The New Horizons Kuiper Belt Extended Mission

Abstract

The central objective of the New Horizons prime mission was to make the first exploration of Pluto and its system of moons. Following that, New Horizons has been approved for its first extended mission, which has the objectives of extensively studying the Kuiper Belt environment, observing numerous Kuiper Belt Objects (KBOs) and Centaurs in unique ways, and making the first close flyby of the KBO 486958 2014 MU69. This review summarizes the objectives and plans for this approved mission extension, and briefly looks forward to potential objectives for subsequent extended missions by New Horizons.

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

“…Because the rotational period, shape, and rotation axis orientation of Ultima are not known, it is unclear how much of the object will be seen at high resolution. As described in more detail in Stern, Weaver, et al (), resolved observations of Ultima will begin about 2.5–3 days from the closest approach time (~5:33 UTC). Starting at 39 days to closest approach, unresolved images taken by LORRI will be used to search for rings and satellites, especially in regards to potential navigational hazards to the spacecraft.…”

“…The cold classical Kuiper Belt object (CCKBO) 2014 MU 69 (“Ultima”) is the flyby primary target for NASA's New Horizons first Kuiper Belt Extended Mission (Stern, Weaver, et al, ). The cold classical Kuiper Belt consists of objects on nonresonant, low‐eccentricity ( e ), low‐inclination orbits (typically i < 5° to the invariable plane of the solar system), that is, dynamically cold (relatively unexcited) orbits, with heliocentric semimajor axes ( a ) between about 40 and 50 AU.…”

“…A detailed account of this subject is given in Stern, Weaver, et al (); here we briefly summarize: The major science goals of the New Horizons encounter with Ultima are to (1) characterize its global geology, morphology, and rotational characteristics; (2) map its surface composition; (3) search for any satellites and rings and study them as feasible; (4) characterize or constrain its composition and magnitude of any volatile or dust escape from Ultima; (5) characterize the physical properties of its surface; (6) determine its crater size/frequency distribution; (7) constrain its bulk parameters (mass and density); and (8) evaluate evidence of interaction with solar wind. At closest approach New Horizons should pass Ultima at a nominal distance of 3,500 km and at a relative velocity of 14.16 km/s.…”

“…Although these species are stable on the surface at their current temperature, ongoing radiation processing and occasional impacts provide a possible source for a transient atmosphere. Although unlikely, such a transient atmosphere will be searched for by the Alice ultraviolet spectrograph (Stern, Weaver, et al, ), for example, in absorption, using (i) stellar and (ii) solar appulses, and (iii) in emission, using resonantly scattered solar emissions. Dust coma or material otherwise associated with Ultima will be searched for with high phase angle LORRI and MVIC imaging, and with in situ SDC dust detector observations.…”

“…From the disk‐resolved analyses of spatially resolved New Horizons LORRI and MVIC images, the surface of Ultima will be the only CCKBO surface whose microphysical structure (macroscopic roughness and single particle phase function) has been characterized by disk‐resolved photometric analyses. Furthermore, the disk‐integrated solar phase curve derived from New Horizons observations of Ultima will provide context for the interpretation of the disk‐integrated phase curves measured by New Horizons of other, distant CCKBOs (Verbiscer et al, ; Stern, Weaver, et al, ), and enable comparisons between the physical characteristics of particles on their surfaces with those on Ultima's. Comparing Ultima's disk‐integrated phase curve with those of other objects in the OSS should reveal whether particles on its surface preferentially scatter incident visible sunlight in the forward direction like those on both Nix and Hydra (Verbiscer et al, ) and Phoebe (Buratti et al, ).…”