Investigating solar system evolution by identifying and characterizing binary trojan and hilda asteroids the primary goal of this proposal is to help constrain the dynamical evolution of the solar…

This is a $471,532.60 grant awarded by NASA to the Planetary Science Institute (PSI), a non-profit research organization based in Tucson, Arizona. The grant is for a project titled "Investigating Solar System Evolution by Identifying and Characterizing Binary Trojan and Hilda Asteroids." The primary goal is to help constrain the dynamical evolution of the solar system by identifying and characterizing binary asteroids in the Jovian Trojan and Hilda asteroid populations. This will involve conducting a systematic survey to confirm binary candidates identified in previous research and then using the binary properties to infer the density and formation environment of these asteroid groups. The results will provide insights into the history of giant planet migration in the early solar system. The grant does not have a set-aside designation, reflecting PSI's competitive capabilities in planetary science research. This aligns with NASA's broader strategic objectives in planetary science and expanding our scientific understanding of the solar system.

Investigating solar system evolution by identifying and characterizing binary trojan and hilda asteroids the primary goal of this proposal is to help constrain the dynamical evolution of the solar system by identifying and characterizing binary asteroids in the jovian trojan and hilda populations. One of the most debated issues in solar system formation is giant planet migration. The objects thought to be most affected by this migration are jovian trojan asteroids (hereafter, trojans), which LIE in stable orbits around jupiters L4 and L5 lagrange points. Gentle planetary migration models (e.g. marzari & scholl 1998) necessitate that trojans formed in situ, while the nice model of rapid outward giant planet migration suggests that trojans formed in the outer solar system and were scattered into their present orbits (e.g. morbidelli ET AL. 2005). The nice model combined with the grand tack model (e.g. walsh ET AL. 2011) also predicts that trojans and hilda asteroids (in 3:2 orbital resonance with jupiter) share an origin. One observable property that sets powerful constraints on formation location is bulk density, which is more likely to reflect early solar system conditions than surface material altered by irradiation. Low densities are linked to the ICE-rich outer solar system while high densities are consistent with the warmer, inner solar system environment. To help determine the trojan and hilda origin(s), we will identify and characterize their constituent closely separated binary asteroid systems, use the binaries to constrain density, and compare the densities to those of other small bodies. Binary characterization offers the only means of determining density apart from a spacecraft fly-by. We will conduct the first systematic, large-sample study of trojan and hilda binaries. Another major result from this work will be determination of the fraction of trojans and hildas in closely separated binary systems. A difference between binary fractions of two asteroid groups implies different dynamical histories. For example, if one of the trojan clouds has a higher binary fraction than another, then that might support the jumping jupiter model, which proposes that an ICE giant traversed one of the trojan clouds. If the trojan binary fraction is inconsistent with the hilda binary fraction, then perhaps they do not have a common origin as suggested by the nice model. Direct imaging surveys have been able to constrain the widely separated trojan binary population, but only one search for close trojan binaries has been published, and this sample was dominated by large L5 trojans (>20KM; mann ET AL. 2007). The hilda binary fraction has never been explored. Tight binaries with typical rubble pile structures can sometimes be discovered by their rotational light curves, if their orbital planes are in line with earth (e.g. mann ET AL. 2007). All three known close trojan binaries were discovered this way. Using data from the wide-field infrared survey explorer mission, we found 80 trojans and hildas (out of ~1500 searched) with large enough brightness variations to qualify them as possible binaries (sonnett ET AL. 2015). This sample spans a wide range of sizes (~5-100KM) and (for the trojans) equally represents both L4 and L5 clouds. Three of these binary candidates are confirmed through historical data, but the remainder have yet to be confirmed. In the proposed work, we seek to confirm their binarity by densely sampling their rotational light curves, determining the spin period, and comparing binary and single-body models to the light curves while solving for bulk density. We will then debias the resultant binary fraction and compare binary fractions to assess similarities in formation environments and dynamical histories. We have conducted a pilot study (9 targets) and written most of the debiasing code as part of the PI s fellowship, ending in mid-2016. We therefore seek additional support for an observing campaign to targe