According to a team of researchers led by Southwest Research Institute scientist Simon Porter, Kuiper belt objects (KBO) JR1 and MU69 are as red as, if not redder than, the dwarf planet Pluto.
Artist’s impression of New Horizons encountering a Kuiper belt object. Image credit: NASA / JHUAPL / SwRI / Alex Parker.
JR1 (full name 1994 JR1) is a minor planet about 90 miles (150 km) in diameter.
This object is currently an accidental quasi-satellite of Pluto and it will remain as such for 350,000 years.
It is also a so-called plutino, a trans-Neptunian object in 2:3 mean-motion resonance with the gas giant Neptune.
“JR1 was observed by NASA’s New Horizons spacecraft using the LOng Range Reconnaissance Imager (LORRI) on November 2, 2015 from a distance of 1.85 AU (astronomical units), and again on April 7, 2016 from a distance of 0.71 AU,” Dr. Porter and co-authors said.
“These were the first close observations of any KBO other than Pluto, and the first ever of a small KBO at close range.”
This false color image shows the minor planet/plutino 1994 JR1 (arrow). Image credit: NASA / Johns Hopkins University Applied Physics Laboratory / Southwest Research Institute.
“Combining ground-based and Hubble observations at small phase angles and the LORRI observations at higher phase angles, we produced the first disk-integrated solar phase curve of a typical in-situ KBO from 0.6 to 58 degrees phase angle. Observations at these geometries, a range only attainable using a spacecraft in the outer Solar System, constrain surface properties such as macroscopic roughness and the single particle phase function,” they said.
“JR1 is currently 2.7 AU from Pluto. Our astrometric points enable high-precision orbit determination and integrations which show that it comes this close to Pluto every 2.4 million years, causing Pluto to perturb JR1.”
“During the November spacecraft observation, the KBO was simultaneously observed using the NASA/ ESA Hubble Space Telescope in two colors, confirming its very red spectral slope.”
Hubble images of 2014 MU69 taken on June 24, 2014. The images were taken at 10-min intervals. The positions of 2014 MU69 in the images are shown by the green circles. Image credit: NASA / ESA / SwRI / JHU / APL / New Horizons KBO Search Team.
The Hubble data also suggest that MU69 (full name 2014 MU69), a small KBO about a billion miles (1.6 billion km) beyond Pluto and the next target for New Horizons, has the similar color as JR1.
MU69 is actually the smallest KBO to have its color measured — and Dr. Porter and his colleagues have used that data to confirm the object is part of the so-called cold classical region of the Kuiper Belt, which is believed to contain some of the oldest, most prehistoric material in the Solar System.
“The reddish color tells us the type of KBO MU69 is,” said New Horizons team member Dr. Amanda Zangari, also from Southwest Research Institute.
“The data confirms that on New Year’s Day 2019, New Horizons will be looking at one of the ancient building blocks of the planets.”
The researchers presented their findings this week at the joint 48th annual meeting of the Division for Planetary Sciences of the American Astronomical Society and 11th annual European Planetary Science Congress in Pasadena, California.
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Simon Porter et al. 2016. The First High-Phase Observations of a KBO: New Horizons Imaging of (15810) 1994 JR 1 from the Kuiper Belt. DPS48/EPSC11, abstract #113.09
