Scientific Goals of FOSSIL

The FOSSIL Survey is an intensive program of the Subaru Telescope using the Hyper Suprime-Cam (HSC) to investigate the formation and evolution of our Solar System. FOSSIL will probe the populations of the Jupiter Trojans (JTs) and Trans-Neptunian Objects in order to learn about their formation histories and dynamical evolution. With the large 8.2 meter aperture of the Subaru telescope and the wide 1.7° field of view of HSC, FOSSIL will be able to probe a wide area of the sky down to a limiting magnitude of r≈26.5. Subaru/HSC is the only instrument in the world capable of mesauring such faint objects over a large region of the sky.

FOSSIL is designed to detect small JTs and distant/small TNOs, to answer specific questions about Solar System formation and evolution which have been left unanswered by earlier observations and will not be well addressed by future surveys. The main scientific goals of the survey are:

High-Inclination and High-Perihelion Objects

What are the population size and orbital distribution of high-i and high-q objects? FOSSIL will use a large and deep survey including off-ecliptic blocks to detect these objects. Their orbital distribution is indicative of the migration of the giant planets and the presence of any undiscovered planets.

Colors of Resonant TNOs

Which surface types are most common in the resonances, and does this vary depending on the resonance location? FOSSIL will specifically target the 3:2, 5:3, 7:4, 2:1, and 5:2 which trapped objects from different formation locations during planetary migration. The color distribution within the resonances constrains the composition of the proto-planetesimal disk.

Plutino Size Distribution

How does the size distribution of Plutinos (3:2) change at small sizes? FOSSIL will robustly measure the number of smaller Plutinos by targeting the regions where they are most detectable. The number of small Plutinos probes their collisional history, formation density, and formation conditions.

Colors and Rotation Periods of Jovian Trojans

Where were the JTs formed and how did they become co-orbitals? FOSSIL will target both the L4 and L5 JT cloud to measure the size distribution, colors, and light-curves of a large sample of JTs. This will constrain the origin and evolution of JTs and the role of Jupiter’s migration in the early Solar System.