Altjira: A Potential Hierarchical Triple Trans-Neptunian Object Discovered through non-Keplerian Motion
Abstract
At the edge of the solar system is a region of icy small bodies called the Kuiper Belt. Some of these objects are binaries and when we observe and track their motion, we can then measure many qualities of the objects dynamically, such as mass, orbit, density, and shape. Most of the known objects appear to have only two components, but there is a single known hierarchical triple system with three nearly-equal mass components called (47171) Lempo (Benecchi et al. 2010). A hierarchical triple is so called because when there are three nearly-equal size objects, the only stable configuration is two objects orbiting closely with a third object orbiting further away. Lempo was originally thought to be a binary, but a detailed analysis of the very highest-resolution Hubble Space Telescope images was barely able to resolve the inner binary. So far, no other hierarchical triples have been found in the solar system, due to their rarity and the resolution capabilities of telescopes. Discovering more hierarchical triples will help constrain the streaming instability model of planet formation (Nesvorny et al. 2022). We present evidence for a new hierarchical triple, (148780) Altjira (2001 UQ18), based on non-Keplerian dynamical modeling of the two observed components. Our non-Keplerian analysis includes data over 17 years (including data from ongoing HST Program 17206) which can detect the orbital precession caused by non-spherical shapes and/or unresolved inner binaries. Our analysis shows that Altjira has very strong and statistically significant oblateness (J2), which is best explained as an inner binary. We also find an excellent fit with a hierarchical triple model where the inner binary is unresolved. This potential discovery of the second hierarchical triple in the solar system will help provide new insights into planet formation from these primordial objects.
- Publication:
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American Astronomical Society Meeting Abstracts #243
- Pub Date:
- February 2024
- Bibcode:
- 2024AAS...24334004N