Measuring the outcome of planetesimal formation in the Solar System

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Planetesimals are the building blocks of planets that form in disks of material orbiting around stars.  Determining the range of sizes of the planetesimals that let to formation of planets in our solar system is critical step towards understanding how planets form.  Planetesimals are expected to between 1 and 1000 km in size with different sized objects occurring at different stages during planet formation.  The Kuiper belt is a region of the solar system that is 30 to 1000 times further from the Sun than the Earth.   This zone of the solar system does not currently have any planets (the largest objects in this zone are dwarf planets) and the material is essentially unchanged since the period of planet formation in our solar system.  Measuring the contents of the Kuiper belt  is expected to reveal the distribution of material early in our solar systems formation. Recently we have measured the distribution of number of objects with size for objects with sizes of between 500 to 10 km.  The distribution of these sizes exhibits characteristics that are consistent with the early formation process of planetesimals having been driven by gravitational instabilities in the disk.  Precise determination of shape of the distribution of object sizes will reveal the details of the planetesimal formation. In this proposal we request funds to continue to understand how planets form by exploring the structure of the Kuiper belt.  We will examine the distribution of Kuiper belt object sizes and the orbits of these objects via a set of techniques: - Direct observations using telescopes (in particular the Vera C. Rubin Observatory, James Webb Space Telescope, Hubble Space Telescope, Gemini Observatory, Subaru Telescope and Canada-France-Hawaii Telescope) to find smaller and more distant bodies and measure their physical properties.  We are now developing new 'Machine Learning' techniques to better explore the datasets created by these telescope observations.  - In-situ observations of objects in the Kuiper belt using NASA's New Horizons spacecraft which is currently cruising through the Kuiper belt.  I am a co-Investigator on NASA New Horizons Kuiper Extended Mission and co-Investigator on the proposal to extend mission operations to 2030.  New Horizons provides detailed observations of Kuiper Belt Objects that reveal the structure of their surfaces and these observations can not be made using any other facility than New Horizons. - Detection of very small bodies (about 1km) via stellar occultations. Stellar occultations are dimming of stars when an object passes between the observer and the star.  We measure the existence and size of objects in the Kuiper belt when they cross between us and the distant stars, allowing detection of very small objects. The majority of this research is conducted directly by graduate students as part of their training and in collaboration with prestigious international research teams.