Sorcha: A Solar System Survey Simulator for the Legacy Survey of Space and Time

The Vera C. Rubin Observatory Legacy Survey of Space and Time (LSST) will provide an unprecedented dataset to explore the Solar System’s small body inventory. The survey will discover nearly 4 million new Solar System bodies. This is nearly 3 times the current inventory of main-belt asteroids and 6 times more trans-Neptunian objects than are currently known today.  The LSST will go beyond just discovery; with a 10-year baseline, the survey will be able to measure broad-band optical colors and phase curves and capture episodes of cometary activity, orbit changes, rotational breakup events, and rotational brightness variations. Planetesimals are the bricks and mortar left over after the construction of planets. Their compositions, shapes, densities, rotation rates, and orbits help reveal their formation history, the conditions in the planetesimal-forming disk, and the processes active in the Solar System today. LSST will transform our current view of the Solar System and let us peer back into the Solar System’s past like never before.The LSST Solar System Science Collaboration (SSSC) has identified key software products/tools that the Rubin user community must develop to achieve the planetary community’s LSST science goals. Near the top of the SSSC’s software roadmap is a Solar System survey simulator to enable comparisons of model small body orbital and size/brightness distributions to LSST discoveries. For the past several years, we have been developing Sorcha, an open-source community LSST Solar System Survey Simulator handling the scale of the LSST data and the ability to predict on-sky positions for billions of simulated Solar System objects. Sorcha takes a model Solar System small body population and uses the pointing history, observation metadata, and expected Rubin Observatory detection efficiency to output what LSST should find so that the numbers and types of simulated detections can be directly compared to the number and types of real small bodies found in the actual LSST survey.  In this presentation, we will provide an overview of Sorcha, highlight the software design and architecture, provide a demonstration of how Sorcha works, and present key science cases for Sorcha in the context of early LSST Solar System science during the first year of the survey