have evolved from two Kuiper belt objects into its current contact binary configuration. We find that the impact must have been quite slow (less than 5 m/s) and grazin…
The New Horizons spacecraft's flyby of Kuiper Belt Object (KBO) (486958) Arrokoth revealed a bilobed shape with highly flattened lobes both aligned to its equatorial plane, and a rotational axis almost aligned to the orbital plane (obliquity ~99 deg). Arrokoth belongs to the Cold Classical Kuiper Belt Object population that occupies dynamically undisturbed orbits around the Sun, and as such, is a primitive object that formed in situ. Therefore, whether its shape is primordial or evolutionary carries important implications for understanding the evolution of both KBOs and potentially their dynam…
The Cold Classical Kuiper Belt, a class of small bodies in undisturbed orbits beyond Neptune, are primitive objects preserving information about Solar System formation. The New Horizons spacecraft flew past one of these objects, the 36 km long contact binary (486958) Arrokoth (2014 MU69), in January 2019. Images from the flyby show that Arrokoth has no detectable rings, and no satellites (larger than 180 meters diameter) within a radius of 8000 km, and has a lightly-cratered smooth surface with complex geological features, unlike those on previously visited Solar System bodies. The density of …
Southwest Research Institute（西南研究所）；Lunar and Planetary Institute（月球与行星研究所）；University of Virginia（弗吉尼亚大学）；Planetary Science Institute（行星科学研究所）；Johns Hopkins University Applied Physics Laboratory（约翰斯·霍普金斯大学应用物理实验室）
NASA's New Horizons spacecraft observed (15810) 1994 JR$_1$, a 3:2 resonant Kupier Belt Object (KBO), using the LOng Range Reconnaissance Imager (LORRI) on November 2, 2015 from a distance of 1.85 AU, and again on April 7, 2016 from a distance of 0.71 AU. These were the first close observations of any KBO other than Pluto. Combining ground-based and Hubble Space Telecope (HST) observations at small phase angles and the LORRI observations at higher phase angles, we produced the first disk-integrated solar phase curve of a typical KBO from $α$=0.6-58$^\circ$. Observations at these geometries, at…
The LOng Range Reconnaissance Imager (LORRI) is a panchromatic (360--910 nm), narrow-angle (field of view = 0.29 deg), high spatial resolution (pixel scale = 1.02 arcsec) visible light imager used on NASA's New Horizons (NH) mission for both science observations and optical navigation. Calibration observations began several months after the NH launch on 2006 January 19 and have been repeated annually throughout the course of the mission, which is ongoing. This paper describes the in-flight LORRI calibration measurements, and the results derived from our analysis of the calibration data. LORRI …
The exploration of the Pluto-Charon system by the New Horizons spacecraft represents the first opportunity to understand the distribution of albedo and other photometric properties of the surfaces of objects in the Solar System's "Third Zone" of distant ice-rich bodies. Images of the entire illuminated surface of Pluto and Charon obtained by the Long Range Reconnaissance Imager (LORRI) camera provide a global map of Pluto that reveals surface albedo variegations larger than any other Solar System world except for Saturn's moon Iapetus. Normal reflectances on Pluto range from 0.08-1.0, and the …
Following its flyby and first imaging the Pluto-Charon binary, the New Horizons spacecraft visited the Kuiper-Belt-Object (KBO) (486958) 2014 MU69 (Arrokoth). Imaging showed MU69 to be a contact-binary, made of two individual lobes connected by a narrow neck, rotating at low spin period (15.92 h), and having high obliquity (~98 deg), similar to other KBO contact-binaries inferred through photometric observations. The origin of such peculiar configurations is puzzling, and all scenarios suggested for the origins of contact-binaries fail to reproduce such properties and their likely high frequen…
Comets and small Kuiper belt objects are considered to be among the most primitive objects in the solar system as comets like C/1995 O1 Hale-Bopp are rich in highly volatile ices like CO. It has been suggested that early in the solar system evolution the precursors of both groups, the so-called icy planetesimals, were modified by both short-lived radiogenic heating and collisional heating. Here we employ 2D finite-difference numerical models to study the internal thermal evolution of these objects, where we vary formation time, radius and rock-to-ice mass fraction. Additionally we perform 3D S…
We discuss in a thermodynamic, geologically empirical way the long-term nature of the stable majority ices that could be present in Kuiper Belt Object 2014 MU69 after its 4.6 Gyr residence in the EKB as a cold classical object. Considering the stability versus sublimation into vacuum for the suite of ices commonly found on comets, Centaurs, and KBOs at the average ~40K sunlit surface temperature of MU69 over Myr to Gyr, we find only 3 common ices that are truly refractory: HCN, CH3OH, and H2O (in order of increasing stability). NH3 and H2CO ices are marginally stable and may be removed by any …
We present the results from four stellar occultations by (486958) Arrokoth, the flyby target of the New Horizons extended mission. Three of the four efforts led to positive detections of the body, and all constrained the presence of rings and other debris, finding none. Twenty-five mobile stations were deployed for 2017 June 3 and augmented by fixed telescopes. There were no positive detections from this effort. The event on 2017 July 10 was observed by SOFIA with one very short chord. Twenty-four deployed stations on 2017 July 17 resulted in five chords that clearly showed a complicated shape…
Using the New Horizons LORRI camera, we searched for satellites near five Kuiper belt objects (KBOs): four cold classicals (CCs: 2011 JY31, 2014 OS393, 2014 PN70, 2011 HZ102) and one scattered disk object (SD: 2011 HK103). These objects were observed at distances of 0.092-0.290 au from the New Horizons spacecraft, achieving spatial resolutions of 136-430 km (resolution is ~2 camera pixels), much higher than possible from any other facilities. Here we report that CC 2011 JY31 is a binary system with roughly equal brightness components, CC 2014 OS393 is likely an equal brightness binary system, …
