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The HST Lightcurve of (486958) 2014 MU69 | | Susan Benecchi
; Simon Porter
; John Spencer
; Anne Verbiscer
; Keith Noll
; S. A. Stern
; Marc Buie
; Amanda Zangari
; Alex Parker
; | | Date: |
12 Dec 2018 | | Abstract: | We report HST lightcurve observations of the New Horizons spacecraft
encounter Kuiper Belt object (KBO) (486958) 2014 MU69 acquired near opposition
in July 2017. In order to plan the optimum flyby sequence the New Horizons
mission planners needed to learn as much as possible about the target in
advance of the encounter. Specifically, encounter timing could be adjusted to
accommodate a highly elongated, binary, or rapidly rotating target. HST
astrometric (Porter et al. 2018) and stellar occultation (Buie et al. 2018)
observations constrained MU69’s orbit and diameter (21-41 km for an albedo of
0.15-0.04), respectively. Photometry from the astrometric dataset suggested a
rotational lightcurve amplitude of ge 0.3 mags, but they did not determine the
period or provide shape information. To that end we strategically spaced 24 HST
orbits over 9 days to investigate rotation periods from approximately 3-100
hours and to better constrain the lightcurve amplitude. Until New Horizons
detected MU69 in its optical navigation images in August 2018, this HST
lightcurve campaign provided the most accurate photometry to date. The mean
variation in our data is 0.15 magnitudes which suggests that MU69 is either
nearly spherical (a:b axis ratio of 1:1.15), or its pole vector is pointed near
the line of sight to Earth; this interpretation does not preclude a
near-contact binary or bi-lobed object. However, image stacks do conclude that
MU69 does not have a binary companion ge 2000km with a sensitivity to 29th
magnitude (an object a few km in size). Our data are not of sufficient signal
to noise to uniquely determine the period or amplitude so we do over analyze
the data, however, they did provide the necessary information for spacecraft
planning. We report with confidence that MU69 is not rapidly rotating AND
highly elongated (which we define as a lightcurve amplitude ge 0.5 magnitude). | | Source: | arXiv, 1812.4758 | | Services: | Forum | Review | PDF | Favorites | |
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