Great Expectations: Plans and Predictions for New Horizons Encounter With Kuiper Belt Object 2014 MU<sub>69</sub> (“Ultima Thule”)

Moore, Jeffrey M.; McKinnon, William B.; Cruikshank, D. P.; Gladstone, G. R.; Spencer, J. R.; Stern, S. A.; Weaver, H. A.; Singer, K. N.; Showalter, M. R.; Grundy, W. M.; Beyer, R. A.; White, O. L.; Binzel, Richard P.; Buratti, B. J.; Cheng, A. F.; Howett, C. J. A.; Parker, A. H.; Porter, S. B.; Schenk, P.; Throop, H. B.; Verbiscer, A.; Young, L. A.; Benecchi, Susan; Bray, V. J.; Chavez, Carrie L.; Dhingra, Rajani D.; Howard, A. D.; Lauer, Tod R.; Lisse, C. M.; Robbins, S. J.; Runyon, K. D.; Umurhan, O. M.

doi:10.1029/2018gl078996

Cited by 15 publications

(10 citation statements)

References 79 publications

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“…Also, in Thirouin & Sheppard (2019), we report several potential contact binaries showing a large lightcurve amplitude but unfortunately without a full lightcurve allowing us to classify them as likely/confirmed contact binaries, and thus to be conservative we consider them as potential contact binaries as more data are needed to classify them. Finally, the flyby of 2014 MU 69 by the NASA New Horizons spacecraft and its stellar occultation confirmed that this dynamically Cold Classical trans-Neptunian object (TNO) is also a contact binary (Stern et al 2019;Moore et al 2018). Currently, the census of contact binaries is: .…”

Section: Contact Binariesmentioning

confidence: 86%

Colors of Trans-Neptunian Contact Binaries

Thirouin

Sheppard

2019

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The g'r'i' colors of seven likely and potential contact binaries in the Kuiper belt were acquired with the Magellan-Baade telescope and combined with colors from the literature to understand contact binary surfaces. The likely and potential contact binaries discovered in the dynamically Cold Classical population display very-red/ultra-red colors. Such a color is common in this sub-population and infers that the Cold Classical contact binaries were formed in-situ. The likely contact binaries found in several mean motion resonances with Neptune have colors from moderately to ultra-red suggesting different formation regions. Among the nine contact binaries discovered in resonances, five have veryred/ultra-red colors and four have moderately-red surfaces. Based on the very-red/ultra-red colors and low to moderate inclination of the contact binaries in resonances, these contact binaries are maybe escaped dynamically Cold Classicals that are now trapped in resonances. Moderately-red surfaces are common in diverse sub-populations of the Kuiper belt and thus pinpointing their origin is difficult though they are most likely captured objects formed in the giant planet area. Finally, for the contact binary population we report an anti-correlation between inclination and g'-r', as noticed in the rest of this belt. We also have hints for trends between eccentricity, perihelion distance, rotational period and g'-r', but as we are still dealing with a limited sample, additional data are required to confirm them.

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Section: Contact Binariesmentioning

confidence: 86%

Colors of Trans-Neptunian Contact Binaries

Thirouin

Sheppard

2019

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“…The upcoming flyby of the New Horizons spacecraft by the cold classical transneptunian object (TNO) 2014 MU69 (hereafter referred to as MU69) will offer the first up-close look (sub-km resolution) of a small outer Solar System body in its formation environment, and will provide the first opportunity to observe a high-resolution cratered surface of a TNO other than those in the Pluto system, imaged by New Horizons in July 2015 (Stern et al, 2015;Moore et al, 2018).…”

Section: Introductionmentioning

confidence: 99%

Crater Density Predictions for New Horizons Flyby Target 2014 MU69

Greenstreet

Gladman

McKinnon³

et al. 2019

ApJL

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In preparation for the Jan 1/2019 encounter between the New Horizons spacecraft and the Kuiper Belt object 2014 MU69, we provide estimates of the expected impact crater surface density on the Kuiper Belt object. Using the observed crater fields on Charon and Pluto down to the resolution limit of the 2015 New Horizons flyby of those bodies and estimates of the orbital distribution of the crater-forming projectiles, we calculate the number of craters per unit area formed as a function of the time a surface on 2014 MU69 has been exposed to bombardment. We find that if the shallow cratersize distribution from 1-15 km exhibited on Pluto and Charon is indeed due to the sizes of Kuiper Belt projectiles, 2014 MU69 should exhibit a surface that is only lightly cratered below 1 km scale, despite being bombarded for ∼ 4 billion years. Its surface should therefore be more clearly indicative of its accretionary environment. In addition, this object may the first observed for which the majority of the bombardment is from exogenic projectiles moving less than or near the speed of sound in the target materials, implying morphologies more akin to secondary craters elsewhere in the Solar System.Lastly, if the shallow Kuiper Belt size distribution implied from the Pluto and Charon imaging is confirmed at MU69, then we conclude that this size distribution is a preserved relic of its state ≃4.5 Gyr ago and provides a direct constraint on the planetesimal formation process itself.

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“…and 𝑚𝑅 4 ' 𝜔6 , respectively, where m and Re are the total mass and equivalent spherical radius. The normalized spin and angular momentum for Arrokoth are ~0.29 and ~0.36, respectively, assuming a mass ratio of 2:1 for LL and SL and r = 500 kg m -3 for both lobes.…”

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

McKinnon

Richardson²,

Marohnic³

et al. 2020

Science

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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 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 so informs the accretion processes that operated in the early Solar System.Main Text: Following its encounter with Pluto in 2015 (1), the New Horizons spacecraft continued further into the Kuiper belt (2). This included a flyby of (486958) Arrokoth (also informally known as Ultima Thule), discovered in a dedicated Hubble Space Telescope campaign (3). Arrokoth's orbit has a semimajor axis a⨀ = 44.2 astronomical units (au), Submitted Manuscript: Confidential 3 eccentricity e = 0.037, and inclination i = 2.54°, making it a member of the cold classical Kuiper belt (CCKB), a reservoir of mainly small bodies on dynamically cold orbits, i.e., those with lowto-moderate e and low i (typically i < 5°), in the outer Solar System (4). CCKB objects have a steeper size-frequency distribution, higher binary fraction, higher albedos, and redder optical colors than the dynamically hot and Neptune-resonant populations of the Kuiper belt, implying a distinct formation mechanism and/or evolutionary history (4). CCKB objects are thought to have formed in place and remained largely undisturbed by the migration of the Solar System's giant planets (4, 5, 6), making them unperturbed remnants of the original protoplanetary disk.The encounter showed Arrokoth is a bi-lobed object, consisting of two discrete, quasiellipsoidal lobes (equivalent spherical diameters 15.9 and 12.9 km, respectively) joined at a narrow contact area or "neck" (Fig. 1) (7,8). We interpret this geometric, co-joined object as a contact binary, i.e., two formerly separate objects that have gravitated towards each other until they touch. The larger lobe (hereafter LL) is more oblate than the smaller lobe (hereafter SL) (8).Arrokoth rotates with a 15.92-hr period at an obliquity of 99° (the angle between its rotation axis and heliocentric orbital plane). The short axes of both lobes are aligned to within a few degrees of each other and with the spin axis of the body as a whole (8). The average visible and nearinfrared colors of both lobes are indistinguishable (9). Near-infrared spectral absorptions on both lobes indicate the presence of methanol ice-a common, relatively thermally stable component (for an ice) of cometary bodies and extrasolar protoplanetary disks (10). The very red optical c...

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Great Expectations: Plans and Predictions for New Horizons Encounter With Kuiper Belt Object 2014 MU₆₉ (“Ultima Thule”)

Cited by 15 publications

References 79 publications

Colors of Trans-Neptunian Contact Binaries

Colors of Trans-Neptunian Contact Binaries

Crater Density Predictions for New Horizons Flyby Target 2014 MU69

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

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Great Expectations: Plans and Predictions for New Horizons Encounter With Kuiper Belt Object 2014 MU69 (“Ultima Thule”)

Cited by 15 publications

References 79 publications

Colors of Trans-Neptunian Contact Binaries

Colors of Trans-Neptunian Contact Binaries

Crater Density Predictions for New Horizons Flyby Target 2014 MU69

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

Contact Info

Product

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Great Expectations: Plans and Predictions for New Horizons Encounter With Kuiper Belt Object 2014 MU₆₉ (“Ultima Thule”)