Col-OSSOS: Investigating Outlying Surfaces within the Kuiper Belt's Neutral Coloured Objects

<p>Within the outer Solar System exists the Kuiper belt. This Kuiper belt is made up of many icy planetesimals, the remaining relics of planet-forming bodies that failed to evolve into a planet beyond Neptune. The smaller members of the Kuiper belt (with <em>r</em> mag > 22) generally show linear and featureless spectra. Additionally, due to the dimness of these objects observing their spectra can be particularly difficult. Therefore, broadband photometry is often used to characterise their surfaces. The broadband photometry can be used as a proxy for composition, as it provides enough information to characterise the optical and near-infrared spectral slopes ofthese Kuiper Belt Object (KBO) surfaces.</p> <p>The Colours of the Outer Solar System Origins Survey (Col-OSSOS, Schwamb et al., 2019) took near-simultaneous <em>g-</em>, <em>r-</em> and <em>J-band</em> broadband photometry of a sample of KBOs with unprecedented precision using the Gemini North telescope. As with previous colour surveys (e.g. Tegler et al., 2016), they showed abimodal colour distribution in optical / near-infrared colours for the dynamically ‘hot’ population. We split this colour distribution into the ‘neutral’ coloured population with <em>(</em><em>g−r</em><em>)</em> < 0.75 and the ‘red’ coloured populationwith <em>(</em><em>g−r</em><em>)</em> ≥ 0.75.</p> <p>The preciseness of the colour measurements of Col-OSSOS has allowed the identification of several KBOs with outlying surface colours. These objects separated out from the rest of the neutral cloud in <em>(</em><em>g−r</em><em>)</em> versus <em>(r−J</em><em>)</em> colours, with <em>(</em><em>g−r</em><em>)</em> colour near solar colour. Using the Gemini North telescope in Hawaii we have taken extra photometry in the <em>i</em><em>−</em> and <em>z−</em><em>bands</em> for three of these objects (2013 JE64, 2013 JR65 and 2014 UL225). These additional filter observations will allow us to identify any possible broadband absorption features on these object’s surfaces that may have caused their outlying surface colours. Asteroid interloper 2004 EW95 (Seccull et al., 2018), along with some Jupiter Trojans and C-type asteroids (Bus & Binzel, 2002; DeMeo & Carry,2013) have been shown to have similar near solar neutral surfaces. In this presentation we will report resultsof the <em>griz</em> photometry of 2013 JE64, 2013 JR65 and 2014 UL225. We will make comparisons between these results and the photometry of previously identified outlying KBOs and comment on any possible similarities.</p> <p><strong>References</strong></p> <p>Bus, S. J., & Binzel, R. P. 2002, Icarus, 158, 146<br />DeMeo, F. E., & Carry, B. 2013, Icarus, 226, 723<br />Schwamb, M. E., Bannister, M. T., Marsset, M., et al. 2019, ApJS, 243, 12<br />Seccull, T., Fraser, W. C., Puzia, T. H., Brown, M. E., & Schönebeck, F. 2018, ApJ, Letters, 855, L26<br />Tegler, S. C., Romanishin, W., Consolmagno, G. J., & J., S. 2016, AJ, 152, 210</p>

Organic Components of Small Bodies in the Outer Solar System: Some Results of the New Horizons Mission

The close encounters of the Pluto–Charon system and the Kuiper Belt object Arrokoth (formerly 2014 MU69) by NASA’s New Horizons spacecraft in 2015 and 2019, respectively, have given new perspectives on the most distant planetary bodies yet explored. These bodies are key indicators of the composition, chemistry, and dynamics of the outer regions of the Solar System’s nascent environment. Pluto and Charon reveal characteristics of the largest Kuiper Belt objects formed in the dynamically evolving solar nebula inward of ~30 AU, while the much smaller Arrokoth is a largely undisturbed relic of accretion at ~45 AU. The surfaces of Pluto and Charon are covered with volatile and refractory ices and organic components, and have been shaped by geological activity. On Pluto, N2, CO and CH4 are exchanged between the atmosphere and surface as gaseous and condensed phases on diurnal, seasonal and longer timescales, while Charon’s surface is primarily inert H2O ice with an ammoniated component and a polar region colored with a macromolecular organic deposit. Arrokoth is revealed as a fused binary body in a relatively benign space environment where it originated and has remained for the age of the Solar System. Its surface is a mix of CH3OH ice, a red-orange pigment of presumed complex organic material, and possibly other undetected components.

Surface dynamics, equilibrium points and individual lobes of the Kuiper Belt object (486958) Arrokoth

ABSTRACT 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. This is composed of two progenitors, the lobes called Ultima and Thule. In the current work, we investigate Arrokoth’s surface in detail to identify the location of equilibrium points and also we explore each lobe’s individual dynamic features. We assume that Arrokoth’s irregular shape is a homogeneous polyhedra contact binary. We explore its dynamic characteristics numerically by computing its irregular binary geopotential in order to study its quantities, such as geometric height, oblateness, ellipticity and zero-power curves. The stability of Arrokoth Hill was also explored through zero-velocity curves. Arrokoth’s external equilibrium points have no radial symmetry due to its highly irregular shape. We identified even equilibrium points concerning its shape and spin rate: i.e. four unstable external equilibrium points and three inner equilibrium points, where two points are linearly stable, with an unstable central point that has a slight offset from its centroid. Moreover, the large and small lobes each have five equilibrium points with different topological structures from those found in Arrokoth. Our results also indicate that the equatorial region of Arrokoth’s lobes is an unstable area due to the high rotation period, while its polar locations are stable resting sites for surface particles. Finally, the zero-power curves indicate the locations around Arrokoth where massless particles experience enhancing and receding orbital energy.

The solar nebula origin of (486958) Arrokoth, a primordial contact binary in the Kuiper Belt

The New Horizons spacecraft’s encounter with the cold classical Kuiper Belt object (486958) Arrokoth (provisional designation 2014 MU69) revealed a contact-binary planetesimal. We investigated how Arrokoth formed and found that 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 cloud of solid particles. The geometric alignment of the lobes indicates that they were a co-orbiting binary that experienced angular momentum loss and subsequent merger, possibly because of dynamical friction and collisions within the cloud or later gas drag. Arrokoth’s contact-binary shape was preserved by the benign dynamical and collisional environment of the cold classical Kuiper Belt and therefore informs the accretion processes that operated in the early Solar System.

The geology and geophysics of Kuiper Belt object (486958) Arrokoth

The Cold Classical Kuiper Belt, a class of small bodies in undisturbed orbits beyond Neptune, is composed of primitive objects preserving information about Solar System formation. In January 2019, the New Horizons spacecraft flew past one of these objects, the 36-kilometer-long contact binary (486958) Arrokoth (provisional designation 2014 MU69). Images from the flyby show that Arrokoth has no detectable rings, and no satellites (larger than 180 meters in diameter) within a radius of 8000 kilometers. Arrokoth has a lightly cratered, smooth surface with complex geological features, unlike those on previously visited Solar System bodies. The density of impact craters indicates the surface dates from the formation of the Solar System. The two lobes of the contact binary have closely aligned poles and equators, constraining their accretion mechanism.