New Horizons: Long-range Kuiper Belt targets observed by the Hubble Space Telescope

Abstract

We report on Hubble Space Telescope (HST) observations of three Kuiper Belt Objects (KBOs), discovered in our dedicated ground-based search campaign, that are candidates for long-range observations from the New Horizons spacecraft: 2011 JY 31 , 2011 HZ 102 , and 2013 LU 35 . Astrometry with HST enables both current and future critical accuracy improvements for orbit precision, required for possible New Horizons observations, beyond what can be obtained from the ground. Photometric colors of all three objects are red, typical of the Cold Classical dynamical population within which they reside; they are also the faintest KBOs to have had their colors measured. None are observed to be binary with HST above separations of ~0.02 arcsec (~700 km at 44 AU) and Δm ≤ 0.5. 10 -170 km), is one of the largest and most complex members of the Kuiper Belt (Jewitt & Luu, 1993). This region has more than 1700 objects that have been discovered and cataloged, and is estimated to contain ~10 5 objects having diameters larger than d~100 km (Petit et al. 2011). The physical properties of smaller (d~30-300 km), less atypical Kuiper Belt Objects (KBOs) provide important points of comparison and context for understanding the Pluto system and its relationship to the larger Kuiper Belt. A flyby of a KBO and studies of other encounterable objects have always been key goals for the New Horizons mission beyond the Pluto encounter as identified for the NASA KBO/Pluto mission (which became New Horizons) in the 2002 Planetary Decadal Survey (Belton et al. 2002). The New Horizons spacecraft and mission was designed, therefore, to allow redirection to one or more KBOs between 2017 and 2021(Stern 2008Spencer et al. 2003) provided that a suitable candidate can be identified. This is likely to be the only opportunity in our lifetimes to encounter a KBO other than Pluto.Because precise orbits for flyby and long-range candidates are critical to the success of the New Horizons extended mission, we present in this paper Hubble Space Telescope (HST) follow-up observations of candidate targets exploiting HST's sensitivity, resolution, and PSF stability. These HST observations also allow us to make basic color measurements and to search for binary companions down to ~0.02 arcseconds in angular separation at the time of the observations. Identifying Potentially Encounterable KBOsThe KBOs that are potentially encounterable by New Horizons are limited to those with orbits that place them within reach of the remaining Δv capability of the spacecraft, currently estimated to be Δv≈ 130 m s -1 . This restriction means that by far the most likely candidate target(s) will be a member of the low-eccentricity, low-inclination Cold Classical subpopulation. In 2004 a ground-based search for bright objects (m R ≥ 24.0) was conducted over a wide area of sky (a few degrees) through which objects that will be in the New Horizons spacecraft trajectory during the optimal KBO encounter dates were located. This is defined by projecting the nominal trajectory of New ...

The color and binarity of (486958) 2014 MU69 and other long-range New Horizons Kuiper Belt targets

“…COLOR, BINARITY, SIZE AND VARIABILITY FINDINGS Table 3 lists the observed colors of the KBOs from this program. In Figure 3 we then compare this newly obtained data with 145 KBO colors that have been previously measured using the same HST filters (Benecchi et al 2009;Fraser et al 2012;Benecchi et al 2015). The F606W-F814W colors (a proxy for V-I) plotted span a wide range from 0.5 < F606W-F814W < 1.3.…”

“…Color results for all long-range New Horizons targets with HST colors compared with the colors of all other KBOs that have been measured in the same HST filters (from Benecchi et al 2009, Fuentes et al 2010Fraser et al 2012 andBenecchi et al 2015) with respect to their direct F606W magnitudes. Plotted along the top is an estimate of the effective diameters for these objects following the formulation of Bowell et al (1989) d = 10((6.259−0.4·HF606W −log r)/2) km and assuming an albedo, r; we assume r = 0.12.…”

“…In this paper we report optical color measurements obtained with the Hubble Space Telescope (HST) for 8 of the KBOs that New Horizons has, or will be observing. Three additional long-range targets were previously reported in Benecchi et al 2015. These objects are not all inclusive of the distant KBOs to be observed by New Horizons, but are the objects which had been selected for distant observation at the time of the Cycle 23 proposal deadline and which did not have any previous HST color measurements.…”

“…The location of the objects from this work andBenecchi et al (2015) are highlighted in as black triangles with respect to the background Classical Kuiper Belt in a,e and i space. For clarity, no Resonant or Scattered objects are plotted, although the Resonant locations are show as vertical dashed lines.…”

Megacam: A Wide-Field CCD Imager for the MMT and Magellan

“…While the secondary targets for New Horizons are even fainter and required the use of HST to discover, the Megacam images can be used to extend the orbital arcs of those targets. The Megacam search yielded the discovery of a new Neptune Trojan (Parker et al 2013) and identified targets that will be examined at long range with New Horizons (Benecchi et al 2015). The Megacam search data, in combination with the HST data, will also be used in refining our understanding of the size distribution of small Kuiper belt objects.…”