Abstract
Abstract Planetesimals inevitably bear the signatures of their natal environment, preserving in their composition a record of the metallicity of their system’s original gas and dust, albeit one altered by the formation processes. When planetesimals are dispersed from their system of origin, this record is carried with them. As each star is likely to contribute at least 1012 interstellar objects (ISOs), the Galaxy’s drifting population of ISOs provides an overview of the properties of its stellar population through time. Using the EAGLE cosmological simulations and models of protoplanetary formation, our modeling predicts an ISO population with a bimodal distribution in their water mass fraction: objects formed in low-metallicity, typically older, systems have a higher water fraction than their counterparts formed in high-metallicity protoplanetary disks, and these water-rich objects comprise the majority of the population. Both detected ISOs seem to belong to the lower water fraction population; these results suggest they come from recently formed systems. We show that the population of ISOs in galaxies with different star formation histories will have different proportions of objects with high and low water fractions. This work suggests that it is possible that the upcoming Vera C. Rubin Observatory Legacy Survey of Space and Time will detect a large enough population of ISOs to place useful constraints on models of protoplanetary disks, as well as galactic structure and evolution.
Highlights
The discovery of 1I/‘Oumuamua (Meech et al 2017) and 2I/Borisov1, the first two interstellar objects detected while passing through our Solar System, has stimulated interest in the properties of the population from which they are drawn
We begin by using the mass and [Fe/H] data provided by the simulations for each star particle in two example galaxies and the models from BB20 described in section 2.1 to predict the water abundance of the interstellar objects (ISOs) in each system
The water fraction of any observed and suitably bright ISO may potentially be determined from their comae, meaning that our model could be tested as more interstellar objects are found
Summary
The discovery of 1I/‘Oumuamua (Meech et al 2017) and 2I/Borisov, the first two interstellar objects detected while passing through our Solar System, has stimulated interest in the properties of the population from which they are drawn. If we want to make predictions about observable quantities, such as the water content of ISOs such as ‘Oumuamua and 2I/Borisov, we need to consider the properties and metallicity of the protoplanetary disk population in the Milky Way. This paper is a first attempt to combine existing models for this purpose. This work demonstrates the interest and importance of this chemical evolutionary approach to predicting the properties of the interstellar object population, and to show how the properties of observed ISOs might constrain the Milky Way’s star formation history. Existing constraints on such models come primarily from observations of stellar abundance. Rubin Observatory’s upcoming Legacy Survey of Space and Time (LSST) (Ivezic et al 2019), we hope that this paper is the beginning of an effort to place interstellar objects passing through our Solar System in the context of Milky Way models
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